Topband: Oregon High Desert report
k7tjr at msn.com
Fri Oct 12 15:31:03 EDT 2007
I fired up the receiver just before 1000Zulu this a.m. (3 a.m.) local. Specifically I was looking for the H40 that never showed but was instead treated to a rather pronounced version of the early morning high angle signal arrival effect. This effect shows up here quite often. At first I thought my temporary receiving 4 square had broken as it was showing no observable front to back on all but a few signals on the band. Normally I would see in excess of 20dB. My 90 ft. Tx vertical was receiving better on all signals. I also noted that one of the East coast stations was reporting similar observations. Later in the morning propagation shifted back and the array seemed normal again.
Later this morning I looked at a few Eznec plots of the antennas involved and if I can believe what I see there are some surprising numbers. The mini 4-square still shows 8db of f/b at 75 degrees elevation, 5.5dB at 80 and less than 3dB at 85 degrees. I did not see 8dB, I might have seen 3, maybe 6dB on the many signals measured (JA, VK, AH2, KL7, R1FJ etc.). As expected the array gain is down at these elevations by as much as 20dB as well. The received signals were still there on the 4-sq but the SNR was several dB worse (right at the system noise figure) on really weak signals compared to the TX vertical. This seems to verify the extreme high angle of arrival here on the west coast. The top-loaded TX vertical is slightly better by 10 degrees on high angle as well as being 20dB higher in output to the receiver. I really do not know the arrival angles involved but evidence keeps pointing to some pretty high angles here. I see some top-band high angle arrays with gain in my antenna future. Ahh another top-band challenge..
Lee K7TJR Oregon
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