[TenTec] Omni VI Plus audio

[Bob McGraw - K4TAX]

The CW filter in the Collins 75S-3 on my desk has clearly and noticeably 
more ringing than either the 500 Hz or 300 Hz filters installed in my Omni 
VII.

73
Bob, K4TAX


----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at storm.weather.net>
To: <tentec at contesting.com>
Sent: Wednesday, March 19, 2008 10:32 PM
Subject: Re: [TenTec] Omni VI Plus audio


> On Tue, 2008-03-18 at 18:31 -0500, Bob McGraw - K4TAX wrote:
>> I suspect that you may have a defective filter.  The fact that you had to
>> pad an oscillator is a clue.  Or maybe a BFO crystal is out of tolerance.
>>
>> I measured the audio frequency response of my Omni VI Plus using the
>> sinewave/power method.  Once I did this, I was able to see the shape of 
>> the
>> filter and take into account the group delay which affects the "sound" of
>> the radio. I didn't do a squarewave response however.   I also confirmed
>> that the DSP artifacts were present in the RX signal regardless of the NR 
>> or
>> Auto Notch usage.
>>
>> I've found that the mechanical Collins filters used in the Omni VII offer 
>> an
>> significantly enhanced signal on SSB both in transmit and receive.  They 
>> are
>> clearly different than crystal filters regardless if they are ladder of
>> lattice configuration.
>>
>> 73
>> Bob K4TAX
>>
>>
> Ladder filters inherently have different upper and lower skirt slopes.
> They also inherently have a more rounded transition from pass band to
> stop band which gives them a much better time response.
>
> The Collins mechanical filter has enough design versatility to allow
> symmetry even when neither a ladder or a lattice filter, though the S-
> line vintage filters were really bad at ringing. I'm not noticing that
> so much with the modern Collins CW filter in my FT-857D.
>
> 73, Jerry, K0CQ
>
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