Re: Guy Atkin's Independent Testing of PL-380 7.5" Loopstick
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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.
--- In ultralightdx@..., Guy Atkins wrote:
> Hi Roy,
> I really appreciate the clear fashion in which you (and Scott) explain the
> SiLabs chip's operation! You are correct; I did not realize that the chip
> tunes for proper inductance after it detects a change of frequency; I
> thought it "senses" the inductance continuously, and displays any signal
> strength changes during the "refresh" cycle of the RSSI indicator.
> I'd forgotten about the maxim of best "Q" with a centered coil. After so
> many years of seeing stock loopsticks with factory coils positioned so far
> from center, I've not given it much thought. I like Scott's idea of starting
> coil winding right at the center, and seeing if there's any difference
> between a 330 uH and 550 uH coil.
> The purpose of the black arrow marker in my video was simply to show the
> positioning of the coil for which I had previously found to give the best
> reception. With that precise point in mind it was easier to see and hear the
> signal fall-off when the coil was shifted. However, I agree that by not
> retuning the receiver after each shift it becomes a moot point.
> Despite the flaws in the method, it still remains that I'm seeing a greater
> than 20 dB improvement over the stock loopstick, and that's excellent. If
> performance increases further with a coil at the rod's exact center, that
> will be even better.
> I'm knee-deep in finalizing Wellbrook arrays and QDFA phased array
> antennas plus other preparations for a coastal DXpedition later this month,
> so I won't be able to return to ULR radio experimentation for a while.
> However, I'm sure Gary and others will be able to follow up on your and
> Scott's suggestions soon. I look forward to reading about these experiments
> of others.
> Guy Atkins
> Puyallup, WA USA
> On Tue, Feb 2, 2010 at 2:13 AM, ultralightdx@... wrote:
> > Ultralight DX
> > 13e. Re: Guy Atkin's Independent Testing of PL-380 7.5" Loopstick
> > Posted
> > by: "Roy" roy.dyball@...
> > roy.dyball@...?Subject=+Re%3A%20Guy%20Atkin%27s%20Independent%20Testing%20of%20PL-380%207%2E5%22%20Loopstick>
> > roy.dyball <http://profiles.yahoo.com/roy.dyball> Tue Feb 2, 2010 12:56 am
> > (PST)
> > Hi Garry
> > Looking at the video of the coil being moved indicates that the all that
> > is happening is that you are moving the coil away from a peak that has
> > already been established from a previous tuning operation that has set
> > the varactors capacitance to tune the loopstick at the black mark for
> > the coils inductance at that position on the rod. It appears to me that
> > the coil was originally tuned at the black mark then moved off peak
> > before the video started.
> > You cannot expect the Si4734 to track while moving the coil because it
> > does not know the coil has moved and keeps the capacitance unchanged,
> > but you have changed the inductance by moving the coil and of course the
> > signal will rises and fall when you move the loopstick.
> > Had the radio been retuned each time the coil was moved the Si4734 would
> > have returned its varactor capacitance for the new inductance brought
> > about by the movement and really the signal would not have changed by
> > much more than about 3dbu across the rod.
> > The only time the Si4734 changes its capacitance to match the loopsticks
> > inductance is during a tuning operation and this was not done in the
> > video. The capacitance does not change automatically when you slide the
> > coil. The whole idea of the Si4734 is it is self aligning. And that is
> > why you must step off and step back on frequency every time you move the
> > loopstick.
> > It would be very interesting to see the video redone showing the method
> > described above because every time the coil was moved and the frequency
> > retuned the audio and the signal levels (within about 3dbu) would have
> > come back up.
> > We must understand how this chip works and use this chip as it is
> > designed and not copy old methods from completely different technology
> > without applying them to this new technology correctly.
> > I think there has been a misunderstanding as to the correct operation of
> > how the Si4734 works and I now that criticism can be taken the wrong way
> > especially when someone has put a lot of work into their results and
> > presented them sincerely.
> > I really believe that the video showing a peak signal on the rod is
> > incorrectly presented and had the radio been retuned between movements
> > it would have only shown how cleaver the Si4734 really is at realigning
> > itself and not a signal dropping off from an established peak.
> > Cheers Roy.
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