[Lowfer] e-probe vs loop

[Garry Hess]

Hi Bill,

Thanks for the comments.

My loop has 20+ dB nulls orthogonal to the main beam. More careful 
construction could yield 30+ dB nulls, but what I have has proven 
helpful for decoding certain DGPS stations. Often there are at least two 
strong co-channel signals present sufficiently orthogonal that one can 
be nulled out. Ideally the e-probe is omni-directional but mine is 
within perhaps 75' of a 65' Rohn foldover tower and perhaps 50' of a 
triband beam roof tower. Both are higher than the e-probe and thus might 
influence it. However, the 9 stations I monitored so far are spread 
around in heading and all of them fared better on the loop. The loop is 
fairly isolated although there is a Linden tree within about 50'.

I normally transmit a pair of hifer signals around 13.555 MHz. The one 
radiating from a horizontal dipole is close to the e-probe, the one 
radiating from a vertical antenna is close to the loop. Although they 
don't seem to produce noticeable spurs at LF they are turned off during 
data collection.

The e-probe receive lineup is as follows: Clifton Laboratory Z1501 
e-probe, 100' of cheap RG58 coax, homebrew common-mode choke, Z1203 DC 
power coupler, 6 dB resistive splitter, 10 dB pad, SDR-IQ#1 externally 
clocked and locked to GPS, Dell E521 Windows XP computer#1.

The loop receive lineup is as follows: 10' shielded loop and preamp a la 
VE7SL, 100' 9913 cable, homebrew DC inserter, SDR-IQ#2 internally 
clocked but well calibrated, Dell E521 Windows XP computer#2.

SpectraVue version 3.00 runs on both computers and inputs data to 
Spectrum Laboratory version 2.76b8 via a USB driver and virtual audio 
cable. Text file export is programmed to save signal and noise powers in 
a 100 Hz bandwidth for spreadsheet post-processing. Carrier signals are 
centered at 400 Hz and a SpectraVue filter covering 200-1200 Hz is used. 
The Spectrum Laboratory FFT settings are size=32768 with unity 
decimation. This yields a noise equivalent bandwidth of about 0.5 Hz and 
covers through 5.5 kHz.

Because both the hardware and software are so identical I don't expect 
there to be any significant measurement differences. But it's easy to 
swap antennas and confirm that for certain. If there is an issue I can 
switch between antennas and use a single setup but then the data would 
not be quite simultaneous.

-- 
73, Garry, K3SIW, EN52ta, Elgin, IL