[R-390] Frequency meter

[Bob Camp]

Hi

As the other posts have mentioned it's not a simple thing.

A lot depends on how accurate you want to get. RTTY and SSB are the two 
things that most people would like to tune accurately. With AM the 
bandwidth of the filters makes a 10 or 100 cycle error a lot less 
important.

If you are going to tool up to do a full readout for SSB or you would 
need to measure:

1) The first crystal oscillator
2) The second crystal oscillator
3) The VFO
4) The PTO

The digital stuff to do that isn't terribly expensive these days, but 
it does make noise.

Once you had all the frequencies measured then oddly enough you would 
have to know what band you are set to. It turns out that several of the 
crystals are used for more than one band so there is no direct and 
simple way to guess the band in every case.

That all sounds like a lot of work and I'm lazy. If I was going to do 
it I'd fake it:

No matter what you need some way to track the band switch. Say we slave 
a pot to the shaft and measure the resistance.

The 17 MHz ovenized crystal isn't going to drift much I would simply 
measure it's frequency with a bench counter and store the result 
somewhere.

The same thing is true to a lesser extent for the crystals in the 
crystal deck. They do drift but maybe by sixty cycles. I would just 
measure them and store their frequency as well.

That gets us to the BFO and the PTO.

There is an old military mod that puts a multi turn gear drive and 
readout on the BFO shaft. The net result is the ability to reset the 
BFO very accurately. If you can lock down the BFO shaft fairly well 
(maybe mechanical detents) you can get around reading the BFO.

All that's left is the PTO. You can either count it's frequency or try 
the slave a pot to the shaft trick.

The cute thing about doing it al with pots would be that you have no RF 
counters at all. You are dependent on the radio not drifting but that's 
what the 390 is known for.

Definitely a bit far from the "well enough alone" zone thought ....

	Take Care!

		Bob Camp
		KB8TQ



On Sep 1, 2004, at 9:37 AM, Charles B wrote:

>
> Is there any place inside the R-390A where a frequency meter can 
> attached to get a frequency reading?
>
> Chuck
>
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