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New Parts for FSL and Air Core PVC Loop Antennas


Todd
 

Hi Gary, and All.

Recently an Australian DXer constructed a 135 mm diameter MW FSL using forty one Jaycar LF1010 (9 x 100 mm) ferrite rods. These rods are more affordable than anything else available on Australian eBay [1].

Jaycar Electronics Australia also sell a larger (9 x 180 mm) ferrite rod [2].

In terms of optimal FSL signal gain and Q, what is the preferable ferrite rod size to use among the two Jaycar available options? Also, how are the number of Litz wire turns calculated to provide 520 to 1750 KHz coverage for a given number of rods? A new article would be instructive factoring in the more recently available rod dimensions, and improved lower resistance Litz wire.

When I built your 40" PVC tabletop box loop design using 9 turns of wire, I fortunately chose the higher Q 8:1 reduction drive variable capacitor from Mike's Electronic Parts [3].

Any thoughts on the theory behind why certain variable capacitors offer higher Q?

Regards,

Todd

1. https://www.jaycar.com.au/9mm-x-100mm-inanimate-ferrite-rod/p/LF1010

2. https://www.jaycar.com.au/180mm-x-9mm-ferrite-rod/p/LF1012

3. https://www.mikeselectronicparts.com/product/384pf-air-variable-capacitor-with-81-planetary-reduction-drive/


Todd
 
Edited

Some updated information was kindly supplied by Steve Ratzlaff.

The current batch of available Russian ferrite rods are 400 permeability. But the desired permeability for MW is ~ 125. Fortunately, according to Steve, The Australian Jaycar ferrite rod's UI = 120 specification corresponds to the more optimal ~ 125 permeability. Hence this requires more turns of Litz wire.

These FSL antennas are more difficult to construct when factoring in the optimal number of rods, and Litz wire turns for desired ~ 520 to 1750 KHz coverage. There are many factors involved that need to be considered before purchasing materials. Kevin Schanilec's FSL optimization paper is essential reading before undertaking construction.

Regards,

Todd

AA7U wrote:

Use cheap magnet wire at first to find out the turns needed, before going to the expensive Litz wire. That will still be just an approximation not an exact thing. Big Litz of course is wider and for a given coil width will have fewer turns than wire that is thinner. All that factors into the final coil inductance. As noted, almost all FSL coils require experimenting with the actual number of turns for the variable cap being used. Main thing is to have enough inductance to tune to the bottom of the MW band.

Longer ferrite rods are always preferable to shorter rods, given a choice. The current batch of Russian rods on eBay are all 400 permeability, which is pretty high. Desirable permeability for MW is 125. If the Jaycar rods are similar to 400, then fewer turns would be needed for a given inductance than for rods with lower permeability. If they are 125, more turns are required. So once again it's all about experimenting to figure out what the Jaycar rods do.

Gary discovered a formula for FSL sensitivity relating FSL coil diameter to FSL coil width with larger diameter and longer coil length giving greater sensitivity. Generally you want the largest diameter FSL your pocketbook can afford to buy ferrite rods for.

You mention Q, but generally Q is related to the size of the Litz wire, and if the variable capacitor has good Q. Generally coil Q sets the limit as generally coil Q is lower than cap Q, if the cap is decent quality. Variable caps with phenolic insulation are always lower Q than other types of insulation; the caps Gary now prefers have phenolic insulation but apparently the manufacturing process somehow makes these with a higher Q than previously.

More turns of Litz wire gives greater sensitivity compared to fewer turns of the same size Litz for a given diameter coil. This is good. Ferrite rod coil Q is in my experience (I have an HP 4342A Q meter) much lower Q than an air coil using the same Litz. More turns of Litz may theoretically have lower Q than fewer turns of the same Litz but you are not going to notice the difference.


Gary DeBock
 

Hi Todd,

Sorry for the delayed response. Steve's detailed information is of course very accurate and helpful, and I appreciate him stepping in to comment. We have been experimental partners for over 10 years, and by coincidence, have exactly the same technical training from the US Navy.

<<<   In terms of optimal FSL signal gain and Q, what is the preferable ferrite rod size to use among the two Jaycar available options? Also, how are the number of Litz wire turns calculated to provide 520 to 1750 KHz coverage for a given number of rods? A new article would be instructive factoring in the more recently available rod dimensions, and improved lower resistance Litz wire.   >>>

Like Steve says, the number of Litz wire turns for a new FSL design will always require some final adjustment, but if you have an existing FSL design covering the MW band with exactly the same components as the proposed design (same length and permeability of ferrite rods, same type of Litz wire and the same tuning capacitor), then you can calculate the number of required Litz wire turns prior to construction by using math, and usually be within one turn of the actual number. You accurately measure the coil diameter of the existing design, and write down the number of Litz wire turns in the existing design. Then you use the math formula where the length of one turn of wire is the coil diameter x Pi (3.141) and then multiply this by the number of turns, which gives you the total length of wire of the existing design. The total length of wire of the new design should be roughly the same, so you then use a proportion where this total length of wire is divided down by the product of the proposed coil diameter and Pi (3.141). This will give you a fairly accurate estimate of the required number of Litz wire turns in the new design. Like Steve says, with very expensive Litz wire it is a Cardinal Sin to cut an FSL coil too short, because splicing Litz wire degrades its performance. So the best option is to either play around with cheap wire as Steve suggests, or to cut an expensive Litz wire coil with an extra turn, in order to make sure that you don't end up with a coil that won't tune down to 530 kHz.

I'll try to answer your other questions later tonight, Todd. Good luck in your experimentation!

73, Gary
 




Gary DeBock
 

Hi Again Todd,

<<<   Recently an Australian DXer constructed a 135 mm diameter MW FSL using forty one Jaycar LF1010 (9 x 100 mm) ferrite rods. These rods are more affordable than anything else available on Australian eBay [1].   >>>

It would be very helpful if that Australian DXer could post a design photo showing the number of coil turns, type of Litz wire, type of variable cap, type of frame, etc. Then I could simply use math to decide how to make larger and smaller sizes of that same type of FSL, using the Jaycar 9 x 100mm ferrite rods.

Using the longer 9 x 180mm ferrite rods will give more inductance for a given coil size, slightly reducing the number of Litz wire turns required to tune the same frequencies as the 9 x 100mm ferrite rod design coil.

<<<   Also, how are the number of Litz wire turns calculated to provide 520 to 1750 KHz coverage for a given number of rods?   >>>

Since I've never used the Jaycar rods I can't give you an exact formula, but the number of rods is related to the coil diameter, and if 41 rods results in a 135mm coil diameter for the Jaycar rods, you do have enough information to design a new FSL, but ONLY if you use the exact same components as the Australian DXer used (ferrite rods, wire type, variable cap type, etc.). This assumes that he was able to get 530-1701 kHz coverage with his design. You can use the math formula that I described in an earlier post, and it should get you within one coil turn of being exactly the right length. Like Steve said, you shouldn't use expensive Litz wire for rough testing; only use expensive Litz if you are sure of the number of coil turns necessary for full MW band coverage with the Jaycar variable cap (if that's what you plan to use). Any components different from what the OZ DXer used will throw off the math calculation formula for coil turns.

<<<  Any thoughts on the theory behind why certain variable capacitors offer higher Q?    >>>

Like Steve said, the phenolic insulator type of variable cap is not the highest Q type available, but for my own FSL designs (which require rugged construction to survive rough travel, and weather extremes) they make good sense. The discovery of superior performance with the "384P" variable cap (from Mike's Electronic Parts, with Oren Elliot Products being the OEM) was completely by accident. Apparently they have made some type of substitution which provides significantly higher "Q", and better gain performance. How and why this happened is a mystery, but the difference in DXing performance is pretty astonishing. All of my recently constructed FSL's use this variable cap, as well as the models given to Craig and Chris prior to the recent Kauai DXpedition.

73, Gary

 


Chuck
 

Hello Gary and all,

First, a huge thank you to Gary and the community of people who worked on this body of knowledge. The FSL is exactly what I've been looking for to complement my Tecsun PL-660 utralight.

To follow on to Todd's question, I am gathering parts to construct the 3.5" Frequent Flyer FSL and have obtained 
27 140mm x 8mm ferrite rods (instead of the specified 160mm x 8mm)
45 feet of 1162/46 Litz wire (instead of the specified 35 feet)
1 higher Q 8:1 variable capacitor from Mike's Electronic Parts (instead of the specified 365mm variable cap)

I could imagine the unit will perform fairly well simply by substituting the variable cap and ferrite rods but are there any simple "rules of thumb" about the number of turns of wire for the circuit factoring in the 140mm rods and superior var cap? 
Or are these undefined, meaning I'll just need to experiment for myself to optimize performance?

If this has been covered before, I'd appreciate a pointer towards the earlier post.
Thanks so much for the help!

Best,
Chuck


Gary DeBock
 

Hi Chuck,

<<<    To follow on to Todd's question, I am gathering parts to construct the 3.5" Frequent Flyer FSL and have obtained 
27 140mm x 8mm ferrite rods (instead of the specified 160mm x 8mm)
45 feet of 1162/46 Litz wire (instead of the specified 35 feet)
1 higher Q 8:1 variable capacitor from Mike's Electronic Parts (instead of the specified 365mm variable cap)   >>>

Wow, Chuck, by quite an amazing coincidence I have already constructed a 3.5" diameter Frequent Flyer FSL using exactly 27 of the 140mm x 8mm Russian surplus ferrite rods. I also used the 1162/46 Litz wire, and the higher Q "384P" variable cap from Mike's electronic parts. A photo of the completed model is attached.

As such, I can give you exact information on the coil turns and Litz wire length. The coil uses 27 full turns of the 1162/46 Litz wire, plus about 8 inches on each end as pigtails for soldering to the variable cap. The total wire length would be the 27 coil turns (29 feet 9 inches) plus 16" for pigtails (total of 31 feet 1 inch). The model tunes from 515-1650 kHz, and has an FSL sensitivity score (coil diameter x ferrite length) of 490. This makes it almost exactly as sensitive as the 5" Frequent Flyer FSL model taken to Poipu, Hawaii in November, which tracked down AM-DX from every continent except Europe (FSL sensitivity score of 500).

Gary DeBock (in Puyallup, WA, USA)

 


Chuck
 

Gary,
Thank so much for that, I'm glad you've already had success with the very design I'm building!

I did obtain the 140mm x 8mm rods from a different source since sufficient quantity wasn't available from the eBay seller.
https://www.rf-microwave.com/en/ferrite-rods/171/

These are Chinese made rods sold by an Italian company.
I ordered 30 of the BF-51s @ $1.83 a piece last week. The big extra expense was DHL international shipping, which was about $38 to my Northern Virginia location. I received them yesterday, they were packed well (none broke), and seem fairly straight and well constructed.
Their online inventory shows there are still 348 of these units in stock in case anyone else is interested.

Best,
Chuck


Gary DeBock
 

On Tue, May 26, 2020 at 10:01 AM, Chuck wrote:
Gary,
Thank so much for that, I'm glad you've already had success with the very design I'm building!

I did obtain the 140mm x 8mm rods from a different source since sufficient quantity wasn't available from the eBay seller.
https://www.rf-microwave.com/en/ferrite-rods/171/

These are Chinese made rods sold by an Italian company.
Chuck,

Thanks for the additional information about the Chinese-made 140mm x 8mm ferrite rods.

Unfortunately, since my  own FSL was constructed with the Russian surplus ferrite rods ordered from a seller in the Ukraine ("alexer1" on eBay), the coil turn information that I gave you may not apply to a an FSL constructed with Chinese rods. The number of coil turns is related to the permeability of the ferrite rods, and Chinese-made rods typically have significantly different permeability than either Russian surplus or Amidon ferrite rods. So you will probably need to fine tune your own antenna's FSL coil because of the Chinese-made ferrite rods. Sorry! 

If a DXer uses the exact same components that I did for my FSL antenna then he would be able to simply construct it in an
identical way, and probably come away with identical performance.

73, Gary



  


Chuck
 

On Tue, May 26, 2020 at 02:24 PM, Gary DeBock wrote:
Unfortunately, since my  own FSL was constructed with the Russian surplus ferrite rods ordered from a seller in the Ukraine ("alexer1" on eBay), the coil turn information that I gave you may not apply to a an FSL constructed with Chinese rods. The number of coil turns is related to the permeability of the ferrite rods, and Chinese-made rods typically have significantly different permeability than either Russian surplus or Amidon ferrite rods. So you will probably need to fine tune your own antenna's FSL coil because of the Chinese-made ferrite rods. Sorry! 

If a DXer uses the exact same components that I did for my FSL antenna then he would be able to simply construct it in an
identical way, and probably come away with identical performance.
Gary,
That makes sense and I totally understand that disclaimer.
The rods I obtained are rated with a permeability of 400, which I believe is the same as the Russian surplus units.
Unless there is some other characteristic to compare and differentiate them, my hope is the ones I got are electrically identical to yours.

Either way, I'll start with 27 turns and experiment a bit before permanently securing the winding. Thanks!

Best,
Chuck


Gary DeBock
 

<<<   Gary,
That makes sense and I totally understand that disclaimer.
The rods I obtained are rated with a permeability of 400, which I believe is the same as the Russian surplus units.
Unless there is some other characteristic to compare and differentiate them, my hope is the ones I got are electrically identical to yours.
Either way, I'll start with 27 turns and experiment a bit before permanently securing the winding. Thanks!   >>>

Thanks Chuck,

If it were me, and if I was cutting the expensive 1162/46 Litz wire to make an FSL coil, even if the Chinese manufacturer says that their ferrite rods are the same (400) permeability as the ones I used, I would cut the 1162/46 Litz wire a couple of extra turns longer than what I did for my existing (Russian surplus ferrite rods) FSL, to account for differences in manufacturing tolerances and measurements.

Otherwise you would need to splice the Litz wire, if you cut a coil too short (to tune down to 530 kHz). Splicing Litz wire is never recommended, since each individual Litz wire strand is designed to have its own performance potential throughout the entire length of the coil.

73, Gary

 


Chuck
 

On Tue, May 26, 2020 at 03:40 PM, Gary DeBock wrote:
If it were me, and if I was cutting the expensive 1162/46 Litz wire to make an FSL coil, even if the Chinese manufacturer says that their ferrite rods are the same (400) permeability as the ones I used, I would cut the 1162/46 Litz wire a couple of extra turns longer than what I did for my existing (Russian surplus ferrite rods) FSL, to account for differences in manufacturing tolerances and measurements.

Otherwise you would need to splice the Litz wire, if you cut a coil too short (to tune down to 530 kHz). Splicing Litz wire is never recommended, since each individual Litz wire strand is designed to have its own performance potential throughout the entire length of the coil.
Gary,
I'll definitely take your advice and cut the wire long by a few turns for experimentation.
And I'm assuming full turns only -- that partial turn winding (like 27.5) aren't valid.
Best,
Chuck