[TenTec] CW filter for Omni-VI+.... What model? 250Hz, 9MHz... LOW TONE CW!??

[Mike Hyder --N4NT--]

I divided 250 Hz by 9 million Hz and got 0.00002778.  I suppose I must then 
move the decimal two places to the right, or 0.002778% to get the percentage 
of change needed to move a 9 MHz crystal 250 Hz.  I don't vouch for the math 
and can't get my head around numbers like that but am sure you can.  In my 
opinion, Ten-Tec would have to pay dearly for such accuracy in the crystals 
and might well move their frequency a quarter kHz with capacitors.

My statement was based upon something I heard from Ten-Tec or general lore 
and it was based on reality rather than theory.  As I dimly recall, I was 
discussing the filters and wishing I had the 500 Hz centered one.  The other 
fellow said that the only difference between them was the capacitors.  I 
should have asked further and taken notes, huh?  Perhaps we can get a 
willing soul to examine his 500 Hz centered filter and report the capacitor 
values so we can compare them to a 750 Hz centered filter.  Perhaps we can 
get a kind soul at Ten-Tec to give us the specifications for the filters. 
Either way might help us better understand what Ten-Tec did and why they did 
it.

Mike

----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at weather.net>
To: <tentec at contesting.com>
Sent: Friday, October 09, 2009 03:29 PM
Subject: Re: [TenTec] CW filter for Omni-VI+.... What model? 250Hz,9MHz... 
LOW TONE CW!??


> On Fri, 2009-10-09 at 15:14 -0400, Mike Hyder --N4NT-- wrote:
>> Somewhere along the line I got the notion that the difference between the
>> filters centered at 750 Hz and centered at 500 Hz was only the capacitors 
>> on
>> the filter board.
>>
>> Did I make this up or can anyone shed light on it?
>>
>> Mike N4NT
>>
> More properly its the frequency of the crystals that set the center
> frequency, the capacitors set the coupling between crystals, and the
> bandpass. Dragging the crystals with different capacitors might work but
> would change the filter terminal impedance that would probably cause
> increased insertion loss. 250 Hz shift on a 9 MHz filter wouldn't
> require a change in capacitors at all, just the crystals.
>
> 73, Jerry, K0CQ