[R-390] Frequency meter

[David Wise]

Theoretically, yes.  It's harder than it sounds.

Within any one 1MHz band, it's easy to snoop the
VFO output, and there are companies selling display
modules just for this purpose, which can be programmed
with an offset to account for the target receiver's
frequency changer topology.  However, in addition
to not giving the full story, this ignores the
inevitable inaccuracies in the 1st and 2nd crystal
oscillators, which vary from band to band.  This is
the main reason the radio contains a 100kHz marker.
To get a true readout, you'd have to snoop all three
oscillators and either mix them, or measure each and
combine the results digitally.  As a compromise (the
best possible one to my way of thinking), you could
read the VFO alone, provided your readout module had
a "Cal" button to press after calibrating the radio
when you change bands.  This button would cause the
readout to snap to the nearest 100kHz value.  I doubt
there is a pre-built module that does this, but it
would make a *very* interesting project.

There are a few R-390x variants out there that
bring all three oscillators out to the back panel,
so at least you wouldn't have to hack the radio,
but you'd still have to combine them, and in any
case you will have problems with RFI unless you're
very careful with shielding.

73,
Dave Wise (SWL)

> -----Original Message-----
> From: Charles B [mailto:ka4prf at us-it.net]
> Sent: Wednesday, September 01, 2004 6:37 AM
> To: r-390 at mailman.qth.net
> Subject: [R-390] Frequency meter
> 
> 
> 
> Is there any place inside the R-390A where a frequency meter 
> can attached to get a frequency reading?
> 
> Chuck
> 
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