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Back from SW Division ARRL Convention in San Diego last weekend, one of the forum I particularly enjoyed was by Gordon Shackleford, AE6QW titled “Ultra High Performance HF Receivers: $1K to $18K Really?”. Like many of the forums there, this title is somewhat misleading. The presentation is about the anatomy of dynamic performance ratings of the receivers, like those listed in Sherwood Engineering’s Receiver Test Data (There is a link from this site). The top 12 are often referred as “Page 1 Receivers”. The top is Hilberling PT-8000A, an $18K system. The second ranked are, amazingly is a $1000 Elecraft KX-3, for some time. Now in Shackelford’s opinion (and I tend to agree) that this doesn’t mean KX-3 is a better rig than K3. He actually likes K3 a lot. But Sherwood’s ranking is heavily biased toward intermodulation immunity, and because KX-3 is a direct conversion receiver, there isn’t any intermodulation. But it has other weakness that K3 (or most multiple conversion radios) do not have, such as image interference reduction.
Nonetheless, among the top 12 radios, four are SDR type radios (Two from Flex Radio and the other, Perseus, a receive-only radio), and that’s saying something. The design difference between Elecraft and Flex Radio are also interesting.
KX-3 does a direct conversion, i.e., a local oscillation equal to the receiving frequency to derive baseband signal directly. It then uses a 24-bit A to D converter to feed the DSP.
Flex Radio, on the other hand, converts RF signal directly to digital. No local oscillator exists. Everything is processed digitally. Called Direct Digital Sampling, it is a brute-force approach, and requires a one-of-a-kind ADC device (developed with the cooperation by Analog Devices Inc) but for now, only 16-bit wide. That tends to limit the dynamic range thus the Sherwood ranking is lower (still at #11, it is impressive). But because of direct digital sampling, a lot of problem associated with KX-3 type direct conversion radios are not there. Shackleford calls it “the wave of the future”.
As of now, Elecraft and Flex Radio are two of the most interesting manufacturers of ham radio equipment, and on the exhibit floor, they made their presence known, side by side. It is the most interesting development in the recent decade. For now, Elecraft takes the lead, but we’ll see what happens in the next few years.
Another subject Shackleford was presenting, which is more a general interest, was about “moderately priced high performance transceivers”. He lists Icom IC-7410, Kenwood TS590S and Yaesu FTdx1200.
“Moderately priced” in his definition, is about $1,500. So similar FTdx3000 however of higher performance, was priced out. In particular, he was very interested in the way TS590 achieves the top 12 (it is at #12) ranking. The higher performance of better inter-mod immunity is achieved when down conversion (i.e., the 1st IF is below the receiving frequency) is performed, and TS590S does that selectively. All of these three radios achieves 110dB++ 2KHz blocking dynamic range, which is impressive.
Some sad facts are that several of those listed in top 12 are now out of production. Long live Te-Tec Orion II. Yaesu FTdx-5000D is out too, but is replaced by FTdx-5000 MP. Flex Radio 500A and 3000 are replaced by 6000 series, which is a bit pricey. But comparable to high end non-SDR rigs like FTdx-5000. Guess manufacturers are increasingly focused on medium range rigs, and that’s not a bad thing for many of us with limited budgets.