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
[EMAIL PROTECTED] 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 <[EMAIL PROTECTED]>
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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