Re: Guy Atkin's Independent Testing of PL-380 7.5" Loopstick

Roy <roy.dyball@...>


When I ordered My Amidon rods 4,6,7.5" rods I also ordered 40/46, 165/46 and 630/46 (my mistake it is not 660) wire. I set about winding coils on all of the rods with different wire. After reading Ben Tongue article I was connived that the centre of the rod was the best part to wind the coil. Also knowing the Si4734 just adapted to the coil as long as it was in the inductance range specified in the chips notes this reinforced my belief to wind my coils in the centre to have the best Q.

Every time I moved up a rod or a wire size the results got better. I did not use the 630 strand Litz on the 4 or 6" rod as there is not enough room. Just like if you built a bigger aeroplane with a longer fuselage you would not use the wings from a smaller aeroplane to lift it, so it seemed to me to be the same that the wire size should be increased with rod size.

The DC resistance of the 630 Litz coil is so low that I can't read it. The same resistance associated with the same inductance of a 40/46 coil is a few ohms. So this must improve the Q for a start. My theory is that the larger wire size enables more of the rod to be covered by the coil thus enhancing the magnetic couple I don't know if it is specifically the Litz but maybe it is just the wire size, but I really would not consider using any other wire than Litz at that diameter.

I have been using the 630 Litz coil now for many days listening to distant overland stations as the sun comes up. I just rewound the 81 turn 40/46 coil slider coil to test it again. The 630 Litz coil when judged from a listening point of view reminds me of my Sony 7600GR with a good low noise floor with the signal coming out of and returning to the noise floor gently, plus the soft mute did not seem to bug me as much. On the other hand the 40/46 coil seemed to pick up more hash from the radios display creating a buzz noticeable at some frequencies along with the polling request for the RSSI and S/N indicators. I advise all members to experiment for themselves with a bit of wire and some rods. That's what the fun of ULDXing is and I hope we can all calmly disuses our results.

This points out that for the purest; at least two separate loopstick coils should be at hand. One for the top of the band and one for the bottom of the band.

Cheers Roy.


--- In ultralightdx@..., "thinkdx" wrote:
> Hi Roy, Yes, I checked mid and high band signals too, and observed the
> average reading over one minute. Any frequency I tried showed
> improvement with the coil at the same approx. position from the end of
> the rod (about 1-5/8", where inductance was 532 or so). As you
> mentioned, the improvement is not as great when you tune up in
> frequency. I made the video with 530 kHz, because there are steady,
> weak TIS stations audible on 530 from my location. I suppose I could
> have shown the effect in the video with other frequencies besides low
> band. Thanks for the tip on the high strand count 660 Litz. When I made
> an E100 slider a couple summers ago, I used 172/44 Litz, but have never
> tried any variety approaching 660 strands. Do you feel that the number
> of strands affects the noise level, or does it have to do with the coil
> wound in the middle? 73, Guy Atkins Puyallup, WA USA
> --- In ultralightdx@..., "Roy" roy.dyball@ wrote:
> >
> >
> > Hi Guy
> >
> > I noticed in your test that you had your radio tuned right at the
> bottom
> > of the band (530Khz).
> >
> > I agree that with the same 81 turn sliding coil connected to my
> PL-380
> > that it showed an increase of about 20dbu and more importantly that
> the
> > S/N had risen by some times up to 10-12db on the low frequency end of
> > the band. These results are undeniable and improve the radio greatly
> >
> > Did you get a chance to try stations at the top of the band? My coil
> > started to drop off above 1200Khz and at the top of the band showed an
> > increase in dbu of only about 7-10 and no increase in S/N level.
> >
> > I also concur that my best results have been with coils wound in the
> > centre of the rod. Extensive testing with different coils wound at the
> > centre of the rod and different wire size and inductance has shown me
> > that a value of inductance in the range 0f 330-350µH works the best
> > over the entire band.
> >
> > I found that a coil of 70 turn (110mm) 660 Litz wire wound at the
> centre
> > performed the best overall and had the least amount of noise. When the
> > varactor values are read from the Si4734 chip with it tuned to 1710
> Khz
> > it reports a value of around 10pf indicating the chip has not run out
> of
> > capacitance at the top of the band. The inductance could be increased
> if
> > you dont want to work the top end of the band.
> >
> > The Welbrook range of gear looks like good gear and I hope your DX
> > expedition goes well.
> >
> > Cheers Roy.

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