[R-390] Digital readout

[Mark Huss]

It has been thirty years, so my memory is a bit hazy. It used LED 
seven-segment display like the ones you used to see in calculators. It 
had 8 digits and read to 100 Hz.
Counting was interesting, as this was before Large complexity TTL. It 
tapped the three Local Oscillators, then used analog mixing to derive 
the tuned frequency which then was counted using TTL logic. If anybody 
is interested historically, I can ask my brother if he remembers more. 
But the modern way to do it is to use the DFD2 frequency display. This 
allows three inputs good to 35 MHz to monitor the 1ST, 2ND, and 3RD 
LO's. Alternately, you can monitor 2ND LO, 3RD LO, and the BFO, then use 
a level detect to detect 1ST LO on or off fed to the counter as a logic 
level. The guy who runs AADE.com has expressed interest in modifying his 
code to accomidate the R-390A. Note, for R-390 you must measure 1ST, 
2ND, and 3RD LO. This would work on both R-390 and R-390A with no change.
One problem we are beginning to have is crystal aging. Originally, you 
rarely had to calibrate the display when changing bands. After 50 years, 
you sometimes have a variance of several kHz.

Cecil Acuff wrote:

> Rich do you remember if it was a mechanically driven affair? I am 
> assuming not if it didn't require calibrating it must have somehow 
> monitored the various frequencies and did the math necessary to be 
> accurate...
>
> Sure would like to see one of those....that's something we could 
> probably duplicate pretty easily. You would think there would be 
> technical documentation around on it somewhere....
>
> Cecil....
> ----- Original Message ----- From: <richardmay01 at comcast.net>
> To: <r-390 at mailman.qth.net>
> Sent: Wednesday, October 04, 2006 9:41 PM
> Subject: [R-390] Digital readout
>
>
>> A digital readout mod actually did exist. It was an add-on using 
>> seven segment leds, stealing its power from the power supply. I was 
>> in Japan and noticed a few of these mods used on R-390A's for an 
>> intercept mode other than Morse code. Pretty cool, no calibrating was 
>> required and they read down to 100 cycles. I was lucky enough to talk 
>> the maintainance NCO out of one. The BFO did not change the frequency 
>> readout. Of course, in those day, I didn't realize what I had and it 
>> is long gone. I have never seen another one. Rich.
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>
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