It is my understanding that the displayed BW is that of the audio. At least
with my single 2.8KHz filter, there is a caveat: the operational bandwidth
can't exceed the i-f filter bandwidth, even though the display will lull you
into thinking so, if you're not careful.
With my radio if I normalize the BW, the Lo Cut defaults to 100 Hz and the Hi
Cut to 2.9KHz. If for some reason I adjust the Hi cut to a higher frequency,
the display will still show the Lo Cut at 100 Hz. If for example I decide to
widen the BW to 3.5 KHz (Hi = 3.6) to improve fidelity the Lo Cut readout
will still display 100 Hz, but the low frequency response isn't what it was
before.
In doing this with my radio, a 300 Hz tone is down 12 dB. This was because
changing the DSP limit moved the i-f filter pass-band with respect to the
signal. In other words, the DSP BW is *not* independent of the i-f filter BW.
Of course it can be argued that the readouts are displaying the audio pass-band
and this is to be expected. But I think this is wrong. Perhaps some of the
reports of lousy audio result from this mistake.
Wes Stewart, N7WS
--- On Wed, 4/8/09, Don Wilhelm w3...@embarqmail.com wrote:
From: Don Wilhelm w3...@embarqmail.com
Subject: Re: [Elecraft] AM RX bandwith
To: Jan Erik Holm sm2...@telia.com
Cc: Elecraft Reflector elecraft@mailman.qth.net
Date: Wednesday, April 8, 2009, 8:37 AM
Jim,
The change is only in the displayed width. Before it was
the IF
bandwidth, and now it is the audio bandwidth - for AM, that
will be 1/2
of the IF bandwidth, so 10 kHz before equals 5 kHz
displayed now. It
is consistent with the other bandwidth displays that
indicate the audio
channel width.
73,
Don W3FPR
Jan Erik Holm wrote:
This might be a stupid question since I think this
has been on the list before.
Just upgraded from 2.76 to 3.06. I´m using 13 KHz
FM filter for AM RX´ing.
Before I could see 10 KHz DSP bandwith but now 5.00
KHz.
Something has changed. What bandwith do I get? Did
I get 10 KHz before and now it is changed to 5 KHz or
is it just one sideband I´m seeing? I´m
just puzzled.
This is how I like to have it. Would like to be able
to
widen the DSP all the way out to the filter (13 KHz)
but it seems to me it´s not possible, maybe it never
was.
Sorry if this has been on the agenda before.
73 Jim SM2EKM
PS: When I think about it maybe I saw 9 KHz before and
not 10, well one or the other.
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