We are still in the midst of a power outage here after a severe storm
(100 Km/H winds) Sunday evening. It is now 39 hours with no mains
power in this area. I have been able to do some comparisons of the
Mini-Whip vs two series-connected orthogonal loops favoring
Europe. Bottom line is both antennas perform well but when looking
at DHO38 there is an estimated 5 dB SNR advantage using the
loops. That's consistent with the directional gain of the loop
configuration. On both antennas I see big baseline excursions (+/-
10 dB) lasting about one second. Can't be caused by local QRM
because the mains power is off all along the road here. It looks
like static crashes. Apparently I have some coupling capacitors in
the preamps which are too large for the frequencies of
interest. There isn't any visible effect on SL's waterfall because
I'm not displaying such low frequencies, but I'll be looking into
it. Maybe some voltage clipping would prevent high amplitude static
impulses from having any major effect on the output lines? Not too
serious because everything still stays within the allowable range for
sound card inputs and there is no clipping. I'm using an HP netbook
with integrated "IDT High Definition Audio Codec" - unfortunately
there is only one audio input available on the netbook (intended for
a microphone) and it's mono. Oh well...
Bill VE2IQ
At 09:50 PM 7/16/2011, VE2IQ wrote:
At 10:21 AM 7/16/2011, Stefan wrote (about Mini-Whip):
Maybe it works near the trees too. The signal level will be
reduced, anyway it might be OK as long as it is well above the
soundcards noise. On VLF this is easily done.
I found a good spot for the Mini-Whip - just above the roof of a
garage about 100 feet from the shack. Didn't want to damage the
coax jacket so instead of grounding the shield DC-wise I wrapped a
bunch of turns of solid copper house wire around it (about a foot
along the coax) and grounded that (directly below the
mini-whip). Apparently the capacitive coupling is sufficient but
your mileage may vary.
I'll let it run overnight updating the grabber. Will replot the
DHO38 SNR tomorrow.
|
