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Gary's New 6" FSL Design


Todd
 

Hi Gary,

Your new 6 inch FSL is a step towards higher gain in a relatively small package. I look forward to a YouTube review.

Regarding 1162/46 Litz wire used in the 6" FSL, what is the cheapest source of supply that you have found so far?

On AU eBay, 1162/46 Litz wire is quite expensive. Assuming 19 turns in your design, when I build one, there should be at least 1 or 2 extra turns to allow ferrite rod permeability variation.

21(6 x 3.1416) = 396 inches or 33 feet of wire.

The cheapest 1162/46 Litz wire on AU eBay is US $88 for 60 feet. No smaller minimum 33 feet length is available.

With tank coil Q > 500, the bandwidth will average only 2 KHz or less. The audio fidelity will be compromised as a result. Resonant tuning peak will also be sharper. Higher Q = narrower RF signal bandwidth, degraded high frequency audio response, but high signal strength when tuned to resonance.

During the process of testing various early design FSLs, what did you find by using lower resistance wires regarding varying degrees of S/N readability, bandwidth, and audio quality? For an air core loop with 1000 Q, the audio will be quite muffled at 531 KHz.

Regards,

Todd

https://www.ebay.com.au/itm/Litz-wire-1162-46-for-Amateur-Crystal-Radio-coil-Single-layer-insulation-60/153541573281?hash=item23bfca7aa1:g:aT0AAOxyTjNSdFlQ


Gord Seifert
 


   Hi guys. I am mainly a lurker here but this post forces me to ask a question. If the Q of the 1162 strand Litz is bordering on too high, why not use 660? The price of 100 ft. of 660 is about the same as 60 ft. of the 1162. The description of the 660 lists ridiculous Q numbers, even with about half the strands, although I have no idea how that would directly compare to the 1162 since he doesn't mention testing Q with 1162. Nor do I know how they would compare when used to create an FSL.

https://www.ebay.com/itm/Litz-wire-660-46-for-Crystal-Radio-coil-Amateur-Single-layer-insulation-60/160428065987?hash=item255a4204c3:g:CM0AAOSw5VFWMEL1&redirect=mobile

   Regards,
   Gord 
 


Gary DeBock
 

On Thu, Jul 2, 2020 at 08:09 AM, Gord Seifert wrote:
Hi guys. I am mainly a lurker here but this post forces me to ask a question. If the Q of the 1162 strand Litz is bordering on too high, why not use 660? The price of 100 ft. of 660 is about the same as 60 ft. of the 1162. The description of the 660 lists ridiculous Q numbers, even with about half the strands, although I have no idea how that would directly compare to the 1162 since he doesn't mention testing Q with 1162. Nor do I know how they would compare when used to create an FSL.
Hi Gord (and Todd),

Todd, thanks for your interest and questions about the new 6" FSL design, which I plan to answer in detail within a day or so.

Gord, 660/46 Litz wire was actually used in all of the most sensitive medium wave FSL antenna designs from 2011 until 2014, when the new 1162/46 Litz wire first became available. As such, all of the DXpedition FSL's (and long range AM-DX results) from 2011-2014 were based on this Litz wire.

After the new 1162/46 Litz wire became available in 2014 it was substituted for the 660/46 Litz wire in a few FSL test models here, and direct A/B signal test comparisons were made on weak signals received by otherwise identical FSL models. The 1162/46 Litz wire models always significantly outperformed the 660/46 models in weak signal reception, to the extent that 660/46 Litz wire was never again used in any of my new FSL designs. The new 1162/46 Litz wire has been one of deciding factors in the success of the new "Frequent Flyer" overseas DXpedition FSL models, which have received AM-DX at over 8,000 miles in places like Hawaii and the Cook Islands.

Of course the high cost of 1162/46 Litz wire is a drawback for many experimenters, not to mention the 60-watt soldering iron required for proper installation. 660/46 Litz wire will certainly be more sensitive than 330/46 Litz wire or something smaller, and unless a fanatical DXer needs the best possible reception in the smallest possible FSL (like for overseas traveling), 660/46 Litz wire is acceptable for most hobbyists. I have never run "Q" tests to compare the performance difference between 1162/46 and 660/46 Litz wire, but the audio signal reception difference between the two was clear enough to make a permanent believer out of this FSL fanatic. If you have any doubts about its performance, feel free to watch the 3" Baby FSL demo video, where it boosts an S3 fringe signal into an S9+ overload  https://www.youtube.com/watch?v=JZtYli09mTg&t
          
Gary DeBock (in Puyallup, WA, USA)

  


Gary DeBock
 

<<<   Hi Gary,
Your new 6 inch FSL is a step towards higher gain in a relatively small package. I look forward to a YouTube review.   >>>

Thanks Todd,

The master plan behind this new 6" FSL design was to use all the high-Q components discovered in the compact, airport-friendly FSL experimentation and combine them with powerful ferrite gain. The performance results do seem worthy of the effort, and I'll try to post a demo video soon.

<<<   Regarding 1162/46 Litz wire used in the 6" FSL, what is the cheapest source of supply that you have found so far?   >>>  

I always use the 1162/46 Litz wire from the eBay seller "Mkmak222," which runs US$1 per foot. Of course this is pretty expensive for the average experimenter, who will need about 32 feet to make a Medium Wave FSL, not to mention the 60-watt soldering iron required for proper installation. There are many cheaper varieties of Litz wire available such as 660/46 and 330/46, and unless a DXer absolutely needs the highest sensitivity in the most compact antenna (such as for overseas air travel, etc.), the cheaper Litz wire is OK in most applications.

<<<   On AU eBay, 1162/46 Litz wire is quite expensive. Assuming 19 turns in your design, when I build one, there should be at least 1 or 2 extra turns to allow ferrite rod permeability variation.
21(6 x 3.1416) = 396 inches or 33 feet of wire.    >>>

Yes, 33 feet would probably be the minimum safe length of 1162/46 Litz wire to use for an MW coil if you are not sure how all the manufacturing differences will shake out in the final tuning range. It's no fun to wind an MW coil, and then find out that it won't tune down to 530 kHz because your variable cap doesn't have as much capacitance as your previous model.

<<<   The cheapest 1162/46 Litz wire on AU eBay is US $88 for 60 feet. No smaller minimum 33 feet length is available.
   >>>

Yes, this type of Litz wire should be reserved for fanatical DXer projects, in which you tweak a tiny antenna into an outrageously sensitive, ridiculously effective gain monster for the tiny size. I've posted a 3" Baby FSL video to show this effect. But the expense of this Litz wire is steep, and probably unnecessary unless you absolutely must have a tiny little DXing "firecracker."

<<<   With tank coil Q > 500, the bandwidth will average only 2 KHz or less. The audio fidelity will be compromised as a result. Resonant tuning peak will also be sharper. Higher Q = narrower RF signal bandwidth, degraded high frequency audio response, but high signal strength when tuned to resonance.   >>>

All certainly true, Todd. The highest "Q" FSL antennas have the narrowest bandwidth, which causes some loss of high frequency audio from a DX station. This compromised audio can be somewhat improved by audio processing software, but a razor-sharp-tuning FSL antenna will always clip off some high frequency audio when its frequency matches that of a weak DX station on an Ultralight radio. It's part of the game, and you learn to use the audio processing software to compensate.

<<<   During the process of testing various early design FSLs, what did you find by using lower resistance wires regarding varying degrees of S/N readability, bandwidth, and audio quality? For an air core loop with 1000 Q, the audio will be quite muffled at 531 KHz.   >>>

The early FSL's had pretty low Q, wimpy sensitivity from their smaller Litz wire and relatively good audio from the Ultralight radios. The latest high Q gain monsters sacrifice some audio quality in an all-out pursuit of the highest sensitivity, and their 1162/46 Litz wire will drain your bank account. But all is forgiven when an S9+ Kiwi DX signal thunders across the ocean at over 7,000 miles when you are on an ocean side cliff-- especially one which rarely shows up at all on a flat ocean beach.

Gary



 

 

    

         
   


Todd
 

Thanks Gary for the detailed response.

When endeavoring to obtain the highest resonant signal output at a given frequency, the Q needs to be high as practicable. The audio fidelity will be somewhat compromised, but this can be partially improved by slightly tuning the FSL antenna to peak 1 or 2 KHz above the carrier frequency. This is why the 8:1 reduction drive is essential. 

High Q FSL antennas are the only way to obtain similar RF gain and selectivity in a small package that favorably compares to large 4 - 6 foot air core box loops. This means a 6 inch FSL can be positioned pretty much anywhere within the house. A 6 ft air core box loop positioned on the kitchen bench top is not practical. But a 6" FSL would easily sit there.

The 6" FSL with 1162/46 Litz wire will likely be more expensive for DXers outside the USA and China. I estimate the total cost for me would be around AU $250 including parts postage.

For those DXers that seek weak signals only 9 or 10 KHz adjacent to very strong locals, the high Q FSL is ideal from a 3 dB bandwidth perspective. The disadvantage is no tilting provision for reducing local signals by > 60 dB. This Kiwa loop tilting mechanism was very good for obtaining the critical tilt angle for nulling a local signal.

One possibility is to video a 6" FSL comparison test against the large 9 foot air core loop. If the results are comparable, that will be an amazing achievement in itself. Interesting to see what your most distant daytime MW groundwave signal that can be obtained with both antennas.

Regards,

Todd