[ELECRAFT] Using XG1 to measure feedline losses

[brian]

I have been using my K2 for antenna measurements but the approach I have 
taken is to measure the AGC voltage and calibrate it against  known 
sources in 10 db increments.    The chip used for AGC has a linear 
region, or I should say linear with respect the db scale, and becomes 
non linear on the low and high signal level ends.  In any case I would 
think this would be much better with regards to repeatability than 
measuring the speaker output.

Regards,

Brian n6iz

kg4htt at juno.com wrote:

>I tested the idea tonight, and got some surprising results.  I attached
>the XG1 to a 12 foot dipole, which I taped to the center of my 52 ft.
>loop (16 X 10 ft.) opposite the feedpoint.  I used insulated wire, so
>there was not an electrical connection from the XG1 to the antenna, just
>wanted the dipole to couple with the loop.  I could distinctly hear the 1
>microvolt tone at 7.040 MHz.  Weak but clearly there.  So I turned it up
>to 50 microVolt to get a better signal to noise ratio, and hopefully
>highlight the differences between the two feedlines.  I cranked the RF on
>my K2 all the way up, but left the audio at 9 o'clock to keep the signal
>from being too loud.  I measured 9 millivolts AC at the speaker output. 
>I then swapped out the 3/8 inch copper ladder line and attached 450 ohm
>"window" ladder line.  I re-tuned the tuner to get a perfect match.  I
>then re-attached the XG-1 (I left the two wires taped onto the loop, so
>there isn't a variable there) and turned it on.  I was surprised to get a
>higher reading, 23 millivolts AC.  That wasn't what I expected.  I turned
>the XG1 down to the 1 microvolt setting and listened, and it was clearly
>louder and with a better signal to noise ratio than what I heard with the
>fat ladder line.  So I swapped lines out again and tested the fat ladder
>line again.  It was back down to the 9 millivolt AC level again...
>
>So, what did I conclude?  Well, first of all, my fat ladder line wasn't
>run the same way as the original "window" ladder line was run.  So when I
>swapped out feedlines, and re-routed the feedline, I changed two
>variables, and I assumed that my noticeably louder signal was because of
>the new fat feedline.  When I did the test tonight, I routed the window
>line the same general way as the fat ladder line.  Maybe my homemade
>ladder line, which I'm sure isn't 450 ohm, does not provide the tuner as
>efficient a match, since I'm measuring both feedline losses as well as
>the associated tuner losses when matching the antenna.  And the total
>system is what really matters.
>
>So, I'll ponder this, and re-install the window ladder line, but with the
>new routing.  My wife will be happy, as she wasn't thrilled to see the
>bigger hole in the (guest) bedroom ceiling, with two copper pipes running
>out down to my tuner.  Over the past few years she has come to accept
>black window ladder line dangling from a hole in the ceiling.  And I
>learned that the XG1 can be a useful tool to test a feedline/tuner setup.
>
>Vic
>KG4HTT
>
>On Tue, 19 Apr 2005 22:47:44 -0700 wayne burdick <n6kr at elecraft.com>
>writes:
>  
>
>>The XG1 can be connected to virtually any load without being damaged. 
>>However, if the load doesn't look like 50 ohms at 7.040 MHz, what it 
>>puts out may not be exactly 1 or 50 uV.
>>Whether you'll hear even the 50-uV signal at any distance remains to 
>>be seen. Let us know how far away you can get and still hear it!
>>
>>73,
>>Wayne
>>N6KR
>>    
>>
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