[R-390] Below 500 kHz mod, again?

[Michael Murphy]

John,

Never heard of this R390A sub-500 KHz mod either. The up-converter idea Bob
is talking about should work great with the R390A. Active voltage probe
antennas and active loops work fantastic with an upconverter. There are
plenty of antenna projects out there.

 In the R390A I would try upconversion to a band like 10 MHz (as the tunable
IF). A few advantages here: First the R390A is dual conversion 8 MHz and up
and that means more stability, less noise and potentially fewer birdies than
at 2 MHz where it is triple conversion. (Bob?). Secondly, 10 MHz crystals
and 10 MHz stabilized references are easy to find for your converter.
Finally, WWV lives here, so we can always "zero" everything.

Tuning will be normal - upward, that is 10.200 MHz = 200 kHz.

Of course we want to use a nice vacuum tube circuit with a 6BA6 preamplifier
and a couple of 6C4s, one as a mixer and one as the 10 MHz oscillator and
some serious tuned circuits up front. Anybody got a circuit? It seems that
everybody uses boring solid state upconverters! These usually are simple
circuits with a low pass filter followed by single or double balanced ICs
like the MC1496/1596 or the NE602 or SA612. Passive switching converters
using CMOS gates or analog switches can also be utilized. Double balanced
mixers used backwards are very effective with an active antenna ahead of
them.

Here is a simple circuit: http://jacksonharbor.home.att.net/lfconv.htm

Here is a link to a circuit which is very similar to the first LF converter
that I built back in the late 1980's. Mine was a bit simpler, but used the
diode mixer idea as shown and it worked very nicely. I think I used a 4 MHz
tunable IF.  http://www.lwca.org/library/articles/kf5cq/lfconvtr.htm

Mike Murphy WB2UID

----- Original Message -----
From: "Bob Camp" <ham at cq.nu>
To: "John Seboldt" <k0jd-l at seboldt.net>; "R-390 HF Receiver List"
<r-390 at mailman.qth.net>
Sent: Sunday, September 26, 2004 9:49 AM
Subject: Re: [R-390] Below 500 kHz mod, again?


> Hi
>
> I have seen a no change mod for the Racal 6790 but I don't think there
> is one for the R-390. The way the front end of the R-390 works it would
> be a major mechanical mod to get the poor beast running below 500 KHz.
>
> The best bet on an R-390 is to use an outboard up converter to boost
> the DC to 500 KHz band up to something like 2 to 2.5 MHz. There are a
> number of designs out there for these converters. Some of them do the
> up conversion at the antenna so they can combine a whip antenna pre-amp
> with the up converter. A bunch of the guys that show up in the archives
> here have a neat little whip pre amp they came up with. It would make
> an interesting starting point for a high performance antennal mounted
> converter.
>
> Enjoy!
>
> Bob Camp
> KB8TQ
>
>
> On Sep 25, 2004, at 8:34 PM, John Seboldt wrote:
>
> > I read and deleted the simple no-damage mod for opening up the R-390
> > below 500 kHz, before realizing that it probably would apply to my
> > R-392 also! Could somebody repost it again?
> >
> > Thanks
> >
> > John K0JD
> > Milwaukee, WI
> >
> > ______________________________________________________________
> > R-390 mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/r-390
> > Help: http://mailman.qth.net/faq.htm
> > Post: mailto:R-390 at mailman.qth.net
> > Unsubscribe: http://mailman.qth.net/mailman/options/r-390
> >
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/faq.htm
> Post: mailto:R-390 at mailman.qth.net
> Unsubscribe: http://mailman.qth.net/mailman/options/r-390