[R-390] 200KC calibration crystal source

[Cecil Acuff]

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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