George,
This is really great news. I'll post it on the Ten Tec Reflector-- put me
down as one wanting an Omni VI CW roofing filter with 500 Hz offset (and 600
Hz BW).
Are there nine others out there in Ten Tec land who want
a CW roofing filter that will match up withe the Ten Tec 221 IF filter ?
Let George know.
73,
Chuck NI0C
----- Original Message -----
From: "International Radio" <inrad@rosenet.net>
To: "Chuck Guenther" <ni0c@earthlink.net>
Sent: Sunday, January 16, 2005 12:30 PM
Subject: Re: [TenTec] INRAD Omni VI roofing filter kit - success
> Chuck,
>
> I can get other filters with any offset we want. We need a minimum order
of
> 10 pcs to do this.
>
> George
>
>
>
> ----- Original Message -----
> From: "Chuck Guenther" <ni0c@earthlink.net>
> To: <tentec@contesting.com>
> Cc: "International Radio" <inrad@rosenet.net>
> Sent: Saturday, January 15, 2005 12:32 PM
> Subject: [TenTec] INRAD Omni VI roofing filter kit - success
>
>
> W4ZV quoted George at Inrad as follows: "Note also that a 4
> pole, 600 Hz filter centered on 9000.7 will pass just about all of the
> energy getting through your special 250 Hz filter."
>
>
> This is true; however if you set the radio for a 500 Hz sidetone (and
> offset), you will get a frequency response that is asymmetrical (skewed
> towards the high side) due to the mismatch in center frequencies of the
> filters. In order to center your listening frequency in the passband of
the
> cascaded combination, you will have to increase your offset frequency (by
> adjusting the sidetone in the radio). I used the nominal filter cutoff
> frequencies and bandwidths to calculate an "optimum" offset frequency of
544
> Hertz for the 600 Hz roofing filter and the Ten Tec 221 filter
combination.
>
> Here's how I did the calculations:
>
> Roofing Filter 600 Hz BW centered at 700 Hz Nominal cutoff
frequencies
> (-6 dB) are 462 and 1062 Hz
>
> Ten Tec 221 Filter 250 Hz BW centered at 500 Hz Nominal cutoff
> frequencies are 390 and 640 Hz
>
> For the combo: the lower cutoff is approx. 462 Hz and the upper cutoff
> is approx. 640 Hz , resulting in a bandwidth of 178 Hz and a
(geometric
> mean) center frequency of 544 Hz.
>
>
> A similar analysis substituting the Inrad 753 for the Ten Tec 221 gives a
> center frequency of 620 Hz and a bandwidth of 370 Hz in combination with
the
> CW roofing filter.
>
>
> I was interested in the latter combo, because that's what I'm currently
> using in my radio. I've been using a CW offset of 550 Hz (which appears
to
> be 70 Hz lower than optimum), and have noticed the asymetrical response
> skewed toward the higher frequencies in my operations. Of course this can
> be compensated to a large extent by adjusting the passband tuning in the
6.3
> MHz IF.
>
> 73
> Chuck NI0C
>
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