Wondering about Litz and AM Crystal Loop Radio

[metrologist]

I was considering buying some Litz wire for the radio shown in the picture, but I wonder how much difference it would really make, and what would be the minimum number of strands to even consider? 10 strands is relatively cheep, but 660 is starting to get pricey, and from a practical sense would I even be able to notice?

I built that radio a couple years ago with stranded and insulated phone wire. It is 15 wraps around a 24" form. I forget what the split is, maybe 11/4 or 10/5, and I think I wound the shorter coil with the diode in the opposite direction. It works well and was peaking over 24µA on a strong station. I marked 14 stations on a wooden knob that I carved. I liked this radio because it did not require a separate antenna nor a ground, and it is very directional. I was considering adding a trap on each side (single coil with air cap on the same form) to help null the stronger close-by stations. Since, I've added a couple brass posts with knurled thumb-nuts to hold a few different diodes I've collected.

What do you think?

[metrologist]

I've added a basic schematic of what I've decompiled from the build. I do not know the capacitance of the dual gang air variable cap. There is a larger and smaller section and probably in the range of up to 400pF and 200pF, respectively. I tried several configurations of these elements and remember capacitively coupling the driven circuit seemed to increase output level and increase weak signal, but also brought up the noise.

I imagine every possible configuration has been tried, so does anyone recognize if this circuit resembles anything else well known or familiar?

[Yansi]

Living almost in the shadow of an 3/4 MW  SW transmitter, I can play a "crystal radio" with a generic 32ohm speaker with not much effort at all. 

[Tac Eht Xilef]

I built that radio a couple years ago with stranded and insulated phone wire. It is 15 wraps around a 24" form. I forget what the split is, maybe 11/4 or 10/5, and I think I wound the shorter coil with the diode in the opposite direction.

I've added a basic schematic of what I've decompiled from the build. I do not know the capacitance of the dual gang air variable cap. There is a larger and smaller section and probably in the range of up to 400pF and 200pF, respectively. I tried several configurations of these elements and remember capacitively coupling the driven circuit seemed to increase output level and increase weak signal, but also brought up the noise.

I imagine every possible configuration has been tried, so does anyone recognize if this circuit resembles anything else well known or familiar?

I'm guessing this post is yours from a couple of years ago (same pic)? It gives the #turns / turns ratio & tuning cap section values.

Apart from that, it looks like a version of the "Schmarder 1958" from Dave's Homemade Loop Antennas site.

Re: Litz wire - I'm not so sure it does make an appreciable difference in high aspect ratio, single-layer, flat-wound loops like that, though plenty of people will say it does (it does make a difference in lower aspect ratio & multi-layer coils though). I've never compared 2 otherwise identical loops with Litz vs normal #30 wire side-by-side to test my opinion though. I do know it's not that hard to build a tuned MW loop out of #30 & end up with too narrow a bandwidth for good AM BC reception, so I suspect Litz wire - if it does in fact make much difference in that sort of winding - would be even worse in that respect...

[metrologist]

That looks familiar, and I think it is different than Dave's design, but surely there was much web influence. Thanks for the info, then I think I'll put it back on the mantle as-is.

I had a few other basket weave designs I was trying as well and this one just seemed easier/better. I always admired the Lyonodyne.