[TenTec] what is "quiet"?

[George, W5YR]

Actually, Steve, the Twin Passband Tuning of the PRO (its version of IF
Shift and Passband Tuning and much more, actually) is not done with added
mixers or any analog circuitry. It, and every other signal generation,
modulation and demodulation, filering, noise reduction processing, etc. is
done digitally in the core DSP transceiver, operating at 36 KHz. The rest
of the radio consists of a minimum of down-converters and amps for the
receiver end and up-converters and amps for the transmitter. 

The Kachina is similar with a core unit at 40 KHz but the PRO uses a longer
wordlength of 24 bits instead of 16 and a 32-bit floating point processor
compared with a 24-bit fixed point processor. The results are very apparent
after using both radios side by side for many months now.

Although it is based upon multiple conversion architecture, the PRO and the
other Icom radios which now use that architecture - the PRO II and the 746
PRO - avoid nearly all the drawbacks of conventional radios like the 870
which still rely upon analog circuitry for signal generation, modulation
and demodulation, etc. We have seen a steady evolution in DSP designs
starting with those which "tacked on" a DSP processing unit at the tail end
of the radio usually at 11 or 14 KHz or so and did moise reduction and
filter formation there. Same thing could have been done at baseband, but
not as much marketing appeal.  <:}

The PRO design does a fair job of minimizing the ills of the RF chain, both
down and up, but they are still there, just not as pronounced as in other
designs. We had hoped that the PRo II would have improved matters, and it
did in some areas, but Nirvhana is not yet attained.

The K2 that I evaluated, and measured its audio/IF output spectra for all
modes and all filters, was actually quite noisy compared to my
expectations. The builder had incorporated some AGC mod that Elecraft
dislikes and that may have accounted for the lack of noise that others
describe. For its size, weight, and design, it is a remarkable radio, but I
have a hunch that the DSP-core-based 516 will outperform it in every area -
if it ever appears on the market! Certainly, it should outsell the K2
except to those seeking the kit-building experience. Much lower cost and
the potential for seriously better performance. I was especially
disappointed in the K2 filter responses; the passbands were quite irregular
and the ultimate rejection left a lot to be desired. Still, quite good for
a 7-pole crystal filter.

73/72/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437

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Steve Ellington wrote:
> 
> A friend of mine loaned me a K2 for a couple of weeks. I spent considerable
> time listening to it and IMHO, it does not fit into the same category for
> quietness as the R2, Triton, 1340, Conar etc. In fact, it reminded me more
> of something like a Corsair. QRN on 80m came through as a hefty roar.
> As for old boatanchors like HROs etc. George is right. They weren't very
> quiet. I've got a beautiful HQ-150 which holds the record for maximum number
> of knobs, 21. 2 RF amps, 3 IF amps, gain , gain, gain! Then after all that
> gain we have a crystal filter and Qmultiplier. By now, the guy on the other
> end has gone to bed.
> 
> Now as for this DSP business. DSP certainly adds some versatility but we
> shouldn't use it help mask a noisy RF chain. The TS-870, as good as it is,
> has several extra mixers which provide IF "slope tuning" which acts as the
> "roofing filter" prior to the DSP. Although it doesn't use those narrow,
> ringing, xtal filters, it still requires those extra mixers to do the slope
> trick. In cw mode, adjusting the DSP filter also activates the IF mixers to
> overlap two IF frequencies and produce a narrow bandpass. Of course this
> protects the DSP from being overwhelmed with strong signals. I assume the
> ICOM PRO works in a similar manner?