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Re: Graham Maynard's Tecsun PL-380 Modification Article
Hi Roy,
Thanks for your comments, and suggestions throughout the experimentation
(which have all been appreciated).
According to the test results, the choice of coil configuration among
the four test models is not likely to make a significant AM-DXing
difference over the vast majority of MW frequencies. Even on the extreme band
edges, a difference of 1 dB in S/N ratio is unlikely to provide much of a
DXing boost, since live signals typically vary in strength more than this every
few seconds. As you point out, the 300 uh center-wound model would be the most
economic option, and if my location was in Europe, Australia or NZ (with
X-band frequencies as my primary DXing target), the 300 uh coil would be my own
first choice. It's also very suitable for North American DXers who don't care
about LW-DX.
The choice of the 500 uh coil option for myself (and the DXers who have
ordered the modified model) was based on the unsurpassed
performance throughout the MW frequency spectrum during the tests,
plus the fact that it offered LW performance slightly greater than the
lower-inductance models. There was extensive testing on the 1700 kHz frequency
with these 500 uh models, to ensure that there was no trace of varactor
lock-up. Their live-signal reception on 1700 kHz is indeed
equivalent to that of the 300 uh and 400 uh models, and because of
this, the extra LW performance was judged a bonus. The 554 uh model had
varactor lock-up on the out-of-band frequency of 1706 kHz, and although
this did not seem to make much of a difference in its X-band performance, I
lowered the inductance to 500 uh on the "export models," to provide an extra
safety margin. I would recommend that coil options other than the 554
uh model be used for those DXers whose top priority is X-band DXing,
although such a configuration would probably be fine for TP-DXers who rarely
tune those frequencies.
73, Gary
coil configuration would probably be the one I would choose as a DXer in
Australia, NZ or Europe looking for maxim
In a message dated 4/19/2010 7:07:01 P.M. Pacific Daylight Time,
roy.dyball@... writes:
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Re: Graham Maynard's Tecsun PL-380 Modification Article
Roy <roy.dyball@...>
Hi Jim, Just read your description on how you test that the loopstick is resonating and performing correctly into the high end of the band. I agree that this would work well and should be applied as a final check, allowing confidence that the Si4734 is working to its maximum design criteria. I like you have never had good results with high inductance coils (for me above 350uH) finding that by winding them any larger all you are doing is increasing the capacitance which is now working against you to stop the coil resonating at the top of the band. I find the bigger coils (above 400uH) give you a bloated RSSI figures with no improvement in S/N across the MW band. The listening experience is not as good and harsher on the ears. Yes use the bigger coil if you are interested in the low end of the MW band and want better LW performance. The Pl-380 is a great little radio and is designed for capitol city sales (bigger market) where AM signals are at a reasonable level. The Tecsun engineers are not as silly as you think and they know what they are doing. The ferrite rod in the PL-380 is very thin and has in its standard winding configuration about 10pf more capacitance than other larger loopsticks, adding additional turns to this loopstick will increase the capacitance , a fully wound PL-380 ferrite rod would have a very high capacitance and that's why the Tecsun have chosen the values that we have. When you have a properly matched loopstick combination in these little radios the listening experience is obvious and a joy to the ears, but a bigger (inductance) coil is not always better. I feel compelled to publish my results as I believe them to be correct and I know that not everybody will agree. Just as I expect and welcome criticism of my results because it matters not if I am wrong. Similarly I reserve the right to question other people's results not in any other way but with respect. Cheers Roy. --- In ultralightdx@..., "jim_kr1s" wrote:
> > > --- In ultralightdx@..., "sdwillingham" sdwillingham@ > wrote: > > > Summarizing, I agree that loopsticks pushing 500 uH will be fine in MW > and give some extension to LW performance. > > Scott, > > I'll summarize my measurement method because I know you'll understand > it. I'll be glad to email a detailed explanation to anyone who asks. > > Couple a stable signal generator and a measuring device -- which can be > another ULR, an rf voltmeter (I used a selective rf voltmeter also > loosely coupled). or a scope -- into the antenna > > Tune receiver under test and signal generator to, say, 1500 kHz. Observe > voltage. > > Leaving signal generator tuned to 1500 kHz, tune receiver under test > higher in frequency. The voltage should drop as the LC circuit is tuned > out of resonance at 1500 kHz. > > If the voltage does not drop within a few kHz, it implies that the > tuning capacitance has reached its minimum and the radio cannot tune > that inductor to a higher frequency. > > My tests with a 550-uH coil showed it could not be resonated in the > upper part of the MW band. RSSI readings across the band were higher > than with the stock antenna. This is deceiving, and I attribute it to > higher reactance. But the peaking effect of resonance was absent. I note > that coupling the antenna to a large, separately tuned loop antenna will > provide the higher frequency selectivity lost by using the larger > antenna coil. Any 240-uH coil I've tried peaks well anywhere from > 530-1710 kHz, and that's the value I've been using for MW. > > As you mentioned to Stephen, a larger coil delivering more signal to the > receiver on the low end of the band, where it resonates, can create a > new set of problems in areas where there are more strong local stations > than are found in the Seattle area, such as in San Diego, and Stuart, > Florida. > > 73, > > Jim, KR1S > http://kr1s.kearman.com/ > http://qrp.kearman.com/ > |
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Re: Opinions of IDEAL inductance for MW and for LW PL-360?
jim_kr1s <jkearman@...>
--- In ultralightdx@..., "farmerik" wrote: > > > I ran the numbers for a 40 X 40 inch square loop, with 1/3 inch spacing, and came up with 24 turns for 2208 uH. That should do. It looks like my 4 foot loop is around 3500 uH. - FARMERIK That's not bad, only a bit less than a half pound of #28 wire, at 320 feet, about $18.00. The Hoop Loop has 19 feet of wire, and the transformer has less than 30 feet. The toroid cost $7.00 and the Hoop Loop cost $10.00. So I guess you're getting a bargain. Let us know how it works. 73, Jim, KR1S http://kr1s.kearman.com/ http://qrp.kearman.com/ |
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Re: Opinions of IDEAL inductance for MW and for LW PL-360?
Rik
With 7 turns, that loop would be perfect for AM.- FARMERIK
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--- In ultralightdx@..., "farmerik" <farmerik@...> wrote:
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Re: Opinions of IDEAL inductance for MW and for LW PL-360?
Rik
I ran the numbers for a 40 X 40 inch square loop, with 1/3 inch spacing, and came up with 24 turns for 2208 uH. That should do. It looks like my 4 foot loop is around 3500 uH. - FARMERIK
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--- In ultralightdx@..., "jim_kr1s" <jkearman@...> wrote:
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Re: Opinions of IDEAL inductance for MW and for LW PL-360?
jim_kr1s <jkearman@...>
--- In ultralightdx@..., "farmerik" wrote: > > If I wanted to wind an inductive loop antenna to be connected directly to the PL-360, [no lead wire, no cap] what should the values be for MW and for LW ? - FARMERIK You never struck me as the agent provocateur type. :) By now you've seen everyone's comments on MW antennas. For LW, you can calculate based on the predicted maximum C of the radio's tuning cap. The SiLabs data sheet says the chip will tune inductances as low as 180 uH on MW. Assuming it will tune a 180-uH inductance down to 530 kHz, its maximum capacitance is 500 pF. The inductance that resonates with 500 pF at 153 kHz is 2164 uH. Give yourself a little leeway and figure 2200 uH. That inductance will more than cover the full LW band and beyond. WHYN in Springfield will make your radio glow in the dark. For a -61 ferrite rod you'll need about 175 turns, about 23 feet of wire. Using #24 or #28 wire, it will fit nicely on a 7.5-inch rod. Don't even think about making an air-core loop that big, unless you own stock in a copper mine. You won't be hanging that one from your ceiling, either! If you want an air-core loop you'll have to use a transformer. (The usual practice for tuned air-core LW loops is to use combinations of very large fixed and variable capacitors that will resonate with a smaller, practical loop inductance.) The transformers I've used on LW varied from 2650 to 3500 uH. As we know, higher reactance yields greater signal strengths. These inductances work well on the LWBC band, which is 153-279 kHz, and that's where my interest lies. There is far less adjacent-channel interference on LWBC, and the Hoop Loop is small for that band, so I figured a bit more gain wouldn't hurt, as it might on MW. A 3500-uH inductor just covers the entire LW band, including beacons, and that's what I'm currently using. RSSI indications on European and North African LWBC stations run 20-45 dBu, but remember, I'm only 6-10 miles from the ocean. 73, Jim, KR1s http://kr1s.kearman.com/ http://qrp.kearman.com/ |
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Re: Graham Maynard's Tecsun PL-380 Modification Article
Hello All,
Scott is referring to comprehensive measurements performed here on four
different 7.5" loopstick PL-380 test models of varying inductances and coil
configurations, using both signal generator and live signal inputs. These
results have been shared already with those who have made significant
contributions to the 7.5" loopstick experimentation (Roy, Scott, Guy, and
Nick), as well as with the recipients of 7.5" loopstick PL-380 models
prepared here.
Scott's summary is essentially correct, although it was the 554 uh model
that had an indication of varactor lock-up on the (out-of-band) frequency of
1706 kHz. The 500 uh model had unsurpassed RSSI and
S/N performance throughout the MW frequency spectrum, and based
upon this fact and its performance edge on the LW frequencies, it was
chosen as the final configuration for the 7.5" loopstick PL-380 models
shipped to others. The test readings are pasted below, contained in
the pending revision to the PL-380 7.5" loopstick transplant article:
________________________________________________________________________________________
High Sensitivity Coil Options At the suggestion of Scott Willingham (one of the Si4734 design team engineers), various 7.5” loopstick coil inductance models were constructed and tested by the author, to determine the relative coil performance at differing inductances and MW frequencies. In addition, two of the coils were wound in the center of the ferrite bar, to determine if this coil orientation would provide any advantage in the final RSSI and/or S/N readings on the PL-380’s digital display.
Model Model A- 300 uh (center-wound): 54 turns of 40/44 Litz wire, starting 80 mm from either end of the bar Model Model B- 400 uh (center-wound): 64 turns of 40/44 Litz wire, starting 78 mm from either end of the bar Model Model C- 500 uh (offset coil): 75 turns of 40/44 Litz wire, starting 41 mm from closest end of the bar Model Model D- 554 uh (offset coil): 81 turns of 40/44 Litz wire, starting 42 mm from closest end of the bar
These
four test models were extensively compared using both signal generator and live
AM signal inputs, in an outdoor environment free from other conducting
materials. All the loopsticks had identical plastic mounting frames, with rubber
shock mounts isolating the ferrite bars from the plastic. The TSG-17 signal
generator test readings were repeated several times, to ensure stability and
accurate results. The stock PL-380 model was also included in several tests as a
reference, as well as a PL-380 with the stock ferrite bar rewound with 40/44
Litz wire at a 432 uh inductance
(referred to as “Stealth”). The test data (RSSI and S/N) is recorded
below:
Sig. Gen.Test Freq. Stock Stealth 300 uh Model 400 uh Model 500 uh Model 554 uh Model
525 kHz 15/ 00 17/ 00 24/ 07 24/ 07 26/ 08 27/ 08 735 kHz 39/ 13 41/ 14 42/14 43/ 14 1610 kHz 37/ 19 37/ 19 38/ 19 42/ 19 1706 kHz (out of band) 35/ 13 36/ 13 36/ 13 41/ 00
Live Station Signals (averaged readings)
620-KPOJ 19/ 11 20/ 15 33/ 20 34/ 20 34/ 20 35/ 20 750-KXL 30/ 00 32/ 00 39/ 13 41/ 13 43/ 13 43/ 15 1110-KWDB 24/ 09 29/ 11 35/ 20 36/ 20 37/ 20 39/ 20 1600-KVRI 24/ 14 25/ 15 32/ 24 34/ 24 34/ 24 36/ 24 1640-KDZR 22/ 02 25 03 32/ 18 34/ 18 34/ 18 34/ 18
As can be seen in the test results, although the higher-inductance models have greater RSSI readings across the band, the S/N readings are remarkably similar for all four models (and are a more accurate indicator of actual signal strength). The lower-inductance models have a very slight drop off in S/N readings at the extreme low end of the band, while the 544 uh inductance model could not produce an S/N reading at the (out-of-band) ffrequency of 1706 kHz. Despite these minor differences, all four coil designs essentially have equal performance across the MW frequency spectrum, and all four would be very viable choices to greatly boost the DXing performance of the Tecsun PL-380 model. Detailed assembly instructions for all four coil types will be contained in the revised PL:-380 7.5" loopstick transplant article, and all four test models will be retained here for future reference.
The above test models were constructed in a serious effort to inform everyone of the actual experimental performance of the different coil designs, an effort which required significant time and expense. I feel confident that the results are accurate and trustworthy, and that I have gone the "extra mile" to promote mutual understanding. If someone refuses to accept the results, it certainly won't ruin my day :-) I have respect for those with differing opinions, but do suggest that they perform some actual PL-380 7.5" loopstick experimentation for greater mutual understanding.
73, Gary DeBock (in Puyallup, WA, USA)
. In a message dated 4/19/2010 7:19:38 A.M. Pacific Daylight Time, sdwillingham@... writes: Those of us who have measured the resonance have seen that it works correctly. Gary's later comprehensive measurements also confirm that 300uH, 400uH, and 500uH loopsticks all "track" (the 500 starts to fail a touch at the high end) and further, they all have nearly the same RSSI within a dB or two. Graham further states that his transplant loopstick has 10 dB more gain across the band, but provides no objective data for that. |
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KCBQ overloads PL-380 (Re: Tecsun PL-360 3" Loopstick Testing)
jim_kr1s <jkearman@...>
--- In ultralightdx@..., "farmerik" wrote: > Of course if your listening post is a corner of the Living room, you might hear complaints! But white nylon blends in pretty well on a white ceiling [SMILE] - FARMERIK I live alone, so no one would complain, but I'm not going there. :) 73, Jim, KR1S http://kr1s.kearman.com/ http://qrp.kearman.com/ |
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Re: Graham Maynard's Tecsun PL-380 Modification Article
jim_kr1s <jkearman@...>
--- In ultralightdx@..., "sdwillingham" wrote: > It's all a bit of a tradeoff. The PL-380 tends to have a fairly high stray capacitance on the antenna, but much of that is in the loopstick itself. I think a well-designed 450 uH inductor will reach the top of the band and 500 uH will fall a bit short. Scott, The key term is "well-designed." Spacing the turns on an external rod, as I believe Roy did, should reduce self-capacitance and let you go a little higher. Raising the gain does little to improve DX performance here though, because adjacent and on-channel pests and external noise are raised an equal amount. The stronger the signals the more AGC reduces receiver gain. That renders weaker signals inaudible, exactly the opposite of what we want. In some parts of the country it might be okay, but not here. IMO it's better to keep signal levels farther down, to gain more headroom. You can always turn up the volume, but you can't turn down the AGC (without hacking into the MCU). Improved selectivity improves S+N/N ratio and reduces off-channel interference. For DXing, I place those factors above increased gain. You folks designed the chip for use with tiny antennas, and it already has plenty of gain! What it wants is a sharp tuned circuit in front of it. > Your measurement method sounds correct to me, as long as your voltmeter or scope coupling is weak enough to keep the loading below a couple picoFarads. The HP 312B is extremely sensitive, and a short probe a foot away from the antenna is good enough. The 312B has an untuned front end, so there's no risk of mutual coupling. Someone was kind enough to give me a G8 with a defective volume control, and I'm tempted to hack in the USB port. My laptop is quite the crud generator, though, so I've been holding off. 73, Jim, KR1S http://kr1s.kearman.com/ http://qrp.kearman.com/ |
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Opinions of IDEAL inductance for MW and for LW PL-360?
Rik
If I wanted to wind an inductive loop antenna to be connected directly to the PL-360, [no lead wire, no cap] what should the values be for MW and for LW ? - FARMERIK
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KCBQ overloads PL-380 (Re: Tecsun PL-360 3" Loopstick Testing)
Rik
Just a reminder, hanging a loop from the ceiling, and having a series of attachment points allows you to tilt it without a complicated mechanism. One attachment point hangs the antenna vertical, and a few more behind it give different tilts. With a nylon swivel, made for key chains, it's easy to point, and when you are done, a hooking place on the bottom allows you to stow it horizontal near the ceiling. That is how I normally use my 4 foot loop. I only drop it down for directional work.
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Of course if your listening post is a corner of the Living room, you might hear complaints! But white nylon blends in pretty well on a white ceiling [SMILE] - FARMERIK --- In ultralightdx@..., "jim_kr1s" <jkearman@...> wrote:
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Operation Python - Final Report
jim_kr1s <jkearman@...>
Operation Python was launched in conjunction with the annual Everglades python hunt. My goal was to log 150 Florida AM BC stations by April 17, the end of python-hunting season. I added several, and fared better than the hunters, who failed to catch any exotic snakes.
http://www.sun-sentinel.com/news/palm-beach/fl-python-hunt-20100419,0,6522648.story I didn't make it to 150, though, only 141, though the project helped push my ULR total above 400 stations. The Hoop Loop project and LW DXing distracted me, and the last two new Florida stations entered the log on March 17. There are about 220 AM stations in Florida. Most of the ones I haven't heard are daytime-only, or run double-digit night-time powers. The peninsula is narrow and sunrise and sunset times are close together, which makes it challenging to sort them out. From South Florida, relative bearings to different stations on the same channel are very small, so azimuthal nulling doesn't help much. I plan to make the Hoop Loop tilt as well, which may do more good when two stations are at different distances from me, even though on nearly the same bearing. Targeted stations are showing up less frequently now that I'm scraping, but out-of-state stations on the same greyline are always welcome! A quick glance at the log shows roughly two new non-Florida stations on every channel that produced a new Florida station. 73, Jim, KR1S http://kr1s.kearman.com/ http://qrp.kearman.com/ |
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Re: Graham Maynard's Tecsun PL-380 Modification Article
sdwillingham
Jim,
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It's all a bit of a tradeoff. The PL-380 tends to have a fairly high stray capacitance on the antenna, but much of that is in the loopstick itself. I think a well-designed 450 uH inductor will reach the top of the band and 500 uH will fall a bit short. For barefoot radios, the Q of the internal stick seems to be limited by proximity effects, so if the resonance is a bit off at the high end, it might not be a big deal. So on one hand, if you want improved barefoot LW performance, you could make the tradeoff in high-MW resonance. If you have high-power locals at, say 1400-1500 kHz and want to receive weak stations at 1600-1700, however, you are asking for trouble by installing a loopstick that misses resonance at the high frequencies. It's a personal choice, as long as the correct facts are known and clearly communicated. Your measurement method sounds correct to me, as long as your voltmeter or scope coupling is weak enough to keep the loading below a couple picoFarads. Roy and I have modified PL-380s and software that measures antenna inductance, stray capacitance, and min/max frequencies within about a second. Very handy! -Scott- --- In ultralightdx@..., "jim_kr1s" <jkearman@...> wrote:
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KCBQ overloads PL-380 (Re: Tecsun PL-360 3" Loopstick Testing)
jim_kr1s <jkearman@...>
--- In ultralightdx@..., "sdwillingham" wrote: > > > To test the balance of your balun, I suggest just doing a common-mode measurement. Connect both sides of your primary (antenna side) to the signal generator. The ground of the generator to a ground plane. Connect one side of the secondary to ground and the other to your 'scope or spectrum analyzer. You want the smallest signal possible relative to the alternative of wiring the primary between generator and ground. Scott, Thanks for the suggestion. The light went on as soon as I read it. I tried a few variations of winding the primary, but the one that did best (about 15 dB better isolation than any other configuration) was with the primary turns evenly spaced around the secondary. That doesn't agree with your earlier suggestion, so I want to keep trying. A close-wound coil offset as much as possible from either end of the secondary (which would seem to give the least capacitive coupling) wasn't as good. Was thinking of winding a new transformer as a bifilar 4:1. To match the Hoop Loop the high-Z part has to be 256 uH. Not sure that will tune all the way up, but will be worth it to get a benchmark. With the loop disconnected and with the primary shorted or open, only two local stations at 1450 and 1590 get through. Those are the ones that make me want to shield the coil. Even with the secondary connection shielded, the toroid still gets plenty of signal. This is an improvement though, as before, a few other stations leaked in. One notable absentee was a pest down the road on 760. If I could knock them down and tilt-null WSB on 750, maybe I could hear KOA! I think the high-band stations are still strong because the coil's reactance is about twice as high up there. It got into sunset time so I couldn't compare null depth measurements made earlier, but my sense is they are deeper because a greater percentage of signal is coming only from the antenna. Shorting the antenna at its feed point after peaking the radio, I don't hear any additional stations. > But here's what I found out: you need to adjust the altitude (vertical tilt) of the loop to get better than a few dB nulls. Just a vertical loop will not do all that well. Chris Knight has been after me about that. I had an alt-az 4-footer in Connecticut, which was good at nulling every Nutmegger's favorite station, WTIC. Tilting the Hoop Loop last night I found a few stations where it helped, and the null of the tilt is, as you say, very sharp. Couldn't hold the antenna steady and the signals were fading, but on some stations the nulls were better than 30 dB. It'll be easy to elevate the hoop from the base and add a hinge, by extending the screw that tightens the outer hoop, so V 2.0 is underway. 73, Jim, KR1S http://kr1s.kearman.com/ http://qrp.kearman.com/ |
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Re: Graham Maynard's Tecsun PL-380 Modification Article
jim_kr1s <jkearman@...>
--- In ultralightdx@..., "sdwillingham" wrote: > Summarizing, I agree that loopsticks pushing 500 uH will be fine in MW and give some extension to LW performance. Scott, I'll summarize my measurement method because I know you'll understand it. I'll be glad to email a detailed explanation to anyone who asks. Couple a stable signal generator and a measuring device -- which can be another ULR, an rf voltmeter (I used a selective rf voltmeter also loosely coupled). or a scope -- into the antenna Tune receiver under test and signal generator to, say, 1500 kHz. Observe voltage. Leaving signal generator tuned to 1500 kHz, tune receiver under test higher in frequency. The voltage should drop as the LC circuit is tuned out of resonance at 1500 kHz. If the voltage does not drop within a few kHz, it implies that the tuning capacitance has reached its minimum and the radio cannot tune that inductor to a higher frequency. My tests with a 550-uH coil showed it could not be resonated in the upper part of the MW band. RSSI readings across the band were higher than with the stock antenna. This is deceiving, and I attribute it to higher reactance. But the peaking effect of resonance was absent. I note that coupling the antenna to a large, separately tuned loop antenna will provide the higher frequency selectivity lost by using the larger antenna coil. Any 240-uH coil I've tried peaks well anywhere from 530-1710 kHz, and that's the value I've been using for MW. As you mentioned to Stephen, a larger coil delivering more signal to the receiver on the low end of the band, where it resonates, can create a new set of problems in areas where there are more strong local stations than are found in the Seattle area, such as in San Diego, and Stuart, Florida. 73, Jim, KR1S http://kr1s.kearman.com/ http://qrp.kearman.com/ |
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Re: Graham Maynard's Tecsun PL-380 Modification Article
sdwillingham
Gary,
I have a question for Graham. Perhaps you can ask him, since you've already been in contact? This concerns the "digital noise" he mentions several times. I have never heard any substantial noise of that type even though I haven't had either of the RF shields in my radio for months. He also mentions that the noise was worse when he installed an inductor in series with the speaker. This leads me to wonder if he was testing the radio with and AC-adapter hooked up? The charger circuit has a choke near the speaker and could cause some bleed-through of power supply noise. Also, just having a cable connected can make other noise pickup worse. I think all portables will operate best with only battery power. Just a thought. I'm curious for more details on the digital noise pickup he has observed. Thanks, Scott |
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Re: Graham Maynard's Tecsun PL-380 Modification Article
sdwillingham
I have to say that an item I find irksome in Graham's article is that he substitutes a new loopstick and declares that it "tracks well" over the band. In the next sentences he implies that the original loopstick must not resonate properly and that both Tecsun and Silabs fail to understand their own designs. That he misses the proper tracking of the original shows that he is not applying an objective measurement.
Those of us who have measured the resonance have seen that it works correctly. Gary's later comprehensive measurements also confirm that 300uH, 400uH, and 500uH loopsticks all "track" (the 500 starts to fail a touch at the high end) and further, they all have nearly the same RSSI within a dB or two. Graham further states that his transplant loopstick has 10 dB more gain across the band, but provides no objective data for that. Summarizing, I agree that loopsticks pushing 500 uH will be fine in MW and give some extension to LW performance. But Graham should provide more evidence for some of his further claims, especially when he may be leading other readers to cutting up the plastic parts in their radios. -Scott- |
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Re: Graham Maynard's Tecsun PL-380 Modification Article
Hi Scott,
Thanks for your comments on Graham's article.
I'll forward your correspondence to him, and trust that he will respond
promptly. Graham's technical articles and postings are mostly limited to the
Medium Wave Circle group in Europe, and my own contacts with him have been very
limited. Since I am also an MWC member and have had several of my ULR-related
articles published in their MWN bulletin, Graham was apparently persuaded
to purchase his PL-380 as a result of my review. But his modification
article was, of course, an independent undertaking.
73, Gary
In a message dated 4/19/2010 7:51:40 A.M. Pacific Daylight Time,
sdwillingham@... writes:
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Puyallup, WA TP's for 4-19
Hello All,
It was a mediocre morning in general for Asiatic reception, although one
station did produce a vibrant signal momentarily on the 7.5" loopstick
PL-380.
594-JOAK and 747-JOIB both managed weak audio around 1248, and both 972 and
1134 kHz had traces of Korean just before the 1300 TOH. After 1300 the high band
"big guns" had fair to good audio off and on, with 1566-HLAZ producing this good
signal briefly around 1312: http://www.mediafire.com/?hm5n2twx2nw
1575-VOA also came up with decent audio shortly after 1300, but it didn't
last very long.
With the sunrise enhancement getting earlier and earlier and the resulting
TP-DX in Puyallup getting slimmer and slimmer, it may be time to shift
the focus to DU-chasing at Grayland :-)
73, Gary DeBock
Spotting receiver: Modified ICF-2010 (30" loopstick)
Main receiver: Modified Tecsun PL-380 DSP Ultralight (7.5"
loopstick)
7.5' PVC-frame tuned passive loop (in the back
yard) |
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Re: Graham Maynard's Tecsun PL-380 Modification Article
jim_kr1s <jkearman@...>
Roy,
Based on my own work, I know you're right (I guess I got another dud chip -- did all the good ones go to Puyallup and England?), and your post made the case very well. Keep up the good work, Roy; some of us are paying attention. You've been a big help to me. When you mentioned that my 280-uH internal antenna might be too large, I worked out a way to test it by measuring the peaking effect at resonance, and determining where peaking was no longer possible because the tuning capacitance hit its lower limit. I'd be happy to share details of my simple method, which needs only a stable signal generator and a second receiver with signal-strength indicator (or a scope or rf voltmeter). You can do this test on an unmodified ULR, without even opening the case! It will help you understand why resonating the coil is so important. Come to think of it, tuning a Terk, Tecsun or SAT will show you that; this test will prove whether your antenna resonates across the band. Hint: a 554 uH coil won't. Caveat emptor, folks. Unless you got one of the "good" chips, the bigger RSSI obtained with a too-large inductance comes at a price. 73, Jim, KR1S http://kr1s.kearman.com/ http://qrp.kearman.com/ |
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