EMRFD Message Archive 1163
Message Date From Subject 1163 2007-11-13 01:01:27 Ed Almos Frequency Offset in Phasing Transceivers I need some help. Hopefully Rick Campbell KK7B monitors this board but
if he doesn't please could someone show him this message?
When using a homebrew transceiver based on a BFO and filter(s) it's
easy to work out where you need to tune to work a station. You alter
the VFO until the voice sounds about right then you give them a call,
the BFO which is offset from the carrier does all the math.
What happens if your rig uses phasing for SSB/CW reception, such as
those featured in EMRFD?
Let's use CW as an example. I tune around and find a station calling
CQ. With my rig in USB mode I alter the VFO until I get a pitch which
sounds comfortable, in my case about 700 Hz. Looking at the rig I see
that the frequency display reads 14.005. Should I then transmit on
140043, 14.005 or 14.0057 so that he can hear me?
Edward Almos HA6SST
1164 2007-11-13 06:08:35 Bill Noyce Re: Frequency Offset in Phasing Transceivers On 11/13/07, Ed Almos <email@example.com> wrote:
>I'll assume that the frequency display shows the actual frequency of
> Let's use CW as an example. I tune around and find a station calling
> CQ. With my rig in USB mode I alter the VFO until I get a pitch which
> sounds comfortable, in my case about 700 Hz. Looking at the rig I see
> that the frequency display reads 14.005. Should I then transmit on
> 140043, 14.005 or 14.0057 so that he can hear me?
the receiver's oscillator...
If you hear a 700 Hz tone in USB mode when your carrier oscillator is
at 14.005, then you know he's sending on 14.0057 MHz. You want to
arrange to transmit on that same frequency. One way is to run a
simple CW oscillator at 14.0057 using the same kinds of VFO-offset
circuit as the simple direct-conversion transceivers. (This works for
CW, but not SSB.) Another approach is to push a 700 Hz tone through a
phasing exciter set for USB, with the oscillator at 14.005 -- just
mirroring what's happening in the receiver. (This latter approach is
how you would do it for SSB -- using microphone signals rather than
the 700 Hz tone.)
If your rig's frequency display doesn't show the actual VFO frequency,
but rather tries to compute the frequency of a received CW signal,
things get more complicated. In this case, if the preferred audio
tone is 700 Hz, the frequency display (in USB mode) would show VFO +
700 Hz. So we can assume the CW signal was transmitted on 14.005, and
the VFO is set to 14.0043 MHz. The two choices then become: Send CW
at 14.005, or Send a 700 Hz tone at 14.0043 USB. As before, the
former requires an offset circuit, while the latter keeps the transmit
VFO frequency the same as the receive VFO frequency.
Hope this makes it clearer,
-- Bill, AB1AV
1175 2007-11-21 07:07:56 cwfingertalker Re: Frequency Offset in Phasing Transceivers Edward,
Try looking at the r2pro Yahoo group for an answer to your questions. That group is
all about Rick's Phasing designs.
Bill Martin N7EU
Sam's Valley Oregon.