[Elecraft] Need K3 dB Measurements on new 160M Antenna

[David Gilbert]

Why not just use the two receivers in the K3 ... one using the main 
antenna port and the other using the RX antenna antenna port.  Take the 
output from the LINE OUT port and feed it into a computer sound card to 
record the resultant audio in stereo.  You can then compare anything you 
want by looking at the waveforms side by side in an audio editor 
(Audacity is free) with a db scale.  The comparison will be almost 
instantaneous, and if you use a tone for the signal you can take out the 
noise using a bandpass filter in the editor.  If you don't trust the 
receivers to be identical, run the test both ways.   If you run the 
recorded file through Spectrogram you can expand the db scale for 
whatever precision you want.

73,
Dave   AB7E

>> 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.