[R-1051] Frequency standard module

[Bob Camp]

Hi,

There are several generations of frequency standards out there for the
R-1051. More or less:

1) Early production parts with BT cut crystals in them - properly made.

2) Early production parts with AT cut crystals in them - properly made.

3) Later production and replacement parts with who knows with in them - made
by the "paint by numbers" approach.

So what does this all mean in plain simple English:

A BT cut crystal has a parabolic temperature coefficient and it peaks at the
operating temperature. An AT cut crystal is a third order curve and it hits
a local minimum at the operating temperature. If you turn on your cold radio
and the frequency goes up as it warms up you have a BT cut crystal. If it
goes down in frequency you have an AT cut crystal. More or less forget about
replacing BT cut crystals ....

A properly made frequency standard should have the oven set to match the
individual crystal used to build it. This isn't to hard to do. You simply
move the temperature and watch for a minimum frequency if it's an AT or a
maximum if it's a BT. A frequency counter that will read out to 0.01 Hz is a
nice thing to use when you do this. Once the oven is set to this point it's
temperature stability *should* be as good as it's going to get. This should
minimize post warm up drift. Most radios that take a *long* time to warm up
have ovens that are off temperature.

If you have one of the weird late production or replacement oscillators then
it may never have been set to temperature ever. It also may or may not set
properly when you try to adjust it. There's along story about the source of
these parts, but this post is already a bit to long anyway ...

Since the inside of the oven is the hottest part of the radio it's not to
surprising that parts in there fail from time to time. You may fix one
problem only to cause another. Probably your best bet on a dead oscillator
is to simply find another one.

    Enjoy!

        Bob Camp
        KB8TQ



----- Original Message ----- 
From: <jan at skirrow.org>
To: <r-1051 at mailman.qth.net>; <r-1051 at mailman.qth.net>
Sent: Sunday, May 11, 2003 7:53 PM
Subject: Re: [R-1051] Frequency standard module


> At 11:25 AM 5/11/03, James A. (Andy) Moorer wrote:
> >If someone sends me a copy, I'll scan it and put it on the web site.
Sounds
> >like a good thing to make available.
>
> I'm curious ... what is the problem people are having with this module?
>
> I ask, because I have six freq std modules - in three versions, and only
> two are what I would call serviceable. One or two 'sort of' work. They
> oscillate, but way off the correct frequency, but then will usually pop in
> after they warm up a bit. The others are dead - and the problem seems to
be
> the crystal. These are an unusual cut, I don't know what the electrical
> specs are, and I don't know if they can be rehabilitated.
>
> I have spent some time on the problem, but haven't been able to find any
> explanation, other than bum crystal. I've got on my (endless!) list of
> things to do to rebuild the circuit with a modern crystal style - has
> anyone tried this?
>
> If anyone has a fix, I'd sure like to know!
>
> Jan Skirrow, VE7DJX
>
>
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