[Lf] Re: [Lowfer] Xmit antennas as receiver antennas?

[Frank Gentges]

Les,

At AMRAD we were lucky enough to get permission to connect to the unused 
Navy LF and VLF antenna at Annapolis MD prior to their being 
demolished.  We could only receive as we did not have permission to transmit.

Marconi.
This was 300 ft tall with a 700 ft horizontal top section with 3 parallel 
wires.  On listening to European LF broadcast stations we observed that the 
subjective S/N between the Marconi and our 6 foot active whip was 
indistinguishable.  Unfortunately, the static crashes did not allow us to 
make any quantitative measurements.  Signal to Noise in this context was 
Signal to Sferics.  This antenna was demolished before we could get a quiet 
night to make serious measurements.

VLF Top Loaded Vertical.
The center tower was 1200 feet tall and was surrounded by 6  ea 600 foot 
towers supporting the top hat.  On listening with this antenna we had some 
chance to measure signal and noise levels with a selective voltmeter.  NAA 
at Cultler Maine put in a +18 dBm signal and S/N was slightly over 60 
dB.  The same active antenna as before was well below this S/N.  LF 
improvements were much less but we did see some improvement.  This antenna 
made a super crystal set antenna!!

These extreme and very extreme examples show that very large receiving 
antennas probably don't add much to the signal but that is tempered by the 
sferics corrupting the observations.  On the other hand, if you were to 
construct an outrageously large receiving (transmitting if you wish) 
antenna you might get some improvement in S/N.  Obviously, the signal 
levels were higher, much higher in some cases but also the noise was higher.

  We conclude that small efield probes and loops offer much more 
flexibility on orientation and location so as to better receive LF signals 
for the LOWFer and radio amateur community.  The transmitting antenna may 
work but usually is not so well situated that a smaller receiving antenna 
cannot be better situated for better S/N

Frank K0BRA

At 03:52 AM 10/1/00 -0500, Les Rayburn wrote:


>I notice with the new Icom 746 that my transmit vertical seems to be my 
>"best" antenna
>for reception as well. Obviously, the high "Q" circuit of the antenna has 
>a lot to do
>with the increased signal levels within the lowfer band, so I'm wondering 
>if anyone
>else has used their transmit antennas successfully on skywave signals?
>
>Currently, I have a longwire (about 120 feet long), and an active antenna 
>to choose from.
>Signals on the transmit vertical are about 15db stronger than on the other 
>antennas.
>Of course the signal to noise ratio is not as good as the active antenna.
>
>
>
>Les Rayburn, N1lF
>4919 Cox Cove
>Helena, AL 35080
>XMGR 189.500Khz
>
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