As I see it, for normal rigs the SSB mode is convenient, but if you had a
rig with a BFO swing between 0 - 2 khz and position it around 1.5 Khz then
that would work in the CW position and have the advantages of narrow cw
filters.
Some of the old RA17 receivers had a BFO swing of 4 Khz to interface with
some external MODEMS that needed an offset of 3 Khz.
If you could find an amateur receiver that had a suitable bfo offset then
the CW position would work better.
Opera could probably be redesigned for an ofset of maybe 800 Hz and could
then be used in the normal way in CW RX mode
g3kev
----- Original Message -----
From: "Mike Dennison" <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Wednesday, July 11, 2012 9:18 AM
Subject: Re: LF: OPERA Question
> > Narrow IF filters are not desirable and reduce the
> > performance of the demodulator , better simply use SSB filter
> > GL ..73 -G..
>
> Graham,
>
> Why is that the case? What does the considerable extra bandwidth
> achieve? Is the SSB bandwidth optimal, or would it be even better
> with 10kHz bandwidth, or 100kHz?. Why is 3kHz better than perhaps
> 1kHz or 2kHz?
>
> At first glance it appears crazy to let in all sorts of adjacent
> channel QRM (the bandwidth is more than ten times the size of the
> entire Opera window) when using a mode that occupies a fraction of
> 1Hz.
>
> Is it simply that the 1.7kHz Tx tone is high enough for the SSB
> filter to kill its harmonics, and on receive it is difficult to get a
> 1.7kHz tone out of a CW filter, even with passband shifting.
>
> Am I missing something?
>
> 73 de Mike, G3XDV
> g3xdv.blogspot.co.uk
> ================
>
>
>
|
