A Second SDR for the Desktop – 2


Posted 11/24/2015:

So, today I had my first partial CW QSO, using the Soft66 Lite SDR. I used the Omni for the TX, and the Soft66 for the RX, on 40 meters. This was at high noon, when the band was really out, and all we managed to do was to exchange reports (559 each way before the band evaporated). I couldn’t pull him in with the Omni RX, either, after I switched to it as a last resort. Hopefully we can make a better contact at another time (with with W8BJO).

A couple hours later, I managed to snag N4IVE on 40 meters, using the Soft66 as the RX, and again the Omni as the TX. I was able to copy about 95% of his side of the QSO, in spite of the fact he was only running 5 watts. At the very end of the QSO, I turned the volume up on the Omni, and I found that his signal was better on it. I guess we’ve work to do, to figure out a way to put the two receivers on par with one another. Might be dreaming there :-). Still, it was interesting. I was able to use the Linrad software to effect a very narrow filter, making his signal stand alone in the quiet. Occasionally, he’d dip out, but all in all it was not a difficult contact.

As the evening rolled on, the normally strong 40 meter evening CW signals rose up out of the noise, and as they did so, the perception of differences in reception between the Omni and the little SDR kit seemed less noticable. At 2115 GMT, K2HYD answered my CQ. The ensuing QSO was conducted only via the SDR radio receiver, and was very pleasant. About two thirds of the way through the QSO, a big close-by signal threatened to end it, but the filtering capability of Linrad saved the day. We exchanged 589 reports, even though we were both using very limited antennas (random wire for him, and attic dipole for me).

Tonight the S meter on the Omni is sitting someplace between S3 and S4, for the noise. Signals that barely nudge the S meter above that noise level, or do not bump it at all, can be heard in the Omni’s speaker. The signals that do not bump the Omni’s S-meter, are not showing in the waterfall display of the SDR setup. Right now, the Omni is the DX machine. But, I didn’t really expect a DX machine from the 2-dinner value SDR, either. Everything’s relative. There was one signal, making just the slightest trace across the SDR waterfall, while on the Omni it was making a barely perceptible nudge of the meter. I could copy nothing on the SDR, no matter how I tweaked Linrad, but could copy 25% to 50% of that CW signal on the Omni. Hair splitting, unless you’re a DX hound.

A very light, but well defined trace on the Linrad SDR screen was heard without straining (100% copy) by listening to it with headphones plugged into the SDR. This CW signal was somewhat more comfortably heard on the Omni, where it was bumping the Omni’s S-meter one full S unit above the noise (about S4.5 or S5). The thing is, most of my rag-chew QSOs deal with signals that are more than one S unit above the noise. S5 or S7 signals are more common, and for those QSOs on an uncrowded band, there’s not much difference between the two radios. It reminds me of people who are looking for 2 db noise figures on HF, where the floor is ALWAYs much higher. DX hounds put a high weight on all those signals between the noise and a half tick-width above it. But that’s not my usage pattern.

When it comes to spurs and image rejection, there’s a different story to tell. Of course the Omni shines there, but I’ve yet to quantify the miniature SDR radio in this regard. While it’s not anything like the Omni, Linrad can do a surprising mediation of some of the difference, IMO.

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The radio I’ve purchased and built, and am referencing in this post, is available from the following site:


This author and site (amateurmiscellany) has no affiliation with the Soft66 or its website.