The standard 20 kHz roofing filter would work fairly well if incorporated
with a 12 kHz DSP filter.
Ron Castro
Chief Technical Officer
Results Radio, LLC
N6IE
www.N6IE.com
(Formerly N6AHA)
----- Original Message -----
From: "Kimberly Elmore" <cw_de_n5op@sbcglobal.net>
To: <tentec@contesting.com>
Sent: Wednesday, January 24, 2007 8:43 AM
Subject: Re: [TenTec] AM Receiver distortion in Orion II
>I haven't worked any AM yet with my O II, but I've listened a fair bit.
>I've not heard any of the distortion spoken of so far. But I'm certain that
>the 6 kHz bandwidth limit imposed by th eroofing filter severely affects
>the audio quality. There are no frequency components above 3 kHz hen using
>AM. Yet, if I listen to the same signal in SSB with the BW set to 6 kHz, AM
>sounds better than I've ever heard it. It seems that what we need for AM is
>a 12 kHz bandwidth roofing filter and 12 kHz DSP bandwidth.
>
> Kim Elmore, N5OP
>
> ----- Original Message ----
> From: Ron Castro <ronc@sonic.net>
> To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
> Sent: Wednesday, January 24, 2007 10:31:30 AM
> Subject: Re: [TenTec] AM Receiver distortion in Orion II
>
> The interesting thing about all of this is that on the Orion II AM
> stations
> sound substantially better in SSB (same 3 kHz audio BW) than they do in
> AM!
> I still think there is a DSP problem in the AM detector algorithm.
>
> Ron N6IE
> www.N6IE.com
> (Formerly N6AHA)
>
> ----- Original Message -----
> From: "Paul Christensen" <w9ac@arrl.net>
> To: "Carl Moreschi" <n4py@arrl.net>; "Discussion of Ten-Tec Equipment"
> <tentec@contesting.com>
> Sent: Wednesday, January 24, 2007 3:49 AM
> Subject: Re: [TenTec] AM Receiver distortion in Orion II
>
>
>>> Number 2, There is clearly a difference between the two recordings, so
>>> maybe
>>> someone in Tennessee has a tin ear?
>>
>> I just ran the two audio clips through SpectraPlus FFT software. The
>> .MP3
>> output is read directly by SpectraPlus internal to the sound card with no
>> audio cabling necessary.
>>
>> The O2 has a sharp AM audio response cutoff at exactly 3 kHz (6 kHz of
>> BW),
>> as expected. On the FFT display, it is clearly a very sharp DSP cut-off
>> with no detectable skirt. Audio response cuts off at 3 kHz and nothing
>> escapes beyond that point. The O2 low-end response extends to below 80
>> Hz,
>> but rolls off smoothly below 90 Hz.
>>
>> On the TS-870, the AM response is also quite sharp, but cuts off at
>> approximately 3.7 kHz. What we are all hearing is the significance of
>> the
>> speech intelligibility in the area between 3 and 4 kHz. That region does
>> more to add speech intelligibility than any other area of the audible
>> spectrum. This should come as no surprise when one looks at the
>> Fletcher-Munson family of loudness curves. At approximately 3.5 kHz, the
>> ear is most sensitive to absolute sound pressure level. Why? Because
>> the
>> ear canal terminates into the tympanic membrane and forms a closed
>> acoustical pipe whose average resonant frequency is -- about 3.5 kHz.
>> The
>> exact point of resonance is a function of the length and diameter of our
>> individual ear canals. So, a mere 700 Hz of added bandwidth makes a
>> significant difference in intelligibility and is one reason why ESSB
>> proponents have been advocating the use of extended-bandwidth SSB when
>> conditions permit.
>>
>> Although things start sounding even better beyond 4 kHz, diminishing
>> returns
>> sets in quickly. In the interest of allowing operators the use of
>> maximum
>> speech intelligibility versus spectrum conservation, 4 kHz for SSB and 8
>> kHz
>> for AM is an excellent choice for maximum occupied bandwidth when
>> operating
>> conditions allow it.
>>
>> Paul, W9AC
>>
>> _______________________________________________
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>>
>>
>
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