Yes it is true that all Omni VI's have a very slight chirp. On a scope,
everything looks perfect. In fact, the keying shows up as the best ever while
in qsk mode. Unlike the imported rigs, there is no dit clipping and no spikes
on the first character. Some
older Kenwood rigs are able to match the keying ie. TS-930, TS-940 and the
Yaesu FT-1000MP comes close but has longer recovery time.
The best keying I hear on the bands today comes from old TenTec Triton IV's.
Over the years, more and more microprocessor controlled features were added to
most rigs increasing the need for delays in keying. Notice the scope
patterns in QST reviews. All rigs have a significant delay of several
milliseconds between key-down and rf output. Yes,
when you hit the key, you're not really keying the rig like we did 30 years
ago. Instead, you activate the processor which makes decisions about what
happens next. The sequence may go something like this:
1. Close key
2. Disable audio from AF preamplifier
3. Disconnect receive antenna input
4. Connect antenna to transmitter
5. Activate sidetone
6. Activate keyer
7. Activate transmit LED
8. Activate transmit oscillator
9. Reroute transmit osc. from rx to tx stages
10. Activate buffer and final amplifiers
11. Change display to show tx condition, rit etc.
The list goes on! The function and number of these events varies with design
requirements but as you can see, engineers
are no longer concerned with JUST keying an oscillator. From what I hear on the
air, most design time has gone into
programming and little concern is given to quality of the keyed waveform which
finally emits from the antenna jack!
When the Omni VI is keyed, the BFO oscillator becomes the tx oscillator. When
the key is depressed, the frequency of this oscillator is shifted to produce a
frequency offset. The amount of frequency shift and timing is again determined
by the
processor. While the oscillator's frequency is being shifted, it must not be
allowed to be heard on the air! However, there
is insufficient delay in the process and the last tail of the shift does show
up at the beginning of the RF output waveform and can be easily heard by the
receiving station. What is heard by the receiving station does vary. Using
sharper filters seems to accentuate the chirp and when the signal is weak, it's
hardly noticeable.
I've had two Omni VI's and probably spent a month experimenting with them in an
attempt to cure the chirp. My conclusion
is that the problem is caused by the processor not delaying the output enough
for the oscillator to stabilize. Although a delay
could be easily created by the programmers, the result would be slower tr/rx
changeover thus even slower QSK.
The older Omni V didn't have this problem probably because it's processor had
fewer task to perform resulting in better keying and faster QSK. Yes, the
factory is quite aware of the problem. Myself as well as several others have
talked to
them about it but no improvement took place in the Omni VI+. Apparently they
are comfortable with the keying although
it is in my opinion the worst on the air. That's why I went back to the Omni V.
Interestingly, many Omni VI owners are
in the denial stage about their keying. Some say they haven't gotten bad
reports so the problem doesn't exist. True, you
will seldom get a bad report however, the problems still exist. One owner
called me from K6 land because he didn't believe
me when I told him he had a chirp. I simply held the phone up to the speaker
while he keyed. He was dismayed over what he heard.
Please don't take this as personal. My entire station is TenTec. If the Omni VI
problem is ever resolved then I'll order a
VI+ but being an avid cw operator for 34 years who takes some pride in keying
quality I will not buy one until the keying
quality matches the receiver quality.
N4LQ Steve
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