Dear Dick, LF Group,
High frequency stability is needed for long duration QRSS beacon
transmissions with 60s dots, as you might use around 136.32kHz, so I should
keep the crystal oscillator for that.. But for relatively short contacts
with 3s/dot QRSS, stability can be greatly relaxed - drifting around a few
Hz does not usually make a big difference. For quite a long time, I used a
simple LC VFO for QRSS operation, which was usually adequate. I used to
monitor the TX frequency on the RX spectrogram display, and if it was
drifting too much I just tweaked it back again.
I'm not sure what your VXO does, but I would certainly give it a try for
QRSS3. Another way of generating a reasonably stable variable frequency
around 137k is to use one of the cheap 3.58MHz ceramic resonators in a "VXO"
circuit, and divide by 26 to get output in the 136k band. It is possible to
cover the whole LF band with one of these, and the one I tried would stay
within a few Hz without difficulty.
Cheers, Jim Moritz
73 de M0BMU
----- Original Message -----
From: Dick <[email protected]>
To: <[email protected]>
Sent: Friday, August 18, 2006 9:07 PM
Subject: Re: LF: QRSS QRG's
> Ok thanks, hmmm unfortunatly I am a bit late in discovering this, as I
> already made the first part of an X-tal oscillator for 136.320kHz........
>
> Well, I guess I have to start looking in my X-tal again.
> Problem is how to make 137.7 (or better 137.7x2) from
> an X-tal.
> Of course I have nothing in my junkbox that can be divided to this
> frequency, in fact
> even for 136.320 I had to manually modifiy an X-tal by opening it up and
> painting it.
>
> Anyway, meanwhile I got QRSS running!
> Now I only need to built something that creates the right fixed
> frequency....
> My VXO will reach it, but is not acurate enough , I guess.
>
> 73
>
> Dick, PA4VHF
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