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 you can squash up or expand the results for examination.
David G3UNA > 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 > <[email protected]> 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 >>> >>> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
