[Elecraft] SDR-IF and I/Q questions

[Larry Phipps]

Dick, if some programs work, then your levels may be low. PowerSDR/IF 
and NaP3 use an algorithm developed by Flex Radio called WBIR (Wide Band 
Image Rejection). It does a phenomenal job of eliminating images (>80dB) 
but is sensitive to levels, requiring a minimum amount of total signal 
power in the display to work. Since you say that other programs work, 
your issue may be levels. Most SDR users have no trouble with this, but 
there are stubborn cases like yours that pop up. They are usually 
related to sound card drivers or other system settings... or even bad 
cables. I had one customer who sent me his whole setup, and I found that 
his new cables from Radio Shack had about 10 ohms resistance between 
center pin and shield. There are tens of thousands of SDR users out 
there who are successfully using them, so these things can be solved. 
Pete and I have been talking about an indicator for NaP3 that would 
graphically display the overall balance of the sound card channels as a 
way to verify that the channels are matched within the range necessary 
for WBIR to work, but this would take some thought... and work. It would 
be worthwhile, though, for the percentage of users with stubborn image 
issues.

One very simple program, that provides all the features of the P3 except 
"fixed tune" mode, is TRX-Pan. It is extremely well integrated with the 
K3, and has a very simple manual image rejection adjustment (sliders for 
gain and phase). You set it once and forget it. There is no automatic 
"learning" needed and it will not change with levels or time. The 
tradeoff is that image rejection across the display will vary from about 
60-80dB. Only the very strongest signal (S9+30dB or more) would produce 
an image, and it would be 60-80dB weaker than the signal. Since the 
adjustment is manual, you can easily tell if your sound card has a 
problem, and make external adjustments while watching the image for 
changes. TRX-Pan requires LP-Bridge or TRX-Manager as the link between 
the rig and software. It is very easy to set up, especially with 
LP-Bridge. Everything you need can be found here...

http://www.telepostinc.com/TRXP.html

73,
Larry N8LP



On 11/15/2011 3:53 AM, elecraft-request at mailman.qth.net wrote:
> Date: Mon, 14 Nov 2011 12:42:41 -0600
> From: "Richard Fjeld"<rpfjeld at embarqmail.com>
> Subject: [Elecraft]  SDR-IF and I/Q questions
> To: "elecraft posting"<elecraft at mailman.qth.net>
> Message-ID:<20779EE975F7478494FA31FC637B8D30 at BIOSTAR>
> Content-Type: text/plain;	charset="Windows-1252"
>
> Well Dave, maybe I am missing something here, but this thread has been
> about the anticipated KX3 and having a Pan-Adapter to use with it.  As I understand
> it, the I/Q leads are being brought out, but not the IF.  So other SDR receivers, or adapters, are not
> needed. Therefore, we are down to finding acceptable software, soundcards, and computers
> to make it work on a par with a P3.
>
> The programs I tried that are not producing mirrored images are lacking good control between radio and software. No 'search and pounce' capability, and time consuming to adjust as the frequency was changed beyond the display width.  Not hardly on a par with a P3. Perhaps there is something out there that I am not aware of. I'll concede that, but if it is a commercial product, I want to exercise 'buyer beware'.
>
> I find PSDR-IF would be a very good match if it wasn't for the mirrored images that fills a crowded
> screen. Thanks to a fine gentleman who sent me this link, it shows I am not the only one
> having this problem.  Go to:
> http://groups.google.com/group/powersdr-if-stage/search?group=powersdr-if-stage&q=image&qt_g=Search+this+group
>
>
> and click on the posts with "image" to see all the posts on this topic.  Many people are having trouble
> with it.  AND, it pretty well identifies the problem.  If it ever gets fixed, we will have something encouraging.  At the speed it is going, it may be only for younger people.
> 73,
> Dick, n0ce