[TenTec] Orion, NRD-545, DSP, filters etc

[George, W5YR]

Let me chime in on this one and agree with Harry, since I have been
investigating cw keying for some time now and have evaluated the PRO,
the PRO 2, the IC-765 and the K2 in some detail.

The problem that all the IF DSP rigs seem to face is the small but
finite time interval required to make the transition from receive to
transmit and actually get r-f coming out the antenna connector.

The PROs require about 10 msec to accomplish  this. As a result,
although the controller may be telling the keyer to send a string of
dots and calling for them to have equal duration with the spaces, that
10-msec delay in getting the r-f actually started, makes the dot/space
ratio less than 50%. How much less as a percentage depends upon the
absolute value of the space interval since the delay is constant but
the space duration varies with keying speed.

The effect varies in its importance according to the ear of the
listener, of course, but is primarily dependent upon keying speed. At
10 wpm, it is academic. At 20 wpm, the dot shortening can be heard and
readily seen on the scope. At 30 wpm and above, the dots are seriously
shortened and the keying takes on that "light" sound reminiscent of a
bug with the dot contact dwell time set too short. In other words,
"scratchy" to a discerning ear. Both PROs are alike in this respect.

On the other hand, both the IC-765 and the Elecraft K2 exhibit almost
perfect 50% dot/space timing at all speed ranges when in full QSK
mode. My 765 weighting is about 55% instead of the "ideal" 50% since I
prefer the sound of the slightly heavier dots. The 765 provides an
operator-adjustable knob to select the keyer weighting. However, it
affects both dot and dash durations relative to space durations so
heavier dots are accompanied by heavier dashes as well.

So, I concur that the PRO series radios have a CW keying problem using
their internal keyers. I get around this by using my Logikey K-3 CMOS
III keyer which provides two adjustments to correct the problems:

1. a fixed delay equal to the observed T/R delay in the rig can be
programmed into the K-3

2. the dot/space ratio can be independently adjusted.

I use a value of 10 msec for the first correction and find that to the
eye the dot/space interval remains constant at all speeds, as observed
by viewing the r-f output envelope on a scope. Since I prefer the
slightly heavier dot sound, I weight the dot/space ratio to 55%.

Unlike the 765 weighting control, the K-3 weighting affects dot/space
ratio only. But the 765 T/R time delay appears to have been
compensated for the full keyer speed range which is commendable. And
another reason why the 765 is still one of the premier CW
transmitters, in my opinion.

It is regrettable that such otherwise outstanding rigs as the PROs do
not have CW keying performance on a par with their other capabilities.
But, truth be told, it is unlikely that a great deal of attention was
paid to CW keying performance in the PRO design cycle. The only
operator adjustment for keying "weight" is menu control over the
relative *dash* length! This, of course, is essentially useless as a
compensation for the 10-msec delay effect. Perhaps someday Icom will
come to understand how to do CW keying in their IF DSP rigs.

For the "typical" Joe Ham running CW at 10-20 wpm, it is highly
unlikely that anyone would notice any deficiency in dot/space timing.
But, those who regularly move along at 25 wpm and up  may find the dot
shortening unacceptable - unless they and their QSO partners prefer
light dots!   <:}

It is for this reason, I believe, that the PROs have gotten a
reputation for being less-than-perfect CW rigs.That is unfortunate
since their CW receiving performance is better than any other rig I
have used, including the 765.  It would seem that some minor additions
in the firmware would allow this problem to be corrected, inasmuch as
the relatively tiny microprocessor in the K-3 does the job with no
problem.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489  IC-765 #2349 IC-756 PRO  #2121 IC-756 PRO2 #3235

----- Original Message -----
From: <DK2GZ at aol.com>
To: <tlogan7 at cox.net>; <tentec at contesting.com>
Sent: Tuesday, January 28, 2003 9:11 AM
Subject: Re: [TenTec] Orion, NRD-545, DSP, filters etc


> Hello
>
> did you ever look or listen on a second RX at your cw-shape forms in
qsk, when using a 756 proII?
>
> The RX maybe good, but the qso-partners maybe have problems
> to copy your choppy cw-sound in qsk.
>
>
> 73 de Harry, DK2GZ
>
> OMNI6+, K2/100, TS570D(G)