Coincidentally I just got one of these nifty little dongles this week. A Nooelec R820T USB SDR. Not expecting much, I'm definitely very pleasantly surprised. Mine's good down to about 25 MHz and is really best for FM at VHF and higher frequencies. That said, it does a decent job on SSB and happens to juuust have the range on the downside to monitor my 160m-10m HF rigs' signals. The supplied antenna is not very good but happens to work perfectly as an attenuated signal source for the dongle when using as a poor-man's spectrum analyzer.
I figured out how to narrow down the bandwidth and use it as a spectrum analyzer down in the 28MHz region with my HF radios to check out the transmitted signal of my radios. It gives a really useful spectrum analyzer-type readout via SDRSharp (what I'm using instead of HDSDR). I checked the carrier set points/filter skirts on several of my radios and was surprised to find a couple of them were off quite a bit. My TS-450 has a wider filter installed (2.7KHz vs the stock 2.4). I thought I had the filter skirts in the right place, but on the "dongle-scope" I could immediately see that there was some signal over on the unwanted sideband. I brought it back until I had a nice full signal placed right where I wanted it on the one sideband! Guys I talk to regularly said they could tell a difference right away and the radio sounds fantastic. Less muffled, clearer, and more punch without sacrificing the nice lows. Looking at the frequency response on the screen, I knew exactly why it sounded better.
Same story on my TS-850. I got those filter skirts right where I wanted them and got rid of a bassy-mushy sound and got an extra 200-300Hz on the high side. I could also see right away what the "high boost" button did for my audio. Running pink noise through the mic, the high boost brought the mids and highs up to make the audio flat across the board.
Next was checking out my Icom IC-7000 and the different transmit filter widths. Hole cow, those are some sharp skits on transmit, with the high and low cutoffs exactly where I set them to be! Really amazing what this $20 gizmo can do. For me, it's like having a $1,000 spectrum analyzer letting me *finally* see exactly what my transmitted signal looks like. Can't wait to see what software will be written for these in the future, as the possibilities are practically endless.
