I am still working on my new Beverage antenna.
I have run about 400 ft of F6-type flooded coax from my shack to one end of
my Beverage antenna. My question is: do I need to install a feedline
current choke about 20 feet from the end of the Beverage antenna (the
current choke would have its own separate ground.
To try to answer this questions, I have terminated the feedline with a 75
Ohm termination. I then tuned by rig (Yaesu FT-5000) to 1.9MHz. With no
other antennas connected to my rig I can connect and disconnect the
feedline from my rig with a push of a button on the front of the rig.
My receive bandwidth is set to 500Hz and I chose the middle of the day
because I heard it is often the most quiet time for 160M.
Simply by listening to the audio noise coming out of the speaker, I can't
detect any change when I switch the terminated feedline in and out.
Next, I turned on my Panadapter and displayed the frequency spectrum from
1.8 to 2.0MHz. The Panadapter is calibrated using and Elecraft XG3 RF
signal source. It reads -134 dBm when the feedline is switched in and out.
Finally, I connected my Fluke true reading RMS multimeter to the audio
output jack of the rig. The average reading (the averaging is done by the
meter) reads 17.1mV without the feedline connected to the rig. With the
feedline connected to the rig, the meter reads 17.2mV.
It would seem the first 2 measuring techniques indicate that there is no
common mode noise coming from the feedline.
On the other hand, the third technique, using the multimeter, seems to show
some difference. However, I'm not sure if the multimeter is responsive to
the wide range of frequencies that must be present in the noise.
I would really appreciate comments on how to measure noise and if any of my
3 techniques are valid. Is there another piece of equipment that would
give me more accurate results?
Also, I live in the country, with all utilities underground. Does -135dBm
seem like a reasonable noise figure for my location?
Thanks for all of the help you have given me to date in slowly working into
the world of 160M.
Wayne, KK6BT
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