[VHFcontesting] FT897's, IF radios, etc

[James Duffey]

Chet - Thanks for the interesting note, which included this statement:

 "Software Defined Radios next? It will be interesting to do the numbers when
  the data is in for them."

Sherwood has numbers for several SDRs in his list:

< http://www.sherweng.com/table.html >

including the Flex 5000 and 3000 and the Perseus.

The close in third order intermodulation distortion (OMD) products turns out not to be a very good figure of merit for receivers based on modern analog to digital converters (ADC):

< http://www.sm5bsz.com/dynrange/qex/digital-imd.pdf >

< http://www.nitehawk.com/sm5bsz/pcdsp/dynmeas.htm >

as the third order IMD is pretty much independent of input signal level until the ADC saturates, so the third order IMD is pretty much dependent only on the dynamic range of the ADC used.

The Flex5000 and the Perseus have performance that is very close to the K3, and depending on the K3 filters used, can exceed the K3 performance. Of great interest, at least to me, is the third order dynamic range for the SDRs is independent of signal separation, the performance at 2 kHz is essentially the same as it is at 20 kHz.
 
While the K3 is a great radio, it is a bit deaf on 6M and to get reasonable performance in a quiet location one needs to add a preamplifier. Elecraft offers a very good one, I don't think that what that does to the third order IMD has been measured yet. They also are about to start selling a 144 MHz transverter that can be added to the K3. It is low power, 10W, and rather expensive, but if it is anything like their external transverters, it should have excellent performance.

The performance of the top 5 or 6 radios in Sherwood's list is excellent and I doubt that anyone would be disappointed in their use as IF radios for good transverters. Even the next 15 or so on the list are very good radios for transverter use. 

I have a friend who just got a Perseus. He proclaims it to be the best receiver he has ever used,a nod that includes some very good radios. It is not cheap, but if it is a harbinger of things to come in transceivers, our radios will just keep getting better. - Duffey
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KK6MC
James Duffey
Cedar Crest NM