While several of the RTL and related dongles will do HF frequencies, you have to keep in mind the technical limitations beyond just the frequency coverage. Keep in mind this is not a slam on RTL dongles, they are a tremendous bang-for-buck. If you have realistic expectations, you don’t expect Corvette performance at a Chevette price, all is good. As it is the performance they yield is all out of proportion to the cost, they punch well above their weight class, but there are issues.
In the VHF/UHF range stations / channels are typically further apart than you find on HF. The limited dynamic range and poor image rejection of the 8 bit dongles is an issue, but not horrible. On HF things are more narrow and closer together, often with very strong signals (assuming a decent antenna) close to very weak signals, maybe even overlapping, a condition that is much less common on VHF/UHF.
The low cost RTL dongle will show their shortcomings much more often, and to a greater degree, on HF than they typically do on VHF/UHF. Images, saturation, clipping, etc. This happens whether you use direct sampling or an upconverter.
An SDR designed for HF operation will often be superior in several aspects over a wideband SDR used on HF. It may have band pass filtering or some other front end specifically designed for HF. Most of them are better resolution, not just 8 bit but more along the lines of 12, 14, 16, or more bits.
The results are that SDRs designed for HF are preferable if your target is HF. Unfortunately, such SDRs are typically more costly than some of the wideband, RTL based, SDRs.
AirSpy HF+, RSPdx, Elad FDM-S2, AFEDRI sdr, Kiwi SDR, Perseus SDR, various RFSpace SDRs, WinRadio G31/G33/G35DDC, etc. These are all very good performers, some of them world class, but starting at a price point of $200 on the low end and going up into the several thousand USD range. I currently use or have used all of these, and more, except the RSPdx, I have not tried that one yet.
If someone was looking for an HF focused SDR, and was considering equipment at the price point around a decent mid level traditional desktop receiver, say similar to an Icom R75 price point, I would say the Elad FDM-S2 is a good starting place. Along the price point of an entry level desktop, think Realistic DX-302 or Kenwood R600 when they were new, would be the Airspy HF+ or the AFEDRI. In the past I would have put the RFSpace SDR-IQ here also, but that radio is no longer in production.
While the price points may be similar, the SDRs will perform at least as well as their traditional price point equals. And besides performance there is capability, and the SDR brings a laundry list of capability no traditional receiver can come close to.
But at higher cost things get even better.
Both the Perseus SDR and the WinRadio G31DDC are simply very good, but at the price they should be pretty good. The RFSpace NetSDR is excellent, but no longer made. The G33DDC is world class, I mean seriously as good as any high end hobby / semi-pro RX of the past. The G35DDC is stunning, but to some people so is the cost.
So maybe some insight into the price point your friend is willing to go to? What are the performance expectations?
T!
