[R-390] 200KC calibration crystal source

[Francesco Ledda]

The temperature at which the Freq/Temp ratio is minimum is called the
Crystal Turning Point.

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of Cecil Acuff
Sent: Friday, March 30, 2007 6:55 AM
To: Phil M.; Bob Camp
Cc: r-390 at mailman.qth.net
Subject: Re: [R-390] 200KC calibration crystal source


If I'm not mistaken the crystal oven for the 17Mhz crystal and the 200KC
crystal are not ovens that are turned off by the switch on the rear.  The
difference between these crystals and those in other radio's that don't use
ovens is in the design of the crystal.  The crystals in the 390A were
designed to be operated at an elevated/controlled temperature to perform
properly....the ones in other radio's were designed to perform properly at
ambient....operate either outside those parameters and the
frequency/stability changes dramatically.  A look at the stability -vs- temp
curves for the two types would reveal this quite clearly.  (I'm sure there
is some technical name for those curves...just don't know it)   I do know
that ovenized crystals have a long flat plateau in their curve that once up
to temp allows a fairly wide (relative) window of temperature variance with
little resulting frequency change.  Below that temp. you fall over a knee in
the curve and it's down hill pretty much for a long way.

Just some thoughts...

Cecil...




----- Original Message -----
From: "Phil M." <pmills7 at houston.rr.com>
To: "Bob Camp" <ham at cq.nu>
Cc: <r-390 at mailman.qth.net>
Sent: Friday, March 30, 2007 4:43 AM
Subject: Re: [R-390] 200KC calibration crystal source


>
>>
>> Taking the 17 MHz crystal out of the oven is not going to help the
>> stability of the radio much at all.
>>
>
> I don't think it will hurt the stability of the radio much at all either
> for
> typical swl and amateur.  It is used only on the bands up
> to 8 mc.  Many other fine receivers are quite stable with none of their
> xtals in ovens.  Many of us use our  R-390A's with the ovens turned
> off anyway.
>
> thnks, Phil
>
>
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