Early results of 7.5" Amidion rod
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Hi Roy,
Thanks for the excellent report of your coil winding results with the 7.5"
Amidon rod.
Concerning the modification of the Tecsun PL-300WT/ Grundig G8 models,
Steve Ratzlaff and I did multiple AM "alignments" of the radios by loosening the
stock loopstick coils, and shifting them slightly, while listening for
increasing or decreasing AM signal levels. Most of the PL-300WT/ G8 models
had some AM signal improvement by this procedure, which we used to optimize
reception for various DXers.
After aligning the coils for maximum AM sensitivity, we would always check
the final inductance of the coils after shifting them. In the case of the
PL-300WT/ G8 models, this final coil inductance was always within the 180- 450
uh specification called for in the Si473x spec sheet. Once the optimum coil
inductance was found (most of them were around 300 uh, or fairly close to the
stock coil position), the same coil position provided maximum AM sensitivity
throughout the AM spectrum. Steve and I did about 15 of these alignments, for
ourselves and others. In this regard, the optimum loopstick coil inductances
observed in the PL-300WT/ G8 models never deviated from the 180- 450 uh
specification.
Of course, there were multiple requests for 7.5" Amidon loopstick-modified
PL-300WT/ G8 models at the time, and I made several of these up for myself,
and others. The procedure was to first "align" the stock coil to determine
the optimum inductance value for maximum AM sensitivity (as described above),
then to remove the stock loopstick from the radio, replacing it with an Amidon
7.5" type 61 ferrite bar wound with a fixed 40/44 Litz wire coil of the same
optimal inductance value. The procedure always provided a maximum level of AM
sensitivity from 530- 1700 kHz, with no Si4734 varactor issues on the high band.
About five of these 7.5" loopstick PL-300WT/ G8 models were
constructed here (two going to the Massachusetts DXers Mark Connelly and Chris
Black), and Steve also made several of them-- all of which worked very well in
DXing. The issue was that because the DSP selectivity was fixed at the 3 kHz
setting in these models, these 7.5" loopstick PL-300WT/ G8 models never
were competitive with the CFJ455K5 filter-modified E100 7.5" Slider models in
transoceanic DXing. The fanatical ULR hot-rodders (like me) then decided to hold
off on more modifications, until we could receive some new Si4734 radios
offering the desired 1 kHz DSP selectivity.
I hope this information will be useful.
73 and Good DX,
Gary DeBock
In a message dated 1/13/2010 4:50:53 P.M. Pacific Standard Time,
roy.dyball@... writes:
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Hello Roy and Neil,
Thanks for your comments on our group, Neil.
Roy, in my previous post there was a description of the method that Steve
Ratzlaff and I used to optimize AM reception in the Tecsun PL-300WT and G8
models, and to determine the optimum loopstick coil inductance for peak AM
sensitivity in the stock models (and in the 7.5" Amidon loopstick transplant
models). That procedure is actually described in a file posted in our
Ultralightdx site (under modifications), and is also directly linked at http://www.mediafire.com/?jyjg5hmkyqm .
Once we determined the optimum loopstick coil inductance for peak AM
sensitivity in the models, we simply wound a fixed 40/44 Litz wire coil of
the same inductance on the 7.5" Amidon ferrite bar, and obtained great results
every time. Although their AM sensitivity was equal to the best of the modified
Ultralights, unfortunately the fixed 3 kHz DSP selectivity in the 7.5"
loopstick PL-300WT/ G8 models made them uncompetitive in transoceanic DXing
when compared to the CFJ455K5 filter-modified E100 Slider and SWP Slider 7.5"
loopstick models, so we didn't make too many of the modified PL-300WT/ G8
models last spring.
73 and Good DX, Gary
In a message dated 1/13/2010 5:51:24 P.M. Pacific Standard Time,
neil.findlay52@... writes:
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Roy <roy.dyball@...>
Hi All The first coil was wound on the 7.5 inch rod with 165/46 spaced using 0.7mm solder as the spacer which is about the same size as the Litz, wound over 110mm centred on the rod. The capacitance reported by the G8 showed it had bottomed out at 1710Khz. I removed 2mm from each end and the capacitance showed 18 Pf at 1710Khz (7pf is the lowest). This resulted in aprox 15dbu increase on the G8 when compared to a stock PL-310 set a 3Khz bandwidth, holding this to the end of the band. I was able to hear a station in another state on 1323Mhz (Cruise AM in Adelaide) last night that I have tried on and off and have never been able to receive at a distance of over 1600 KM (great circle) while listening with the radio on my bed side table. I then decided to emulate Gary's 81 turn 40/44 coil starting at 43mm. The G8 reported it was bottoming out of capacitance at 1540Khz. I ran my standard tests and found this configuration was performing the same as the 165/46 coil at the bottom of the band but was dropping off by around 1200Khz (2-3 dbu). I had to unwind 18 turns to get the G8 to report a value of 12pf at 1710Khz. This only dropped the very end of the (low) band by 2 dbu but had started to pick up by 1200Khz. I won't know how well it performs until tonight when the high end of the band opens. For now it is performing aprox 13dbu better than the stock PL-310. Gary has reported that his coil shows a better improvement when fitted to the 380 than the 310. Probably this coil would perform better in the PL-380 than the G8. I will try that later. I am also going to rewind the first coil but use 0.5mm spacing.
Roy.
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neil.findlay52
Hi all
And a question to Roy
Currently using a 310 and a 380 with my Palstar R30a with 3 Kaz antennae as my spotter reciever
Just got my order of 40/44 litz wire, not yet got the Amidon rods. I do have a flat rod of unknown
ferrite type ( probably bought from local electronics supplier years ago ) it is 7&7/8 inch long by
3/4inch by 3/16 inch - The comment seem to indicate that flat is not ideal but at that size would it
be worth a try. I am off work / working from home at around 40% for two weeks after a minor
operation so will have some time and the Amidon rods wont arrive in that time.
Roy
I am interested in what ypu have been able to hear from the East and North East also have you
ever heard a Western Australian station. I live at Rothwell ( on the edge of Deception Bay) just
going off the Redcliffe Peninsular. I have heard Fiji and many New Zealanders. I can hear a lot
of asians but not good at recognising the languages. My son knows some japanese and can rcognise
so will try for some of the powerhouses that Gary hears ie 747 etc. I have never heard a West Aust
yet. My other project is to get the Vactrol connected to the 3 Kaz antenna and wind a coupling on to
the 380 - I have some wire wrap from years ago computer projects.
This is the best group that I have part of in Medium Wave - a most co-operative group covering
listening and technical even part of the design team of our prime chip. Thank you for everyones effort
and for making the information available
Neil
From: Roy To: ultralightdx@... Sent: Thu, 14 January, 2010 10:50:38 AM Subject: [ultralightdx] Early results of 7.5" Amidion rod
Hi All The first coil was wound on the 7.5 inch rod with 165/46 spaced using 0.7mm solder as the spacer which is about the same size as the Litz, wound over 110mm centred on the rod. The capacitance reported by the G8 showed it had bottomed out at 1710Khz. I removed 2mm from each end and the capacitance showed 18 Pf at 1710Khz (7pf is the lowest). This resulted in aprox 15dbu increase on the G8 when compared to a stock PL-310 set a 3Khz bandwidth, holding this to the end of the band. I was able to hear a station in another state on 1323Mhz (Cruise AM in Adelaide) last night that I have tried on and off and have never been able to receive at a distance of over 1600 KM (great circle) while listening with the radio on my bed side table. I then decided to emulate Gary's 81 turn 40/44 coil starting at 43mm. The G8 reported it was bottoming out of capacitance at 1540Khz. I ran my standard tests and found this configuration was performing the same as the 165/46 coil at the bottom of the band but was dropping off by around 1200Khz (2-3 dbu). I had to unwind 18 turns to get the G8 to report a value of 12pf at 1710Khz. This only dropped the very end of the (low) band by 2 dbu but had started to pick up by 1200Khz. I won't know how well it performs until tonight when the high end of the band opens. For now it is performing aprox 13dbu better than the stock PL-310. Gary has reported that his coil shows a better improvement when fitted to the 380 than the 310. Probably this coil would perform better in the PL-380 than the G8. I will try that later. I am also going to rewind the first coil but use 0.5mm spacing.
Roy.
See what's on at the movies in your area. Find out now. |
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Roy <roy.dyball@...>
Thank you Gary and Neil. Having the Si4734 tell you what's going on regarding the capacitance/inductance of the loopstick is a real bonus and makes fine tuning easy. Gary I think the 81 turn coil is too big. The 81 turn coil really worked well on LW, it was almost 45 dbu and 25 S/n db above the stock PL-310 on my local NDB (311Khz). At 81 turns the G8 reported the inductance as 630 uh at 520Khz. Neil I would not hesitate to use your ferrite rod to practice with until your Amidon rod arrives. I would use the wire wrap wire and work on a coil length of 30mm or 60mm for spaced winding (just wind two wires together then unwind one). I also have never heard a station from Western Australia. Receiving 1323 Cruise AM last night is my best so far (1600KM) without an external aerial. I woke up about 3AM and just had to try the 7.5 inch Amidon, admittedly I had turned off the soft mute on the G8 and had selected 2Khz bandwidth. I find 1Khz although showing better S/N can be a bit muffled when you are trying to get an ID. Winding coils is fast and easy with these little Tecsun's so wind a couple of different configurations and compare them. I hope it works out well. Cheers Roy --- In ultralightdx@..., D1028Gary@... wrote:
> > Hello Roy and Neil, > > Thanks for your comments on our group, Neil. > > Roy, in my previous post there was a description of the method that Steve > Ratzlaff and I used to optimize AM reception in the Tecsun PL-300WT and G8 > models, and to determine the optimum loopstick coil inductance for peak AM > sensitivity in the stock models (and in the 7.5" Amidon loopstick transplant > models). That procedure is actually described in a file posted in our > Ultralightdx site (under modifications), and is also directly linked at > _http://www.mediafire.com/?jyjg5hmkyqm_ (http://www.mediafire.com/?jyjg5hmkyqm) . > > Once we determined the optimum loopstick coil inductance for peak AM > sensitivity in the models, we simply wound a fixed 40/44 Litz wire coil of the > same inductance on the 7.5" Amidon ferrite bar, and obtained great results > every time. Although their AM sensitivity was equal to the best of the > modified Ultralights, unfortunately the fixed 3 kHz DSP selectivity in the 7.5" > loopstick PL-300WT/ G8 models made them uncompetitive in transoceanic DXing > when compared to the CFJ455K5 filter-modified E100 Slider and SWP Slider > 7.5" loopstick models, so we didn't make too many of the modified PL-300WT/ > G8 models last spring. > > 73 and Good DX, Gary > > > > > > > In a message dated 1/13/2010 5:51:24 P.M. Pacific Standard Time, > neil.findlay52@... writes: > > > > > > Hi all > And a question to Roy > > Currently using a 310 and a 380 with my Palstar R30a with 3 Kaz antennae > as my spotter reciever > > Just got my order of 40/44 litz wire, not yet got the Amidon rods. I do > have a flat rod of unknown > ferrite type ( probably bought from local electronics supplier years ago ) > it is 7&7/8 inch long by > 3/4inch by 3/16 inch - The comment seem to indicate that flat is not ideal > but at that size would it > be worth a try. I am off work / working from home at around 40% for two > weeks after a minor > operation so will have some time and the Amidon rods wont arrive in that > time. > > Roy > I am interested in what ypu have been able to hear from the East and North > East also have you > ever heard a Western Australian station. I live at Rothwell ( on the edge > of Deception Bay) just > going off the Redcliffe Peninsular. I have heard Fiji and many New > Zealanders. I can hear a lot > of asians but not good at recognising the languages. My son knows some > japanese and can rcognise > so will try for some of the powerhouses that Gary hears ie 747 etc. I have > never heard a West Aust > yet. My other project is to get the Vactrol connected to the 3 Kaz antenna > and wind a coupling on to > the 380 - I have some wire wrap from years ago computer projects. > > This is the best group that I have part of in Medium Wave - a most > co-operative group covering > listening and technical even part of the design team of our prime chip. > Thank you for everyones effort > and for making the information available > > Neil > > > > ____________________________________ > From: Roy roy.dyball@... > To: ultralightdx@ ultrali > Sent: Thu, 14 January, 2010 10:50:38 AM > Subject: [ultralightdx] Early results of 7.5" Amidion rod > > > Hi All > The first coil was wound on the 7.5 inch rod with 165/46 spaced using > 0.7mm solder as the spacer which is about the same size as the Litz, wound over > 110mm centred on the rod. The capacitance reported by the G8 showed it had > bottomed out at 1710Khz. I removed 2mm from each end and the capacitance > showed 18 Pf at 1710Khz (7pf is the lowest). This resulted in aprox 15dbu > increase on the G8 when compared to a stock PL-310 set a 3Khz bandwidth, > holding this to the end of the band. > I was able to hear a station in another state on 1323Mhz (Cruise AM in > Adelaide) last night that I have tried on and off and have never been able to > receive at a distance of over 1600 KM (great circle) while listening with > the radio on my bed side table. > I then decided to emulate Gary's 81 turn 40/44 coil starting at 43mm. The > G8 reported it was bottoming out of capacitance at 1540Khz. I ran my > standard tests and found this configuration was performing the same as the 165/46 > coil at the bottom of the band but was dropping off by around 1200Khz (2-3 > dbu). > I had to unwind 18 turns to get the G8 to report a value of 12pf at > 1710Khz. This only dropped the very end of the (low) band by 2 dbu but had > started to pick up by 1200Khz. I won't know how well it performs until tonight > when the high end of the band opens. For now it is performing aprox 13dbu > better than the stock PL-310. > Gary has reported that his coil shows a better improvement when fitted to > the 380 than the 310. Probably this coil would perform better in the PL-380 > than the G8. I will try that later. I am also going to rewind the first > coil but use 0.5mm spacing. > > Roy. > > > > > > > ____________________________________ > See what's on at the movies in your area. _Find out now_ > (http://au.rd.yahoo.com/movies/mailtagline/*http://au.movies.yahoo.com/session-times/) . > |
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Hi Roy,
Thanks for your comments, and experimental results.
I don't know if you received the previous message, but in the case of the
Tecsun PL-300WT/ Grundig G8 models, Steve and I never wound an 81-turn coil
on the 7.5" Amidon type 61 ferrite bar. We were able to find the optimum
loopstick coil inductance value for each model by removing the wax from the
stock loopstick coil, then sliding the coil along the ferrite bar to peak the AM
sensitivity during live signal reception. We would then record this
inductance value (which was always between 180-450 uh, and usually pretty close
to 300 uh) and then either secure the stock coil in this new position (for stock
model optimum AM sensitivity) or remove the stock loopstick and use this optimum
inductance value in a transplanted 7.5" loopstick (by winding a fixed 40/44 Litz
wire coil of the same inductance on the Amidon type 61 ferrite bar). In either
case, maximum AM sensitivity was then obtained for the size of either
loopstick.
This approach is not possible with the D96L, PL-310 or PL-380 loopsticks,
because the stock coil Litz wire turns are glued on the ferrite bar, and
the coil cannot be shifted on the bar, as in the G8/ PL-300WT models. This is
why an 81-turn Slider coil was constructed for use on the 7.5" Amidon ferrite
bar, to provide the same function of shifting the inductance to peak the AM
sensitivity during live signal reception, then matching this optimum inductance
in a transplanted loopstick.
Since most of the PL-300WT/ G8 models had an optimum matching
inductance fairly close to 300 uh, if you wind a coil of similar
inductance on your 7.5" type 61 bar, you will probably achieve a great increase
in AM sensitivity across the band, relative to the stock G8. If you wish to
fine-tune the optimum inductance to the exact value, you can slide the
stock loopstick coil during live AM signal reception (as described above), then
match the related inductance value in a new 7.5" loopstick coil. This was the
procedure Steve and I used to provide 7.5" loopstick G8 and PL-300WT models for
about 7 different DXers, all of which had excellent AM sensitivity across
the band.
I hope this information will be useful in your experiments, and thanks
again for your participation.
73, Gary
In a message dated 1/14/2010 1:14:13 A.M. Pacific Standard Time,
roy.dyball@... writes:
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jim_kr1s <jkearman@...>
For any ferrite rod used in a DSP-based Tecsun radio, there is an "optimum inductance," but this is not because of the chip. The antenna circuit is a simple parallel-LC combination, as verified by Roy.
A slab of ferrite will have a frequency at which its Q is highest. See the recent measurements by Steve Ratzlaff. If you wind a coil that resonates with the on-chip varactor at that frequency, you will achieve a peak there. This does not guarantee that the coil will resonate across the band, or even inside the band. It seems likely the 554-uH inductors are not resonating up to 1710 kHz. The larger, lower-loss rod used in the Amidon mods is significantly better than the stock rod, and displacing the rod from the circuit board further improves results. This does not axiomatically imply the antenna is working at its best. Roy has several times shown that the chip cannot produce capacitance low enough to resonate that inductance at 1710 kHz, especially when several picofarads of stray capacitance is present, as is the case with the wires leading up to the external rods. Numerous qualified experimenters, such as Dan McGillis and Ben Tongue, have determined that ferrite-rod inductors wound on the center of the rod outperform those wound at the ends. Ferrite 61/Paul S recently posted an extensive analysis of ferrites; well worth reading. It's also been shown that spacing the turns, rather than winding them close together, yields higher Q. Roy recently confirmed this as well. If we accept the reality of how these circuits work, we can make even better radios. There is no mystery here. The idea of replacing the antennas is good. I want to see even better antennas, and I don't care who gets the credit. Here in frozen Florida, I've been measuring core Qs by a method developed by Wes Hayward, W7ZOI. I think the paper was mentioned here recently. Steve Ratzlaff sure nailed that one: The Tecsun antennas are poor performers. I've also been experimenting with air-core loops resonated by the chip. This is the way to go if you're going to use an external loop. No need for a spotter radio or fussing with the tuning cap. The radio will do it for you. With a simple 4:1 bifilar-wound balun-type transformer, you can use a loop with fewer turns, too, which makes for easier construction. The trick is fitting in the balun and a jack that disconnects the internal antenna when you plug in the external loop. Coupling into the internal loop and tuning the external one, defeats one of the main advantages of the chip: Its ability to resonate an antenna of the correct inductance. 73, Jim, KR1S |
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Roy <roy.dyball@...>
Gary The G8 and the Pl-380 have almost identical front end circuit boards. They use the same chip. In both the radios the antenna goes straight to the Si4734 (pin 4) via only a coupling capacitor. The only additional circuitry is the addition of the SW preamp to the AM. At some stage I will disconnect the SW node to see what difference that makes I am using the G8 as a test bed to report back the inductance/capacitance of the loopstick that the Si4734 is seeing. I just swapped the loopstick from the G8 and put it in the Pl-380 and ran my standard test. It performed almost identically as in the G8 + or - 1 dbu. I don't have a USB interface connected to my PL-380 as I am waiting until the Ver 40 firmware comes out with the additional bandwidth and power line rejection filters. I believe the PL-380 would report similar inductance/capacitance to the G8 I would also confirm that spacing the coil definitely produces better results in all my cases sometimes +5 dbu and especially at the top of the band. Cheers Roy. --- In ultralightdx@..., D1028Gary@... wrote:
> > Hi Roy, > > Thanks for your comments, and experimental results. > > I don't know if you received the previous message, but in the case of the > Tecsun PL-300WT/ Grundig G8 models, Steve and I never wound an 81-turn coil > on the 7.5" Amidon type 61 ferrite bar. We were able to find the optimum > loopstick coil inductance value for each model by removing the wax from the > stock loopstick coil, then sliding the coil along the ferrite bar to peak > the AM sensitivity during live signal reception. We would then record this > inductance value (which was always between 180-450 uh, and usually pretty > close to 300 uh) and then either secure the stock coil in this new position > (for stock model optimum AM sensitivity) or remove the stock loopstick and > use this optimum inductance value in a transplanted 7.5" loopstick (by > winding a fixed 40/44 Litz wire coil of the same inductance on the Amidon type 61 > ferrite bar). In either case, maximum AM sensitivity was then obtained for > the size of either loopstick. > > This approach is not possible with the D96L, PL-310 or PL-380 loopsticks, > because the stock coil Litz wire turns are glued on the ferrite bar, and > the coil cannot be shifted on the bar, as in the G8/ PL-300WT models. This is > why an 81-turn Slider coil was constructed for use on the 7.5" Amidon > ferrite bar, to provide the same function of shifting the inductance to peak the > AM sensitivity during live signal reception, then matching this optimum > inductance in a transplanted loopstick. > > Since most of the PL-300WT/ G8 models had an optimum matching inductance > fairly close to 300 uh, if you wind a coil of similar inductance on your > 7.5" type 61 bar, you will probably achieve a great increase in AM sensitivity > across the band, relative to the stock G8. If you wish to fine-tune the > optimum inductance to the exact value, you can slide the stock loopstick coil > during live AM signal reception (as described above), then match the > related inductance value in a new 7.5" loopstick coil. This was the procedure > Steve and I used to provide 7.5" loopstick G8 and PL-300WT models for about 7 > different DXers, all of which had excellent AM sensitivity across the band. > > I hope this information will be useful in your experiments, and thanks > again for your participation. > > 73, Gary > > > In a message dated 1/14/2010 1:14:13 A.M. Pacific Standard Time, > roy.dyball@... writes: > > > > > Thank you Gary and Neil. > Having the Si4734 tell you what's going on regarding the > capacitance/Having the Si4734 tell you what's going on regarding the > capacitance/ > think the 81 turn coil is too big. The 81 turn coil really worked well on LW, > it was almost 45 dbu and 25 S/n db above the stock PL-310 on my local NDB > Neil I would not hesitate to use your ferrite rod to practice with until > your Amidon rod arrives. I would use the wire wrap wire and work on a coil > length of 30mm or 60mm for spaced winding (just wind two wires together then > unwind one). > I also have never heard a station from Western Australia. Receiving 1323 > Cruise AM last night is my best so far (1600KM) without an external aerial. > I woke up about 3AM and just had to try the 7.5 inch Amidon, admittedly I > had turned off the soft mute on the G8 and had selected 2Khz bandwidth. I > find 1Khz although showing better S/N can be a bit muffled when you are > trying to get an ID. > Winding coils is fast and easy with these little Tecsun's so wind a couple > of different configurations and compare them. I hope it works out well. > Cheers Roy > --- In ultralightdx@ In ultra--- In ultralight--- In ultra > > > > Hello Roy and Neil, > > > > Thanks for your comments on our group, Neil. > > > > Roy, in my previous post there was a description of the method that > Steve > > Ratzlaff and I used to optimize AM reception in the Tecsun PL-300WT and > G8 > > models, and to determine the optimum loopstick coil inductance for peak > AM > > sensitivity in the stock models (and in the 7.5" Amidon loopstick > transplant > > models). That procedure is actually described in a file posted in our > > Ultralightdx site (under modifications) Ultralightdx site (under > modificatio > > _http://www. _http://w _http://www. _http://w > _http://www.> > > > Once we determined the optimum loopstick coil inductance for peak AM > > sensitivity in the models, we simply wound a fixed 40/44 Litz wire coil > of the > > same inductance on the 7.5" Amidon ferrite bar, and obtained great > results > > every time. Although their AM sensitivity was equal to the best of the > > modified Ultralights, unfortunately the fixed 3 kHz DSP selectivity in > the 7.5" > > loopstick PL-300WT/ G8 models made them uncompetitive in transoceanic > DXing > > when compared to the CFJ455K5 filter-modified E100 Slider and SWP Slider > > 7.5" loopstick models, so we didn't make too many of the modified > PL-300WT/ > > G8 models last spring. > > > > 73 and Good DX, Gary > > > > > > > > > > > > > > In a message dated 1/13/2010 5:51:24 P.M. Pacific Standard Time, > > neil.findlay52@ neil.findl > > > > > > > > > > > > Hi all > > And a question to Roy > > > > Currently using a 310 and a 380 with my Palstar R30a with 3 Kaz antennae > > as my spotter reciever > > > > Just got my order of 40/44 litz wire, not yet got the Amidon rods. I do > > have a flat rod of unknown > > ferrite type ( probably bought from local electronics supplier years ago > ) > > it is 7&7/8 inch long by > > 3/4inch by 3/16 inch - The comment seem to indicate that flat is not > ideal > > but at that size would it > > be worth a try. I am off work / working from home at around 40% for two > > weeks after a minor > > operation so will have some time and the Amidon rods wont arrive in that > > > time. > > > > Roy > > I am interested in what ypu have been able to hear from the East and > North > > East also have you > > ever heard a Western Australian station. I live at Rothwell ( on the > edge > > of Deception Bay) just > > going off the Redcliffe Peninsular. I have heard Fiji and many New > > Zealanders. I can hear a lot > > of asians but not good at recognising the languages. My son knows some > > japanes e and can rcognise > > so will try for some of the powerhouses that Gary hears ie 747 etc. I > have > > never heard a West Aust > > yet. My other project is to get the Vactrol connected to the 3 Kaz > antenna > > and wind a coupling on to > > the 380 - I have some wire wrap from years ago computer projects. > > > > This is the best group that I have part of in Medium Wave - a most > > co-operative group covering > > listening and technical even part of the design team of our prime chip. > > Thank you for everyones effort > > and for making the information available > > > > Neil > > > > > > > > ____________ ________ ________ _____ > > From: Roy roy.dyball@ F > > To: ultralightdx@ ultrali > > Sent: Thu, 14 January, 2010 10:50:38 AM > > Subject: [ultralightdx] Early results of 7.5" Amidion rod > > > > > > Hi All > > The first coil was wound on the 7.5 inch rod with 165/46 spaced using > > 0.7mm solder as the spacer which is about the same size as the Litz, > wound over > > 110mm centred on the rod. The capacitance reported by the G8 showed it > had > > bottomed out at 1710Khz. I removed 2mm from each end and the capacitance > > > showed 18 Pf at 1710Khz (7pf is the lowest). This resulted in aprox > 15dbu > > increase on the G8 when compared to a stock PL-310 set a 3Khz bandwidth, > > holding this to the end of the band. > > I was able to hear a station in another state on 1323Mhz (Cruise AM in > > Adelaide) last night that I have tried on and off and have never been > able to > > receive at a distance of over 1600 KM (great circle) while listening > with > > the radio on my bed side table. > > I then decided to emulate Gary's 81 turn 40/44 coil starting at 43mm. > The > > G8 reported it was bottoming out of capacitance at 1540Khz. I ran my > > standard tests and found this configuration was performing the same as > the 165/46 > > coil at the bottom of the band but was dropping off by around 1200Khz > (2-3 > > dbu). > > I had to unwind 18 turns to get the G8 to report a value of 12pf at > > 1710Khz. This only dropped the very end of the (low) band by 2 dbu but > had > > started to pick up by 1200Khz. I won't know how well it performs until > tonight > > when the high end of the band opens. For now it is performing aprox > 13dbu > > better than the stock PL-310. > > Gary has reported that his coil shows a better improvement when fitted > to > > the 380 than the 310. Probably this coil would perform better in the > PL-380 > > than the G8. I will try that later. I am also going to rewind the first > > coil but use 0.5mm spacing. > > > > Roy. > > > > > > > > > > > > > > ____________ ____ ____ _ > > See what's on at the movies i n your area. _Find out now_ > > (http://au.rd. (http (http://au. (htt (http:/ (http (http://a (h > > > |
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Hi Roy,
Thanks for your comments, and suggestions, which are appreciated.
Having removed the stock loopsticks from many G8 and PL-380 models, I can
confirm that the coil inductances are quite similar similar, as you describe
(usually fairly close to 300 uh). But having found that Ultralight radios very
rarely have their stock loopstick coils optimized for best AM sensitivity, in
the pre-DSP models, I would always perform AM alignments for myself (and
others), before using the radios for actual DXing.
When the first PL-300WT models were received from China, our ULR group was
intensely interested in the "no alignment needed" design of the Si4734 DSP
chip. After receiving my first PL-300WT model and finding the loopstick coil had
a movable form (movable with difficulty, actually), I decided to verify that
shifting the coil would not result in any improvement in AM sensitivity. In
fact, moving the coil had a major effect on AM sensitivity in the PL-300WT/ G8
models, so that shifting the coil to peak the strength of a live
AM signal almost always resulted in an improvement in AM sensitivity across the
band. This was a different result than was obtained in traditional radio front
ends, however, in which the coil position for peak AM sensitivity would
shift according to changes in the AM frequency.
After this discovery, the "shifting coil" peaking test became standard
procedure for Steve Ratzlaff and me, as we optimized the AM sensitivity in
various PL-300WT and G8 models. Listening for actual changes in the reception
quality of live, weak AM signals (as the loopstick coil was
shifted) always gave us the best results, and using the related inductance
value was the key for winding a 40/44 Litz wire coil, on the type 61 7.5" Amidon
transplanted loopsticks.
Although the PL-310 and PL-380 models do not have the
same movable coil form on their stock loopsticks, the same concept provides
excellent results when an 81-turn Slider coil is used on a 7.5" Amidon type 61
ferrite bar, to search for the inductance which provides maximum AM sensitivity
in these Si4734 models. This live-signal test on weak AM signals is always
a shortcut to success, and can immediately correct for any possible circuitry
changes in either the DSP chip, or the radio model. The Slider coil covers a
range from zero up to 700 uh, and can always provide a sharp
audio reception peak in the Si4734 model whenever the coil is close to
the optimum inductance value. Unfortunately, the construction of a Slider
coil (described in an article at http://www.mediafire.com/?nqggfm2jymc )
can be somewhat tricky without some experience, but having made up many of
these for various E100 and C.Crane SWP models used in DXpeditions, I would be
happy to make one up for any serious experimenter who wishes to
optimize the AM reception in an Si4734 model with a 7.5" transplanted
loopstick. Steve's comment about close-spaced Litz wire (which was also made at
the very beginning of our ULR tinkering effort two years ago) motivated me to
use such close-spaced Litz wire in many experimental loopsticks, including
the 7.5" loopstick PL-380 (which was recently developed). These loopsticks (both
Slider and fixed-coil) have been successfully used both in travel
situations and DXpeditions by many DXers during this period, including recently
by noted TP-DXer Walt Salmaniw, who visited eastern Australia with his
Slider E100 a few months back.
Thanks again for your comments, Roy, and I hope this information will be of
interest to you.
73, Gary
In a message dated 1/14/2010 12:32:25 P.M. Pacific Standard Time,
roy.dyball@... writes:
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sdwillingham
Roy,
toggle quoted message
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Disconnecting the SW amp is a trivial modification. There is a switching diode that connects the SW amp to the AMI node on the rear circuit board. Just clip the lead on this diode and gently bend it aside. That's it! To reconnect, bend the diode back in place and add a drop of solder. On my PL-300, this mod reduces parasitic capacitance from about 8.5 pF to about 5.25 pF. If my measurements (based on varactor readings) and calculations are correct, the stock configuration can resonate up to about 550uH at 1710 MHz (sound familiar? :). With the clipped diode, about 700 uH may resonate. By the way, I am undecided about whether these high inductances are "optimal", but they seem within the range of Si4734 resonance. There will also be unit-to-unit variations due to manufacturing tolerances and PCB versions. -Scott- --- In ultralightdx@..., "Roy" <roy.dyball@...> wrote:
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jim_kr1s <jkearman@...>
--- In ultralightdx@..., "sdwillingham" <sdwillingham@...>
wrote: If my measurements (based on varactorI stand corrected, and apologize to Gary for doubting him. But yesterday, he got a peak response at around 330 uH on an internal loopstick. I'm trying to understand this. His external antenna has to have more stray C, due to the longer leads. So either the proximity of the internal antenna to the circuit board is detuning it, or the Tecsun ferrite has peak Q at a frequency far from -61's. 73, Jim, KR1S http://qrp.kearman.com/ |
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Hi Scott,
Thanks once again for sharing expert information on the Si4734 design,
and also your calculations of the ability of the stock configuration
to resonate up to about 550 uh. As you may have guessed, I'm inclined to agree
with you :-)
The design, installation and function of the Si4734 DSP chips have been of
intense interest to our Ultralight radio group since the first Tecsun PL-300WT
models were received here in late May, and at that time we immediately
commenced weird efforts in an attempt to make the radios more
sensitive on the AM band.
The key to successful 7.5" loopstick transplants (as obtained in previous
traditional radio models) was simply to measure the inductance of the stock
coil(s) after a proper RF alignment, and match that inductance in a
transplanted loopstick coil. So long as quality loopstick materials
were used (such as a type 61 bar and 40/44 Litz wire), perfect AM sensitivity
results were guaranteed every time.
When the first PL-300WT's appeared, however, we were faced with a puzzle.
The Si4734 spec sheet mentioned the "no AM alignment needed" feature, but the
loopstick coils were wound on a form which typically could be slid for
alignment purposes. Although 99% of the PL-300WT purchasers left
the loopstick coil alone, a couple of performance
fanatics (including myself) couldn't resist moving the coil, to see if the
radio could be aligned on AM like a traditional radio. After an eternity of
scraping wax and probing the reluctant coil form, I did manage to get it moving
(presumably only a second before it self-destructed). So did the radio align
like a traditional radio? Well, yes and no. Like a traditional radio, it did
have a noticeable peak in AM weak signal reception when I slid the coil a few mm
to the right of the original position (moving the inductance up from 290 to 320
uh, as I recall), but unlike a traditional radio, this new coil
position provided maximum reception of AM weak-signal stations through the
entire 530-1700 kHz AM range. As such, the technical fanatics among our
group (Steve Ratzlaff, John Bryant, myself and others) became
convinced that the key to optimizing AM reception in the Si4734 models was to
find this optimal inductance value, and either secure the stock loopstick coil
at this point (for alignment purposes), or match this inductance in a new
transplanted loopstick coil.
The appearance of the Si4734 models without this traditional loopstick coil
form (D96L, PL-310, PL-380) meant that we could no longer use a sliding
loopstick coil form, to find this optimal inductance value during live reception
of weak AM stations. So I decided to turn to an innovative loopstick coil
we had previously developed here in our ULR group to maximize reception in the
Eton E100 models-- the inductance-shifting Slider loopstick. This coil
could quickly change inductance from zero up to 700 uh, and when
transplanted directly into an Si4734 model's loopstick circuitry, could
immediately give us an accurate inductance reading of the coil position which
provided maximum AM weak signal sensitivity in any Si4734 model (similar to the
function of the sliding coil forms, in the stock PL-300WT/ G8 models).
This was the theory behind the optimal inductance test I ran on the Tecsun
PL-380 model using the 81-turn Slider coil, which provided the 550 uh
inductance reading essential for the 7.5" loopstick transplants. The beauty
of this approach is that it always corrects for any changes in either the Si4734
chip or radio circuitry, to provide an inductance which has actually been proven
to provide the best possible reception of weak signals on the AM band. As
such, anyone using such a system (with quality transplant materials) can have
assurance that his new loopstick is providing the best possible AM reception for
its size.
Thanks for listening, Scott, and thanks also for your participation in
the design team which has provided us with such a fascinating component--
completely transforming pocket radios into transoceanic DXing wonders.
73 and Good DX,
Gary DeBock, N7EKX (FCC-tested Extra Class
:-)
In a message dated 1/15/2010 7:30:44 A.M. Pacific Standard Time,
sdwillingham@... writes:
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sdwillingham
Yeah, I'm still trying to understand all the factors that play in the loopstick game. I think in addition to Q limits, there are several parasitics that can confound the numbers. If one is trying to push the inductor to its upper limits, and consequently the capacitance to mimimal levels, the parasitics become even more critical.
toggle quoted message
Show quoted text
I will slightly amend what I said about the stock inductance range topping out at about 550 uH. My assumption there is that parasitic capacitance stays constant. It occurs to me now that as the inductance is increased, the loopstick's self-capacitance will increase as well, limiting the ultimate achievable inductance. On the other hand, at 10% too high inductance, you will only give up at the top 5% of the band. And if the Q at the top of the band is only 20... I'm glad Gary has the energy to do all those experiments! -Scott- --- In ultralightdx@..., "jim_kr1s" <jkearman@...> wrote:
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Roy <roy.dyball@...>
Hi Scott Thank you for the tip with the diode I will try this with a larger coil as I believe this provides greater signal due to increased transformer action. I also believe in the standard configuration the chip will perform with an inductance up to 550uh.To me it makes absolute sense to use the figures that the Si4734 is returning regarding capacitance/inductance when building loopstick coils. It seems to me that the chip's returned values are what it is actually seeing and are the appropriate values to use. All I can do is accurately pass on my findings from the experiments I conduct and as is often the case they will differ from others. My recent findings with winding an 81 turn coil of 40/44 Litz wire on an Amidon 61 7.5" rod showed different results to Gary's. Maybe as more people wind coils we will find out why our results differ and this is the real fun of group experimentation. I am looking forward to continuing to wind more coils and have some 630 strand Litz (rope) for my next coil on the 7.5" rod. So far the best results obtained have been from the 165/36 spaced coil on the 7.5" rod. I also believed that there was no need to space Litz wire but my empirical results have shown an approximate 2dbu increase in all the coils I have wound as close spaced and have unwound and using the same wire rewound as single wire spaced. These are all the mysteries of loopstick tinkering. Cheers Roy. --- In ultralightdx@..., "sdwillingham" wrote: > > > Yeah, I'm still trying to understand all the factors that play in the loopstick game. I think in addition to Q limits, there are several parasitics that can confound the numbers. If one is trying to push the inductor to its upper limits, and consequently the capacitance to mimimal levels, the parasitics become even more critical. > > I will slightly amend what I said about the stock inductance range topping out at about 550 uH. My assumption there is that parasitic capacitance stays constant. It occurs to me now that as the inductance is increased, the loopstick's self-capacitance will increase as well, limiting the ultimate achievable inductance. On the other hand, at 10% too high inductance, you will only give up at the top 5% of the band. And if the Q at the top of the band is only 20... > > I'm glad Gary has the energy to do all those experiments! > > -Scott- > > --- In ultralightdx@..., "jim_kr1s" jkearman@ wrote: > > > > > > > > --- In ultralightdx@..., "sdwillingham" > > wrote: > > > If my measurements (based on varactor > > > readings) and calculations are correct, the stock configuration > > > can resonate up to about 550uH at 1710 MHz (sound familiar? :). > > > With the clipped diode, about 700 uH may resonate. > > > > I stand corrected, and apologize to Gary for doubting him. But > > yesterday, he got a peak response at around 330 uH on an internal > > loopstick. I'm trying to understand this. His external antenna has to > > have more stray C, due to the longer leads. So either the proximity of > > the internal antenna to the circuit board is detuning it, or the Tecsun > > ferrite has peak Q at a frequency far from -61's. > > > > 73, > > > > Jim, KR1S > > http://qrp.kearman.com/ > > > |
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Hi Roy,
Thanks for your experimental observations, which are appreciated. We are
all striving to create the most effective loopsticks for the Si4734 radio
models, and actual experimentation (and comparison of results) is certainly
the key to success.
Regarding the 81-turn coil of 40/44 Litz wire on the 7.5" Amidon
ferrite bar (providing an approximate 554 uh inductance, as measured on the BK
Precision 875B LCR meter), this inductance value was obtained on the PL-380
model, at the (variable-inductance) Slider coil position actually providing
the best reception of a weak AM signal, using detailed averaging of the RSSI and
S/N readings after a clear audio reception peak was found by sliding the coil.
The Slider coil and 7.5" Amidon type 61 ferrite bar had been transplanted
into the PL-380 circuitry for these tests, replacing the stock ferrite bar
(which had fixed Litz wire turns, making such a test impossible).
This experiment was not run on the PL-300WT/ G8 models, because the stock
loopstick coil could be shifted to provide the same optimal inductance test
under live AM weak-signal reception conditions (although the coil form was
occasionally very reluctant to get moving, as we found out with dismay
in the early PL-300WT models :-) According to the investigations made by Steve
Ratzlaff and me on about 15 different radios, these optimal inductances for the
PL-300WT and G8 models always were within the 180- 450 uh specification called
for in the Si4734 spec sheet, and never anywhere close to 554 uh. As such,
attempting to duplicate the PL-380 experimental results (and the
related 554 uh inductance value) with the PL-300WT (or its G8 clone) model
will never be successful, and we are on agreement with this
point. Actual live-signal experimental results obtained by Steve and I
on the PL-300WT/ G8 models indicated that most of these models
provided the best reception of AM signals at loopstick coil inductances
around 300 uh (although there were a couple of oddballs that optimized
around 210 uh, and one at 410
uh).
The supreme advantage of using variable-inductance Slider coil tests
to determine optimal loopstick coil inductance in the Si4734 models is that
the system immediately corrects for any changes in the Si4734 chips or
different radio model circuitry, so that the coil inductance is
actually proven to provide optimal reception of weak AM stations during live
reception conditions in a certain model. The sliding-coil experimentation
in the PL-380 model determined a different optimal AM inductance value (554 uh)
than the tests run on the PL-300WT/ G8 models (always between 180-450
uh, but usually around 300 uh). In this case, there has apparently been a
change made either in the Si4734 chips and/ or the Tecsun circuitry in the two
different models, but in either case optimal AM reception was obtained at
the inductance values determined by the sliding-coil tests. Since optimal AM
weak-signal reception is the standard of success for 99% of our ULR
group, from my own perspective I will be content to use loopsticks proven
to provide this optimal AM inductance value, without worrying too much about
which changes were made in the chips (or radios) to require differing
optimal inductance values in the G8 and PL-380 models.
73 and Good DX,
Gary
In a message dated 1/16/2010 4:57:51 A.M. Pacific Standard Time,
roy.dyball@... writes:
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Hi Scott,
Thanks again for your observations, and I certainly concur that the
loopstick experimentation with the Si4734 models is fascinating. Your expert
comments are certainly appreciated, as well as Roy's detailed
experimentation.
Regarding the D96L optimal inductance tests for maximum AM sensitivity in
the model, of course I'm fully aware of John's experimental results. During this
summer experimentation, we ran tests independently with differing test
equipment, and obtained differing results. John and I have essentially agreed to
disagree about the D96L results,and I refrained from publishing my own results
(which indicated the familiar 554 uh optimal inductance value) until John and I
could get together and sort out our differences during mutual
experimentation. We continue to respect each other's technical abilities and
have maintained a close friendship, and accept each other's contributions as
part of the process toward total experimental success. I certainly appreciate
Roy contributions, as well as those of Steve and other experimenters, and hope
that we can all make progress toward our mutual goal of extremely effective
loopsticks.
Nobody has a monopoly on loopstick knowledge or creativity, and as long as
we have an open policy of open contribution and respect for differing opinions,
we certainly can make further design breakthroughs in
creating DX-oriented antennas.
73 and Good DX, Gary
In a message dated 1/16/2010 11:12:18 A.M. Pacific Standard Time,
sdwillingham@... writes:
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sdwillingham
Gary,
toggle quoted message
Show quoted text
Thanks for sharing your many experimental results with us. The results that you and others in the group have reported are fascinating. I have some experiments of my own to share, but haven't put them together yet. The peaking alignment results for the PL-300 WT "World Time Travel Radio" :) are puzzling to me, but I do take them seriously. I am experimenting with the same model and have questions about my own data too. An interesting contrast is John Bryant's results on the Kchibo D96L over at dxer.ca: http://www.dxer.ca/file-area/doc_download/253-alignment-of-the-kchibo-d96l-ultralight Clearly there is more to learn about core materials, parasitics, and metal proximity effects. The other night, I was curious how well my measurements and calculations predicted the loopstick inductance, so I desoldered the loopstick in my PL-300 and attached a brand-new Toko metal-can inductor, rated 330 uH with Q > 80 at 796 kHz. I first measured the inductor on an Extech LCR meter, which indicated 324 uH at 1 kHz. In the PL-300, I measured the varactor values at 520 and 1710 kHz. Calculation from those values gives me an inductance of 322 uH. Not bad agreement. But in-circuit Q values seem nowhere near 80. So my Q estimation methods leave something to be desired. (Note that the Extech meter indicates around 330 uH at 1 kHz for my loopstick which is slightly modified. The Si4734 varactor "sees" 280 uH in the MW band. Thus I'm a bit skeptical of whether LCR measurements at low frequencies translate well for certain ferrite materials.) -Scott- --- In ultralightdx@..., D1028Gary@... wrote:
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Pollock,Raphael E <rpollock@...>
Hi Gary! From: ultralightdx@... <ultralightdx@...> To: ultralightdx@... <ultralightdx@...> Sent: Sat Jan 16 14:35:49 2010 Subject: Re: [ultralightdx] Re: Early results of 7.5" Amidion rod
Hi Roy,
Thanks for your experimental observations, which are appreciated. We are
all striving to create the most effective loopsticks for the Si4734 radio
models, and actual experimentation (and comparison of results) is certainly
the key to success.
Regarding the 81-turn coil of 40/44 Litz wire on the 7.5" Amidon
ferrite bar (providing an approximate 554 uh inductance, as measured on the BK
Precision 875B LCR meter), this inductance value was obtained on the PL-380
model, at the (variable-inductanc
This experiment was not run on the PL-300WT/ G8 models, because the stock
loopstick coil could be shifted to provide the same optimal inductance test
under live AM weak-signal reception conditions (although the coil form was
occasionally very reluctant to get moving, as we found out with dismay
in the early PL-300WT models :-) According to the investigations made by Steve
Ratzlaff and me on about 15 different radios, these optimal inductances for the
PL-300WT and G8 models always were within the 180- 450 uh specification called
for in the Si4734 spec sheet, and never anywhere close to 554 uh. As such,
attempting to duplicate the PL-380 experimental results (and the
related 554 uh inductance value) with the PL-300WT (or its G8 clone) model
will never be successful, and we are on agreement with this
point. Actual live-signal experimental results obtained by Steve and I
on the PL-300WT/ G8 models indicated that most of these models
provided the best reception of AM signals at loopstick coil inductances
around 300 uh (although there were a couple of oddballs that optimized
around 210 uh, and one at 410
uh).
The supreme advantage of using variable-inductance Slider coil tests
to determine optimal loopstick coil inductance in the Si4734 models is that
the system immediately corrects for any changes in the Si4734 chips or
different radio model circuitry, so that the coil inductance is
actually proven to provide optimal reception of weak AM stations during live
reception conditions in a certain model. The sliding-coil experimentation
in the PL-380 model determined a different optimal AM inductance value (554 uh)
than the tests run on the PL-300WT/ G8 models (always between 180-450
uh, but usually around 300 uh). In this case, there has apparently been a
change made either in the Si4734 chips and/ or the Tecsun circuitry in the two
different models, but in either case optimal AM reception was obtained at
the inductance values determined by the sliding-coil tests. Since optimal AM
weak-signal reception is the standard of success for 99% of our ULR
group, from my own perspective I will be content to use loopsticks proven
to provide this optimal AM inductance value, without worrying too much about
which changes were made in the chips (or radios) to require differing
optimal inductance values in the G8 and PL-380 models.
73 and Good DX,
Gary
In a message dated 1/16/2010 4:57:51 A.M. Pacific Standard Time,
roy.dyball@yahoo.
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Roy <roy.dyball@...>
Hi Scott Thank you for all your input, we are all privileged to have your knowledge and experience in this group. Are you able to share how your calculations work for calculating inductance from starting and ending frequencies (520-1710 KHz) from the values returned from the varactor. I am already converting the capacitance returned to inductance at the frequency tuned but of course the value of inductance calculated is different at the top and bottom of the band. I am able to work with these values but it would be good to know the true averaged value. Now that I am almost done with initial loopstick readings I want to move on to winding some toroids to match an incoming long wire antenna. This will replace the loopstick as I am finding the noise generated by the computer when using the USB interface on AM is unacceptable. Have you found that the earth provided from the USB connection from the computer is reducing reception on both AM and FM and is also a source of noise? Cheers Roy.
--- In ultralightdx@..., "sdwillingham" wrote:
> > > > Gary, > > Thanks for sharing your many experimental results with us. The results that you and others in the group have reported are fascinating. I have some experiments of my own to share, but haven't put them together yet. > > The peaking alignment results for the PL-300 WT "World Time Travel Radio" :) are puzzling to me, but I do take them seriously. I am experimenting with the same model and have questions about my own data too. An interesting contrast is John Bryant's results on the Kchibo D96L over at dxer.ca: > > http://www.dxer.ca/file-area/doc_download/253-alignment-of-the-kchibo-d96l-ultralight > > Clearly there is more to learn about core materials, parasitics, and metal proximity effects. > > The other night, I was curious how well my measurements and calculations predicted the loopstick inductance, so I desoldered the loopstick in my PL-300 and attached a brand-new Toko metal-can inductor, rated 330 uH with Q > 80 at 796 kHz. I first measured the inductor on an Extech LCR meter, which indicated 324 uH at 1 kHz. In the PL-300, I measured the varactor values at 520 and 1710 kHz. Calculation from those values gives me an inductance of 322 uH. Not bad agreement. But in-circuit Q values seem nowhere near 80. So my Q estimation methods leave something to be desired. > > (Note that the Extech meter indicates around 330 uH at 1 kHz for my loopstick which is slightly modified. The Si4734 varactor "sees" 280 uH in the MW band. Thus I'm a bit skeptical of whether LCR measurements at low frequencies translate well for certain ferrite materials.) > > -Scott- > > --- In ultralightdx@..., D1028Gary@ wrote: > > > > Hi Scott, > > > > Thanks once again for sharing expert information on the Si4734 design, and > > also your calculations of the ability of the stock configuration to > > resonate up to about 550 uh. As you may have guessed, I'm inclined to agree with > > you :-) > > > > The design, installation and function of the Si4734 DSP chips have been of > > intense interest to our Ultralight radio group since the first Tecsun > > PL-300WT models were received here in late May, and at that time we immediately > > commenced weird efforts in an attempt to make the radios more sensitive on > > the AM band. > > > > The key to successful 7.5" loopstick transplants (as obtained in previous > > traditional radio models) was simply to measure the inductance of the stock > > coil(s) after a proper RF alignment, and match that inductance in a > > transplanted loopstick coil. So long as quality loopstick materials were used > > (such as a type 61 bar and 40/44 Litz wire), perfect AM sensitivity results > > were guaranteed every time. > > > > When the first PL-300WT's appeared, however, we were faced with a puzzle. > > The Si4734 spec sheet mentioned the "no AM alignment needed" feature, but > > the loopstick coils were wound on a form which typically could be slid for > > alignment purposes. Although 99% of the PL-300WT purchasers left the > > loopstick coil alone, a couple of performance fanatics (including myself) couldn't > > resist moving the coil, to see if the radio could be aligned on AM like a > > traditional radio. After an eternity of scraping wax and probing the > > reluctant coil form, I did manage to get it moving (presumably only a second > > before it self-destructed). So did the radio align like a traditional radio? > > Well, yes and no. Like a traditional radio, it did have a noticeable peak in > > AM weak signal reception when I slid the coil a few mm to the right of the > > original position (moving the inductance up from 290 to 320 uh, as I > > recall), but unlike a traditional radio, this new coil position provided maximum > > reception of AM weak-signal stations through the entire 530-1700 kHz AM > > range. As such, the technical fanatics among our group (Steve Ratzlaff, John > > Bryant, myself and others) became convinced that the key to optimizing AM > > reception in the Si4734 models was to find this optimal inductance value, and > > either secure the stock loopstick coil at this point (for alignment > > purposes), or match this inductance in a new transplanted loopstick coil. > > > > The appearance of the Si4734 models without this traditional loopstick coil > > form (D96L, PL-310, PL-380) meant that we could no longer use a sliding > > loopstick coil form, to find this optimal inductance value during live > > reception of weak AM stations. So I decided to turn to an innovative loopstick > > coil we had previously developed here in our ULR group to maximize reception > > in the Eton E100 models-- the inductance-shifting Slider loopstick. This > > coil could quickly change inductance from zero up to 700 uh, and when > > transplanted directly into an Si4734 model's loopstick circuitry, could > > immediately give us an accurate inductance reading of the coil position which > > provided maximum AM weak signal sensitivity in any Si4734 model (similar to the > > function of the sliding coil forms, in the stock PL-300WT/ G8 models). > > > > This was the theory behind the optimal inductance test I ran on the Tecsun > > PL-380 model using the 81-turn Slider coil, which provided the 550 uh > > inductance reading essential for the 7.5" loopstick transplants. The beauty of > > this approach is that it always corrects for any changes in either the > > Si4734 chip or radio circuitry, to provide an inductance which has actually been > > proven to provide the best possible reception of weak signals on the AM > > band. As such, anyone using such a system (with quality transplant materials) > > can have assurance that his new loopstick is providing the best possible > > AM reception for its size. > > > > Thanks for listening, Scott, and thanks also for your participation in the > > design team which has provided us with such a fascinating component-- > > completely transforming pocket radios into transoceanic DXing wonders. > > > > 73 and Good DX, > > Gary DeBock, N7EKX (FCC-tested Extra Class :-) > |
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sdwillingham
Roy,
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The calculation I use is pretty straightforward. The idea is that I assume inductance L is constant across the band and measure the resonating capacitance at two frequencies. I end up with two equations with two unknowns (L and parasitic C) to solve for. So, define: - two frequencies f1 and f2 - corresponding Si4734 varactor readings V1 and V2 - varactor gain G = change in capacitance per varactor code (0.095 pF) First calculate two LC products: - LC1 = 1 / (2*pi*f1)^2 - LC2 = 1 / (2*pi*f2)^2 Assuming constant inductance: LC1 - LC2 = L*(C1 - C2) = L * G*(V1 - V2) Therefore L = (LC1 - LC2) / (G*(V1 - V2)) The capacitances C1 and C2 can then be calculated: C1 = LC1 / L C2 = LC2 / L Each capacitance consists of a fixed and a variable amount: C1 = Cf + G*V1 C2 = Cf + G*V2 So Cf can be calculated as Cf = C1 - G*V1 = C2 - G*V2 Part of Cf can be considered the 7pF documented minimum Si4734 AM input capacitance. The rest is contributed externally, partially by the circuit boards and wires, partially by the loopstick. In my experiments, the stock configuration has about 8.6 pF external capacitance. Lifting the loopstick leads far from the PCB reduces this to 8.0 pF. Clipping the SW diode reduces this to about 5.25 pF with the loopstick leads routed as stock. Regarding noise from the computer connection. This is a difficult problem for AM reception and a slight problem in FM. I've found the noise unacceptable with a desktop compter, but quite a bit less using a laptop with charger _unplugged_. The LCD screen is a problem too. I've been looking at ways to reduce the noise, but there's not a lot to be done at MW frequencies short of an opto-isolated interface. A further problem is that the ground connection to the computer distorts the antenna response (common-mode currents). -Scott- --- In ultralightdx@..., "Roy" <roy.dyball@...> wrote:
Hi Scott |
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