[R-390] Field Change No. 7, R390A

Thu, 02 Jan 2003 17:35:16 -0500

Hi,

On the last go around on this one the "supplemental spaces" came out to  =
operating next to VHF / UHF radios. Apparently the R-390's would take off
and nock out the WSC-3's or some such thing.

    Take Care!

        Bob Camp
        KB8TQ

----- Original Message -----
From: "Jim M." <[email protected]>
To: "David Wise" <[email protected]>
Cc: <[email protected]>
Sent: Thursday, January 02, 2003 2:46 PM
Subject: Re: [R-390] Field Change No. 7, R390A

> "Radios in supplementaal spaces" is probably spook-speak for classified
> listening posts.  They (whoever "they" are) would want to reduce any
> local oscillator or PTO signal emissions that could be intercepted by an
> enemy in order to deduce the frequencies being monitored.  I suspect the
> screen resistor changes helped reduce oscillator output.  Alternatively,
> it was to reduce their output to prevent interference with other
> receivers.
>
> David Wise wrote:
> >
> > I also installed FC7, and like Jim found that it decreased
> > the sensitivity, even after adjustment of the IF gain
> > for maximum S/N.
> >
> > I removed it.  If I acquired a radio or module
> > that had it, I would remove it.
> >
> > We've never found the original documentation
> > explaining the reason for FC7.  After some thought
> > about the target ("radios in supplemental spaces"),
> > I believe it was meant for less-important R-390As
> > so they wouldn't interfere with more-important
> > ones.  It obviously does not apply :-)
> >
> > 73,
> > Dave Wise
> >
> > > -----Original Message-----
> > > From: Jim M. [mailto:[email protected]]
> > > Sent: Thursday, January 02, 2003 7:27 AM
> > > To: Tom Warren
> > > Cc: Morgan, Roy; [email protected]
> > > Subject: Re: [R-390] Field Change No. 7, R390A
> > >
> > >
> > > I installed the mod. to my R-390a last year to see what would
> > > happen.  I
> > > found that it decreased the sensitivity noticeably.  By that
> > > I mean that
> > > a 40 dB test signal now read 30 dB on the carrier meter.  Not an exact
> > > test but it was enough to convince me to remove the mod.  I
> > > did not look
> > > at the more esoteric effects such as harmonics or spurs.  I
> > > like a "hot"
> > > receiver.  If it were me, I would remove the mod and go back to the
> > > original values.  Jim N4BE
> > >
> > > Tom Warren wrote:
> > > >
> > > > Anybody got clues to the intended and non-intended effects
> > > of Field Change
> > > > No. 7 to the R390A?  This is the change where R702 (screen
> > > resistor on the
> > > > PTO) and R210 (screen resistor on the 1st crystal
> > > oscillator) are changed
> > > > from 56K to 220K, presumably to reduce radiation to the
> > > outside world (so
> > > > the enemy can't listen for your PTO freq or your 1st
> > > oscillator freq and
> > > > then bomb in that direction).  My guess is that the first
> > > consequence is to
> > > > reduce the output level of each of those oscillators.
> > > Secondly, there may
> > > > be some harmonic reduction from each of those oscillators.
> > > However, what
> > > > else happens?  That is, is the sensitivity of the receiver
> > > or the intermod
> > > > performance reduced by the modifications?  Also is the
> > > birdy response
> > > > affected by the modifications (e.g., less harmonic output from those
> > > > oscillators leads to fewer internal mixer products).  Any
> > > other effects that
> > > > folks have definitely found?
> > > >
> > > > My reason for asking is that I'm working on a Motorola PTO
> > > with the 56K
> > > > screen resistor and a later Cosmos PTO with the 220K screen
> > > resistor and
> > > > wondering if I ought not to "re-convert" the Cosmos PTO to
> > > have a 56K screen
> > > > resistor.  R701, R702, and R703 are out of spec on the
> > > Cosmos anyhow, so I
> > > > will probably change them out, but if a better choice for
> > > R702 is 56K
> > > > considering that I'm not worried about the enemy direction
> > > finding on my
> > > > oscillator outputs, then maybe that's what I ought to do.
> > > >
> > > > For Tom Bridgers and Al Parker, yes, the Motorola PTO is
> > > from the Charlie
> > > > Taylor (hello Charlie, if you're out there) 390A.  AND I'VE
> > > GOT THE CHARLIE
> > > > 390A MOSTLY WORKING. HOORAY AFTER ABOUT TWO YEARS.
> > > >
> > > > Tom, W4PG
> > > >
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