[Elecraft] Synthesizer Issue

[Edward R Cole]

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 <gm4jjj at yahoo.co.uk>
To: Wayne Burdick <n6kr at elecraft.com>
Cc: elecraft <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] Synthesizer Issue
Message-ID: <E456211E-DC8B-4EA5-9FB2-C5C4DEBF095A at yahoo.co.uk>
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 <n6kr at elecraft.com> 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:
     dubususa at gmail.com