[Icom] Rig advice

Fri, 21 Feb 2003 20:29:41 -0600

Keith, this topic has been covered extensively so forgive me if I do not use
a lot of bandwidth exploring it with you.

Let me first recommend that you visit the website of Adam Farson, VA7OJ, at

							http://www.qsl.net/ab4oj/

for a thorough discussion of the differences between DSP as implemented in
the PRO and PRO2 and in an outboard or internal audio processor. Some of my
material is on that site with a few comments on DSP as well so don't think
that I am putting you off by referring you to Adam's site.

Let me point out very briefly, though, that the PRO series rigs are
literally designed around  a DSP chip set. All signal operations are done
there mathematically: signal generation, modulation, demodulation, keying,
noise rejection, you name it. It all happens there at 36 KHz. The rest of
the radio is just a down-converter on the front end (the receiver) to get
from the r-f band of interest to 36 KHz for the DSP to get to work and an
up-converter (the transmitter) on the back end to get from 36 KHz back up to
the r-f band of operation.

On the other hand, radios NOT designed that way usually just tack on an
audio DSP operation at the tail end of the radio outside the AGC loop(s).
Usually the DSP processors are not all that powerful. At any rate, in that
location in the radio, they are inherently limited as to what they can do
and how well they can do it. I use the JPS NIR-12 on my IC-765 and Elecraft
K2 because they can benefit from what DSP functionality that the NIR-12
brings. But there is absolutely no comparison between the effectiveness of
the NR, for example, that the PRO can do and that which the NIR-12 provides.
Same with notching, bandpass filtering, etc. The NIR-12 is exceptional in
having as much or more processing horsepower (dual 40 MHz processors) than
any other outboard unit made. But it is still just a puppy trying to run
with the big dogs in comparison to the PROs.

So to try to summarize, anytime anyone on this reflector mentions the 756
PRO or PRO2 or the 746PRO, they are referring to the IF DSP core
architecture I described above. The original IC-756 had some limited DSP
capability at the back end, but nothing to remotely compare with what the
PROs can do. I will stick my neck out and say, on fairly firm technical
grounds, that there is no way that an outboard audio DSP unit can provide
the same degree of notching, bandpass filtering or noise reduction
performance that the PROs can. Being outside the AGC loop(s) is a major
reason, but there are others as well.

The outboard units have their place - helping the older generation of radios
that lack their capabilities - but they are no replacement or substitute for
the "real thing" designed into a radio which is literally built around a DSP
chipset.

Hope this hasn't raised your confusion level too much higher!   <:}

In parting defense of the K2, I have never heard Eric or Wayne or anyone who
knows and understands the K2 refer to the IF filter characteristics as
"terrible." The CW filter is unique is providing a switchable set of four
programmable passbands with a single set of crystals. While the passband
properties cannot begin to compare with those of  a PRO for shape factor or
ultimate rejection and the like, take it from me that the IF filters - CW
and SSB - are quite effective and "good enough" for the main purposes of the
radio. I have run spectra of the response of the K2 filters and compared
them with the 765 (loaded with Icom's finest crystal filters) and the K2 is
not that too much different. Hardly what I could term "terrible."

The K2 has some warts, of course - so does the PRO2 and any other radio
made - but taken overall it is an elegant, high-performance little radio
that has a world of uses. Mine sits proudly on the same desk as my 765 and
two PROs and gets more use than the 765 or the original PRO!

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of J. Keith Carter
Sent: Friday, February 21, 2003 5:46 PM
To: [email protected]
Subject: Re: [Icom] Rig advice

Hi George; I have great difficulty dealing with the use of the acronym DSP
when
it comes to defining the performance of a receiver. I purchased the W9GR
audio
DSP kit when it first was featured in QST many years ago. I used it with my
751A
and 735 for denoise and autonotch with great success and sold it only when I
purchased my IC-756 (original). BIG MISTAKE. The Icom DSP for denoise does
not
hold a candle to the W9GR regardless of what QST said in their road test. I
have
since found another W9RG and use it rather than the Icom denoise DSP and
keep it
in the line all the time to eliminate the background random noise and hiss.
Which brings me to my complaint. When one says DSP on this reflector when
describing the PRO or PRO II, Are they just quantifying the DSP IF filters
only?
IF so say so. Unless Icom have worked some miracles with their denoise DSP
in
the later models,( and I have compared a PRO ) I think the audio versions
can
compete and surpass. I guess what I'm saying is, Tell me what you're talking
about. I in no way contest the IF filtering characteristics of the Icom IF
DSP,
but there is great doubt relative to the denoise capability. The autonotch
seems
to be about the same when using the IF vs the audio. Just my humble opinion
when
reading the mail. Keith, VE3JKC. Incidentally the Elkel K2 IF filter
characteristics are terrible. Even Elecraft admits this. 73.