George, are you saying the PRO has no means to vary the IF bandpass before
reaching the DSP? If you set DSP for 100hz bandwidth, does the IF bandwidth
remain wide open at it's default? The TS-870 has two rather wide band IF
amps with wide, 6khz crystal filters, and as I mentioned, they overlap as
greater selectivity is called for. Surely, the PRO has some means of doing
this...or does it? Educate me on this please.
Steve Ellington N4LQ.
----- Original Message -----
From: "George, W5YR" <w5yr@att.net>
To: "Steve Ellington" <n4lq@iglou.com>
Cc: "Stuart Rohre" <rohre@arlut.utexas.edu>; "N1EU" <n1eu@yahoo.com>;
<tentec@contesting.com>
Sent: Tuesday, April 02, 2002 8:00 PM
Subject: Re: [TenTec] what is "quiet"?
> 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
>
> All outgoing email virus-checked by Norton Anti-Virus 2002
>
> 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?
>
>
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