http://elecraft.85.s1.nabble.com/Need-K3-dB-Measurements-on-new-160M-Antenna-tp5468244p5474258.html
I would try a chart recorder in this arrangement; there's no mistaking which
channel is which. Of course use a modern version using pc sound card then
> Alas, after years of doing A/B manual coax switch tests, I have given
> up on that exposing anything better than 10 db differences on anything
> other than stable local signals. And that is suspect because it is
> often ground wave, which bears no resemblance to sky wave.
>
> I built a 60 hz switch which used 12VAC plus and negative to
> alternately bias off left and right diodes connecting a common RF
> output port to two RF input ports. Being careful to use no AGC or
> very slow AGC, this presented an audio from the RX which showed to an
> oscilloscope the signal comparison between A and B that could be
> measured on the scope and converted to dB.
>
> I also quickly learned that I had no hope whatsoever of perceiving a
> difference less than 3 dB in my ear and didn't do all that well with
> less than 6.
>
> I used that to compare signals on various antennas and showed it to
> the owner. But so ingrained is the idea of manual A/B coax switching
> that he was back to judging results the old way, and discarding
> methods that gained a dB here and there, because "he couldn't hear it,
> and was going to trust his ears."
>
> The main problem of the device was an unambiguous way of identifying
> the port on the oscilloscope display. I have an idea of using a PIC
> device instead of the house AC to create the switching intervals, one
> which starts a sequence with a "long" A port and ends with a long B
> port and 8 regular ports in between, with a space between the two long
> ports. That would always unambiguously identify the A and B signals.
> Follow that with a program to analyze the audio levels and present
> peaks, minimums and averages for both signals and signal-to-noise, and
> you now have an antenna analyzer that can show you real differences
> between antennas real-time.
>
> To me anyway, that sounds like a tailor-made Elecraft gizmo kit. I
> think you could sell tens of thousands of those. Really surprised
> something like that not already around and part of during-contest
> comparisons between antennas.
>
> If the gizmo had the ability to decode the results and put it on a LED
> display marked with port A on one end and port B on the other, with
> the middle LED meaning equal, with two or three ranges, it would be
> the cat's meow for comparing two antennas.
>
> 73, Guy.
>
> On Sat, Aug 28, 2010 at 11:49 AM, Graham Kimbell G3TCT
> <
[hidden email]> wrote:
>> Jim
>> Afraid I can't help with listening on 160, but an interesting topic, and
>> a measurement technique applicable to other situations. My observation
>> is that the mental averaging will be rather tricky, especially if the
>> QSB is slow and unpredictable. What we need is something (software?)
>> which will record the strength seen by the K3 over a minute or 3, and
>> then provide a statistical analysis. You would then get a picture of the
>> average, peak, trough and distribution of strengths.
>> I wonder if something like this exists already - or could be included in
>> P3 s/w?
>>
>> Graham
>>
>> On 19:59, Jim Brown wrote:
>>> Crew,
>>>
>>> I've put up a pair of new antennas for 160M that are predicted to have
>>> about 3dB of gain over my existing vertical. Without going into a lot of
>>> detail, each antenna is a wire sloping off of my 120 ft tower, one going
>>> east, one going west. The tower acts as a reflector. The tower and each
>>> wire have 4 elevated radials. The antenna is working -- I've made four
>>> QSOs
>>> with VK, one with FK8, and one with FO in about two hours -- but I need
>>> to
>>> figure out if it's working better than my existing omni vertical.
>>>
>>> By doing a lot of listening, I can clearly confirm the predicted 6dB or
>>> so
>>> of front to back, but QSB makes it hard to get a handle on gain, and I'm
>>> only expecting 2-3dB. That's where the dB meter in the K3 comes in
>>> handy.
>>>
>>> My method is to key down on one antenna for a while, let you get a
>>> reading,
>>> switch to the other and do the same, then back and forth between them,
>>> again for long enough for you to get a good reading. There IS a lot of
>>> QSB
>>> on the band, so you'll need to do a lot of mental averaging. Please let
>>> me
>>> know, OFFF THE LIST, if this is something that you would like to help me
>>> with. I need reports from stations that are between about 30 degrees
>>> azimuth and 120 degrees azimuth of my QTH south of San Francisco. In
>>> other
>>> words, my antenna is aimed at about 75 degrees (ENE), and I need reports
>>> that are within 50 degrees of being on axis. I could also use
>>> measurements
>>> from KH6 of the antenna that goes in that direction.
>>>
>>> BTW -- to access the dB meter in the K3, you need to hit the Display
>>> button
>>> once, then rotate the second VFO knob clockwise until you see a reading
>>> in
>>> mV. Let the knob in that position for about 15 seconds, then rotate it
>>> one
>>> more position clockwise. Now, the dB reading will be relative to
>>> whatever
>>> the average IF output was when the knob was in the mV position. Note
>>> also
>>> that the reading goes plus and minus.
>>>
>>> 73, Jim K9YC
>>>
>>>