Using the V6.2 lite Softrock Rx as a panadaptor with Elecraft K3

[Jerry Flanders]

I posted this a week ago, but I am posting it again because kb9yig
has decided to resume selling this $12 SR lite 6.2 kit for a limited
time. See [hidden email] or email Tony direct at  direct
at raparks @ ctcisp.com (remove spaces around "@").

Jerry W4UK

As a panadaptor for my Elecraft K3, I have one of KB9YIG's 6.2 lite
SR40 receivers with the special IF for the K3 (32764 KHz crystal).
This gives the SR40 a LO freq of 8191, 24 Khz below the 8215 IF of
the K3. I routinely watch a panorama of about +/- 24 Khz on the
PowerSDR display (using 96 KHz samping).

I also have one of Jack Smith's Z-10000U buffer amplifiers (Clifton
Laboratories) running between the K3's KXV3 output and the SR40 for
isolation. (I didn't test to see if the isolation is really needed -
maybe not, since the LO is offset 24 KHz.)

The above combination is giving me the best panadaptor I have ever
used, and I have been using them since Heathkit made one for the
Heathkit SB303 in the early '70's. The current ICOM receivers have
panadaptors, but the resolution is lacking. With KB9YIG's SR40
rx  and PowerSDR, I can even identify the various signal types on
sight. I am using the version of PowerSDR that has simultaneous
waterfall and panorama.

I have PowerSDR calibrated so that the display gives an S9 reading
when the K3 sees a 50uV S9 signal from my XG-2 generator. Sensitivity
is amazing - I can see signals on the waterfall well down into the noise level.

As an indication of what is possible software-wise with the
Panadaptor add-on, I am able to run PowerSDR and Skimmer (or Rocky,
just as well) simultaneously here on a Sempron 2 GHz 1GB machine,
along with Writelog with RTTYRITE in CW mode as well as CWGET all
simultaneously. PSDR and Skimmer are both using the same two input
channels of my Delta-44, and Skimmer sees the entire I/Q IF range,
not just the audio. No audio routing tricks or "Y cables" are needed.
The remainder are using the on-board VIA AC97 sound card. Total CPU
usage ranges 50 - 70% with all running or around 20-40% with PowerSDR
but without Skimmer/Rocky. The computer also generates CW and I have
not seen any CW keying hiccups so far in limited S&P recently in a
contest even at 70% CPU. This machine does not use on-board video,
which might slow it further - it has a dual-monitor AGP video card.

This is a simple panadaptor setup - I view only and have no K3
control or click tuning from PowerSDR or Rocky/Skimmer. (Update - I
have control and click tuning now using the WU2X version of PowerSDR.)

FYI, it is often possible to run multiple apps on the same sound card
- I once had 8-10 copies of MMTTY running on a VIA AC97 on-board
sound "card" under XP home as a test to see if multiple simultaneous
RTTY profiles worked. Each copy only added about 2% to the CPU load.

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[David Cutter]

Another SDR is advertised by Elektor

http://www.elektor.com/

GBP72 for the assembled and tested pcb.

David
G3UNA  

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[Geoffrey Mackenzie-Kennedy]

Jerry Flanders wrote on Tuesday, June 03, 2008 1:34 AM

> I also have one of Jack Smith's Z-10000U buffer amplifiers (Clifton
> Laboratories) running between the K3's KXV3 output and the SR40 for
> isolation. (I didn't test to see if the isolation is really needed - maybe
> not, since the LO is offset 24 KHz.)

--------------------------------------------------------------------

Jerry, in my opinion it is always wise to use a buffer amplifier which
exhibits a high degree of reverse isolation, such as Jack's Z-10000, when
picking off a sample of signals from a receiver's signal path. As I am not
too familiar with the K3 I could be wrong but I believe that the point at
which you are taking a sample for the SR40 is somewhere between the first
mixer and the input of the 8.215 MHz IF filter. If that is the case and you
did *not* use a suitable buffer amp, the SR40's LO 'leaked' signal would
most likely appear at the input of the filter even though its offset is 24
kHz. This means that the filter has to deal with more unwanted signal power
than just the 'routine' stuff coming from the mixer. Even worse is the
possibilty that the SR40's LO 'leaked' signal might back up into the mixer,
mix with the LO or its harmonics and/ or other signals in the mixer, and
produce its own family of  spurious products which would cause additional
problems for the filter. Some of these products might even lie within the
filter's passband and be heard, but I have not done the maths to find out if
that is the case.

As an aside, a crystal filter can itself generate significant IMD products
if overdriven, which is why it it is essential to measure the IIP3 of a
crystal filter at various input levels and spacings when designing a
receiver.

73,
Geoff
GM4ESD

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