Gee, I defer to you experts. It is quite possible that you are wrong but
we'll never know, will we?
Maybe we could move the carrier oscillator 250 Hz?
----- Original Message -----
From: <d.e.warnick@comcast.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Saturday, October 10, 2009 08:32 AM
Subject: Re: [TenTec] CW filter for Omni-VI+.... What model? 250Hz,9MHz...
LOW TONE CW!??>
>
> Just knowing the value of the capacitors is not enough. That would assume
> that identical crystals were used in both the high-tone and the low-tone
> filters. We cannot make that assumption. Therefore, the individual
> comparing the filters would have to measure the crystals used for center
> frequency at least. At that point, if the crystals were identical, we
> could continue the process of measuring the capacitors necessary to pull
> their center frequency. As Jerry's e-mail stated, that is not the purpose
> of the capacitors in this filter design.
>
> Dave
>
> WA3MKB
>
> ----- Original Message -----
> From: "Mike Hyder --N4NT--" <Mike_N4NT@embarqmail.com>
> To: geraldj@weather.net, "Discussion of Ten-Tec Equipment"
> <tentec@contesting.com>
> Sent: Saturday, October 10, 2009 7:32:20 AM GMT -05:00 US/Canada Eastern
> Subject: Re: [TenTec] CW filter for Omni-VI+.... What model? 250Hz,
> 9MHz... LOW TONE CW!??
>
> 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@weather.net>
> To: <tentec@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
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