As I have mentioned in earlier posts, I am installing a reversible Beverage
system (480ft long) made by DX Engr. I am using the 75 Ohm RG-6 "type"
flooded coax, recommended by DXE for the feedline. I live in a very rural
area in South Carolina (all of the utilities are underground, and I am not
aware of any nearby AM stations).
I now have the feedline run from my shack to the feed point of the antenna.
I have not yet installed the feedline choke. Before I connected the
feedline to the antenna, I terminated it with a 75 Ohm load, and then went
back to the shack to look at some noise measurements. I have a panadapter
made by LP-Pan using NaP3 software. The panadapter is not calibrated, so
the measurements are only relative.
My rig is an FT-dx5000. I turned off the amp and set the rig for CW (the
bandwidth is 500 Hz.) The rig has a switch on the front panel that allows
me to connect and disconnect the Beverage antenna (just the feedline at
this point).
With my rig tuned to 1.9 MHz, and with the display averaged over a 1/2
second period, the display, and the digital readout was about -140dBm
(remember, this is not a calibrated system). Then, when I connected the
feedline, I saw no change in the noise level and the digital reading stayed
approximately the same. Also, listening to the noise, I could not detect
any change in volume. I tried the same experiment but with the frequency
set to 3.8MHz. I got the same results. Does this sound reasonable or do I
have a problem in my measuring approach?
Next, I couldn't wait any longer, so I connected the ladder line to both
the feed point and the reflection unit. I also connected the feedline to
the appropriate termination unit. Each end is only grounded with 1 ground
rod and the ladder line is just laying on the ground. (As time permits, the
ladder line will be supported at about 5 feet along its length and the
grounding will be greatly improved.)
I tuned my rig to a local AM commercial station (at 1.25MHz) and the
carrier read -90dBm (my rig's S-meter read about 10dB over S9, the
"S-Meter" on the panadapter read S4) with a bandwidth of 9kHz. I could
clearly understand the transmission. When I switched out the antenna
(without changing frequency or bandwidth) I measured -155dBm and could only
hear noise. I tried reversing the direction of the antenna, but couldn't
see or hear any difference.
Finally, I re-tuned to 1.9MHz CW and read -155dBM with the antenna
disconnected. When I switched in the antenna, I saw a very strange effect.
The noise "pumpted" from -155dBm to about -145dBm. The noise level, with
no discernible signal, and from 1.82 to 1.98MHz, would rise and fall about
every second (the time was not consistent, nor was the amount of increase
in signal level). I saw this pumping effect at 3.8MHz with a power
variation of about 15dBm.
Does any of this make sense, or am I just seeing artifacts of my panadapter?
Thanks again for all of the help so many of you have given me as I slowly
work into 160M.
Wayne, KK6BT
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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