Frank Gentges gentges@itd.nrl.navy.mil
Fri, 24 Dec 1999 15:28:22 +0000 (GMT)


I got caught!  Indeed I ment Australians and you in particular because of 
the unique and interesting work you are doing.  Difference Frequency 
Keying seems to be a good way to go for low S/N and I for one would like 
to try it vs. BPSK.  I have looked at a 2 element version with 4 bits per 
element and 8 bits/one byte in two element times.  Also use two different 
tone libraries between the 2 elements to be able to differentiate the 
first and last half.  Just paper here.  Think about it, A .jpg via LF 
using DFK in only a few days!

Your CFA looks like your taking advantage of local geography.  AMRAD has
put up a 1600 foot wire horizontally through the woods and terminated it
in a ground rod in a lake at the far end.  At the near end to the AMRAD
member's house we used a 300 foot well casing for ground.  Impedence was
measured using an audio oscillator, an oscilloscope as a voltmeter and a
clamp on current transformer as a current meter with the scope.  (A
ferrite torioid would work fine here, clamp on is a luxury.) We could see
the voltage and current waveforms come into phase at resonance.  We had to
put two loading coils into the wire to tune it to 136 kHz.  You may find
the scope and current transformer approach usefu to charaterizing the
Cliff Hanger Antenna.  Once measured we had a much better idea on how to
resonate it and get the 200 watt transmitter to deliver power.  I want to
write an article on all this and add it to the web page. It was tested 
for receivng and worked quite well.

I enjoy your web pages and when I start adding links I will put yours up.

Merry Christmas

Frank K0BRA

On Fri, 24 Dec 1999, Steve Olney wrote:

> G'day,
> First a small point.  Under the heading "What are the Europeans doing" 
> on:-
>  http://www.amrad.org/projects/lf
> you have the following text:-
> "the Germans, the Swiss and the Australians, ..."   Being too far away to
> be part of Europe you may have confused us with the Austrians.
> As far as weak-signal techniques go you may be interested in work I have
> been doing for over a year now using a technique I call Frequency
> Difference Keying (FDK) and other narrowband experiments and a novel
> antenna I dubbed the CHA at:
> http://www.zeta.org.au/~ollaneg/lowfer.htm
> 73s Steve Olney (VK2ZTO/AXSO - QF56IK : Lat -33 34 07, Long +150 44 40)
> =============================================
> LowFer URL:
> http://www.zeta.org.au/~ollaneg/lowfer.htm
> AXSO LF Experimental Station URL:
> http://www.zeta.org.au/~ollaneg/axsoextx.htm
> LF Receiving - FRG-100, CHA antenna
> LF Transmitting - 177.5/177.4kHz 8W - 7.6m vertical or CHA
> Modes - AM, SSB, PSK31, SSTV, Hellschreiber, QRSS
> and a new experimental mode - FDK.  See this URL for more:
> http://www.zeta.org.au/~ollaneg/FDK.htm
> =============================================
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