[Lf] Re: monitoring on 136.745kHz for WA2XTZ

[Andre' Kesteloot]

Thanks Alan for you message. I am copying this reply to the rest of
the lf group
here (lf at amrad.org) so that they may want to comment on your idea of a
slight
frequency shift from time to time.  We use a crystal-controlled
transmitter, and
could shift the frequency by switching in and out, periodically, an
extra
capacitor across the adjustable capacitor presently in series with the
crystal.
I will await comments from other members before embarking in that
modification.

Incidentally, our beacon wa2xtf/12 located in Front Royal Virginia is
presently being heard "very loud" in London Ontario. (more than 500
kilometers)

Happy holidays and 73
Andre'
***********************

Alan Melia wrote:

> Hi Andre', you will note I have copied this to Dave G3YXM as well.
> I have been monitoring 136.75 overnight for some time with nothing heard. It
> was rather optimistic as my aerial system leaves room for improvement. I
> have just acquired a good signal generator to cover the frequency and
> started off by trying to measure the sensitivity of my receiver. The net
> result was the surprise that using Spectrogram I could detect carrier
> signals that presented just 20nV to the 50ohm receiver input. (I suspect
> that my measurement technique my need a bit a cleaning up but it should be
> good to a dB or two.)
>
> Somewhat surprised by this and knowing that my system now yields an S-meter
> reading of about 9+20dB for the well known DCF39 transmission on 138.83kHz,
> I determined to experiment with Spectrogram using 'heavy' averaging, and the
> maximum value in the 'Time scale'. This morning I was able to collect a very
> interesting chart of a section of the band 40Hz either side of the WA2XTF
> frequency, straddling the UK East Coast dawn period. There are two lines of
> interest, at a level that approximated to 10nV, one reading 136.744 and the
> other 136.745 (which I believe is the frequency of your latest beacon).
> Unfortunately, by reference to other lines on the chart, I am fairly sure
> that these two are in fact sidebands from the Loran C stations around about
> 100kHz. (Yah boo shame!) I would have kept quiet and carried on with my
> experiments, except that it occured to me that there is a message for us
> here.
>
> I am in a location where to turn my loop aerial to the USA, it is almost
> side-on to the two main Loran C sites (France and the northern coast of
> Germany) so I do not get anything like the trouble experienced by many other
> stations. There is always going to be a problem identifying the signal on
> long integration times, and distinguishing it from Loran lines. Even On-Off
> keying will not really provide certain identification as, at low levels, the
> signal peeps in and out of the noise. The Loran lines are by their very
> nature, extremely stable in frequency. I am wondering whether a very simple
> very small frequency shift, not necessarily keyed in morse, would help in
> the identification of the real beacon signal. I think probably a shift of 2
> Hz to at most 5 Hz would probably suffice, and as I use a long integration
> (averaging time) the shifts would need to be for about 60 seconds. Time
> would not be important but a regular shift  would aid recognition, and make
> the signal stand out from the Loran lines, which I suspect will be with us
> for a long time to come.
>
> Sorry to dangle the 'sweetie' and snatch it away, but I suspect from my
> calculations I may be some 10dB adrift (at least) in the rx sensitivity
> required, even if you were managing to radiate a full 1 watt ERP.  Still
> there is nothing to beat 'travelling in hope' or even 'outragious optimism'.
>
> Have you measured the current you can drive into your long wire? A comment
> to Dave re the Radcom column ....CFH is still off the air at present....I am
> hoping to get an early warning from Jon if it is planned to return.
>
> Merry Christmas both, and many Happy New Years in the new Century
> Cheers de Alan G3NYK
> Alan.Melia at btinternet.com