Allen, Carl is correct.
You don't need really steep skirts and deep attenuation with the roofing
filter.
The roofing filter's job is to add just enough selectivity to prevent
overloading of the down-stream circuits. The DSP filters on their own do
the job of providing the main selectivity and they do it quite well - far
better than the XTAL filters we were previously using for this job; assuming
their circuitry is not overloaded
In the old designs, the roofing filter had to assist with the overall
selectivity because the single XTAL filter in the downstream IF did not have
steep enough skirts nor enough ultimate attenuation.
Although good XTAL filters measured in the lab can show attenuation of up to
100dB, when inserted into a radio their ultimate attenuation typically falls
off to just 80 dB, due to blow-by. Cascading XTAL filters (i.e., roofing +
IF) raises the ultimate attenuation to about 100 dB.
When the Orion came out, I discussed this with Jack Burchfield and he
assured me that adding more XTALS to the roofing filter did not bring any
additional benefit. It just brings additional size, cost, attenuation and
points of possible failure.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of A R
Sent: Saturday, October 10, 2015 6:26 AM
To: n4py3@earthlink.net; Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] SSB and CW filters wanted
Carl,
Is that really true? Aren't the 218 and 219 employed as roofing filters in
the 1st IF, and isn't the DSP BW control in the 3rd IF? If strong adjacent
(and/or dirty) signal conditions warrant tighter/narrower BW roofing filters
than the narrowest 2.4KHz and 1.0KHz roofing filters supplied as "standard"
in the ORION, then wouldn't the option roofing filters at the 1st IF be more
effective in dealing with the consequences of strong adjacent/dirty signal
conditions than at the 3rd IF?
Allen--W7GIF
----- Original Message -----
From: Carl Moreschi<mailto:n4py3@earthlink.net>
To: Discussion of Ten-Tec Equipment<mailto:tentec@contesting.com>
Sent: Friday, October 09, 2015 7:33 PM
Subject: Re: [TenTec] SSB and CW filters wanted
You don't need them. The skirts on the Orion DSP filters are very sharp
making those filters not really needed.
Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com<http://www.n4py.com/>
On 10/9/2015 9:14 PM, Tim Wininger wrote:
> Looking for # 218 (1.8Khz) and #219 (250Hz) filters for a newly
> acquired Orion.
>
> Anyone got these filter excess to their needs?
>
> Thanks for the response,
>
> Tim, AB4B
> Rogersville,AL
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> sting.com/mailman/listinfo/tentec>
>
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