[Premium-Rx] WJ-340A manual

[John Reed]

----- Original Message ----- 
From: <GandalfG8 at aol.com>
To: <premium-rx at mailman.qth.net>
Sent: Thursday, June 21, 2007 3:25 PM
Subject: Re: [Premium-Rx] WJ-340A manual


> In a message dated 21/06/2007 19:59:15 GMT Daylight Time,
> davidatkins50 at f2s.com writes:
>
> Hello to  the list.
>
> I managed to obtain a WJ-340A-6 vlf receiver, and I'm  struggling to make 
> the
> best of it. Does anyone know where I can obtain a  manual, handbook,
> schematic, or even an info-sheet for this receiver  series?
>
> It seems very sensitive, but there are a couple of items I'd  like to 
> tackle.
> It takes up to four hours for the L.O. to settle down. I  run my RA1792 
> with
> an external frequency standard -- even without, it is  rock-solid in
> comparison with the 340A. Has anyone tackled this on a 340A?  Is this 
> warm-up
> time normal for them?
> The tuning is very coarse; even  the "Fine-tune" is too coarse for 
> creeping
> up on a beacon signal. Am I  right in thinking WJ used a varicap, here? 
> Would
> a multi-turn pot improve  things?
> There are some rear-apron sockets that I would like to understand  the 
> uses
> of. Can anyone help?
> And finally (this time), what is the "log"  position on the mode-switch 
> for?
> Hi David
>
> I can't help with the manual, but there is a manual for the WJ 357 LF
> receiver in the group archives and I suspect they might be quite similar.
>
> This receiver is going to have a capacitor tuned VFO, as with several
> similar sets and tunable demodulators of the same period.
> It's a beautiful tuning mechanism, WJ tuning mechanics tend to be
> engineering works of art, but it's never going to match the internal 
> crystal  standard
> of a 1792, let alone anything better.
>
> When you refer to it taking four hours to settle down, is that with or
> without the DAFC activated?
> DAFC =digital automatic frequency control
>
> Without DAFC you are free running the VFO.
> The DAFC provides a correction voltage for the fine tuning, which is  very
> likely to be a varicap -- it is on my tunable demodulators anyway, and 
> that
> should lock the final digit to that shown on the DAFC switch position.
> This does of course does assume that the VFO is close enough to start with
> to be locked so worth leaving it to settle anyway.
> The DAFC control voltage is generated in the counter module and I have one
> demodulator still to be fixed where this voltage is not being generated
> properly so that might be a problem to look out for.
> Again the 357 manual should prove useful, for the concept if not in 
> detail,
> as that also uses DAFC.
>
> Can't help with the "log" position and the recent Ebay photos of these
> aren't clear enough to read what's marked on the back, but might be able 
> to help
> there if you can tell me the socket markings.

I don't think you'll find much similarity between the 340A and 357 WJ 
receivers.  The 357 is tuned with an air variable capacitor and the 340A 
with a voltage variable capacitor diode. As far as the stability of the 340A 
I found it poor compared to the 357.

John Reed