[TenTec] Receivability

[Steve Ellington]

Another Pro bites the dust. Thanks for that bit of techno info.

Steve
N4LQ

----- Original Message -----
From: "WA3FIY" <wa3fiy@radioadv.com>
To: "George, W5YR" <w5yr@att.net>
Cc: <tentec@contesting.com>
Sent: Tuesday, October 29, 2002 1:40 AM
Subject: Re: [TenTec] Receivability


> On 28 Oct 2002 at 14:10, George, W5YR wrote:
>
> >
> > Where this all falls apart is when an op wants to copy a low beatnote
> > and yet use a fairly wide filter. I once had a fellow complain that
> > his new Icom 756PRO was defective because when set for a 450 Hz offset
> > and 800 Hz bandwidth, he could hear QRM from "the other side." No
> > amount of explanation could convince him that such a setup was doomed
> > from the start . . .
> >
> I'm not sure I understand your statement that this setup was doomed
> from the start.  Perhaps it was for the 'PRO, although I thought they
> used the phasing method of sideband selection and generation.
>
> My Pegasus uses the "Weaver Method" which is a type of phasing
> method and is quite capable of setting the CW offset at 450 hz and
> bandwidth at 800 hz or more without hearing anything on the other
> side of zero beat.   I just ran a test with a 20 over 9 carrier on a RX-
> 320, Pegasus and Argonaut V.  In each case I set the offset at around
> 400 hz and bandwidth at 1000 hz.  Also in each case, I heard a 20 over
> 9 signal on one side of zero beat and nothing on the other.  The reason
> for this is that the phasing method does not depend on the skirts of
> the filter to reject signals on the opposite side of zero beat.  It uses
> the phase relationship between two phases of the signal and two phases
> of the BFO, each shifted 90 degrees.  When phasing was done with
> discrete components, component tolerance and limitations on circuit
> designs limited the suppression of the opposite sideband to something
> around the 40 db range over a typical 2 to 3 khz bandwidth.  Since DSP
> is a math process, the tolerances of individual components goes away
> and one has a near perfect single sideband detector or generator.
>
> BTW, just for the fun of it, I took the bandwidth to 3 khz on the
> Pegasus with a 400 hz CW offset and could hear the desired signal over
> the entire 3 khz bandwidth and again nothing on the other side!
>
> -73-
>
> -Lee-
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