Dave, Wayne, others:
Improved synthesizer phase noise will improve eme similarly to any
weak-signal reception in presence of strong adjacent frequency interference.
Dual polarity diversity reception for eme requires software to
recover the polarity information. Two programs that I am aware of do
this: SM5BSZ's Linrad (Leif Asbrink) and MAP65 (Joe Tayor).
The software require two phase-locked receivers tuned to the same
frequency to produce two IQ outputs which are in-phase with each
other. Then the amplitude difference will produce polarity
information which can be displayed and the software can digitally
maximize SNR for best sensitivity (digitally aligns the output to the
polarity of the signal).
This does require both preamps, downconverters, receivers, and SDR's
to have a constant phase relationship. Both sw have calibration
routines to compensate the fixed phase difference in signal
paths. Gains need to be balanced, as well.
This is virtually impossible to achieve perfectly so the sw designers
added a utiltity to test the difference and add digital compensation
to remove this. My preamps are within less than a dB difference in
gain and the downconverter uses an identical ckt as does the
K3/KRX3. I use two LP-Pan for the SDR running on the 1st IF's of the
K3/KRX3 with them using a common LO. Finding a test signal to
perform the calibration is the hard part. Some eme signals are close
to 45-degree polarity that is needed for this procedure.
I will eventually upgrade my K3 with the new synth boards.
73, Ed - KL7UW
Date: Tue, 3 Mar 2015 22:21:13 +0000
From: David Anderson <[email protected]>
To: Wayne Burdick <[email protected]>
Cc: elecraft <[email protected]>
Subject: Re: [Elecraft] Synthesizer Issue
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Wayne,
For folks that were using the two receivers for VHF EME polarity
diversity reception over a wide bandwidth with MAP65 software, where
they would have gain and phase matched preamps this must be an
improvement for them.
I think it was not generally understood that the absolute value of
the phase relationship of the receivers would change as the VFO was
moved. The only person I know that is currently using his K3 for
doing this is Ed KL7UW, so he may be interested in this.
73
David Anderson GM4JJJ
> On 3 Mar 2015, at 02:21, Wayne Burdick <[email protected]> wrote:
>
> Some users of the new synthesizer have also reported an
improvement in the way diversity mode sounds. This is due to a change
in the way the receivers are driven by the synths.
>
> In diversity mode, as long as the main and sub crystal filter
offsets are matched, both receivers are driven by the main synth (the
sub synth is not used in this case). So, when the VFO is moved, the
local oscillator phase relationship remains stable between the main
and sub receivers.
>
> With the original synths, moving the VFO even a small amount
causes both the main and sub synths to be updated. Since they use
separate LC oscillators, the phase relationship will change. The two
will remain phase-locked to the reference, but the absolute value of
the phase between the two synths will be some value between 0 and 180 degrees.
>
> We'll add this to the FAQ.
>
> 73,
> Wayne
> N6KR
73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[email protected]
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