There are [or have been] several interesting threads running which
seem to be slowly converging into a good discussion of keying
characteristics of Pegasus/Jupiter [PJ's for short], Omni VI+, Icom
756Pro and also some general comments regarding key clicks, etc.
The thing I find interesting about the latest round of discussions is
that we are beginning to take the subjectivity out of the discussion
and are looking at some numbers that describe what we are hearing.
So in that spirit, I decided to run some tests on my PJ's much like
George, W5YR has been running on his Pro. In short, the PJ's look
pretty good. Perfect? No, but pretty good when held up in
comparison to the rest of the pack.
The test set-up consisted of my Jupiter running in both native
Jupiter mode and in Pegasus emulation mode. The Jupiter was
connected to a dummy load with a -20 db coupler to my triggered
oscilloscope. I operated the Jupiter with the internal keyer enabled
and had a Radio Adventures Co. CodeBoy keyer connected to the PTT
line on the accessory connector. The 'scope was being triggered by
the keyer output when I used the external keyer and by the RF
envelope when operating the internal keyer.
I am not done with the tests but here is what I have found so far.
Sidetone - Sidetone output timing from the PJ's EXACTLY tracks the
RF envelope, even to the point of having a smooth rise and fall time at
make and break. So, you don't really need to connect into the rf
output to know what your keying waveshape looks like. Just connect
into the line out and monitor the sidetone to see what the keying
timing is like. AND, you do not need any off air monitor to hear what
your signal is doing. Just listen to the sidetone.
Rise and Fall times - The rise and fall times are 3mS on all but the
first element in a transmission. The first element has a 2 mS rise
time on the first element and a 3 ms fall time. This finding exactly
duplicates the photos in the QST reviews as best I can tell from the
pictures. I was a little confused by this. This is QSK.......why would
the first element be different from any other? And, what is
considered a "first element"? I think I have the answer which I will
get into a little later.
Keying spike - Although difficult to see in the QST photos, the PJ's
do have a VERY SMALL keying spike on the first element. The first
element has about a 2% voltage overshoot which is a 4% power
overshoot! The percentage of overshoot remains constant over the
full power output range. So at 10 watts out, the overshoot reaches
10.4 watts and at 100 watts output, the overshoot hits 104 watts. I
cannot imagine this small amount causing any amplifier to trip or do
anything else nasty. Subsequent elements have a barely detectable
overshoot which is so small I can't measure it with any accuracy. I
believe the overshoot and the faster rise time of the first element
are related and I will get to that matter later as mentioned above.
Weighting - Here is where it gets a little complicated because of the
flexibility of the Ten Tec and N4PY control software user
programming and my ignorance. I am not exactly clear how to set
the user selectable weighting to "nominal" values, meaning values that
would yield the 1:1 and 3:1 dit and dah to space ratios. In fact, I got
bogged down on these tests and moved on to testing with an external
keyer. Basically though, the Jupiter was shortening the dits a
noticeable amount at very high speeds, speeds in the 60+ WPM range.
It also shortened the dits at slower speeds but, although
measurable, I could not detect it by casual listening at speeds below
30 WPM. I need to learn more about the setup though before I can
draw any meaningful conclusion other than, at the speed you usually
operate, set the weighting to a value that sounds good in the sidetone
and your signal will sound the same on the air.
External keyer - I confirmed something which may already be
broadly known here, that is, you can key the PJ's nicely by keying
the PTT line. I connected my CodeBoy both the official Ten Tec way
thru the key jack and the unofficial way thru the PTT line on the
accessory connector, and all measurements were IDENTICAL! That
is a nice undocumented feature. The CodeBoy has exactly 1:1 and
3:1 dit and dah to space ratios in it's default mode and that is what I
started testing with. When keying the PJ's, I noted a couple things.
First, the delay between key closure and RF [and sidetone] output is
20mS at all speeds. That can be seen in the QST photos. [I just
realized that I did not test for delay when operating split.....I'll do
that and report later]. BTW, this has nothing to do with keyer
weighting. This 20mS is the time required to shift internal circuitry,
most especially the PLL, from receive to transmit condition and is not
user adjustable.
Secondly, the dit to space ratio drops below 1:1 by a greater degree
as the speed increases, indicating that there are some uncompensated
timing issues in the firmware of the PJ's. However, the CodeBoy has
a "space" trimmer pot which when properly adjusted yielded a 1:1
ratio over the full speed range of the CodeBoy which is 10 to 40
WPM. In uncompensated form, the dah's became a little light at high
speeds but after the space adjustment, the dah's were again at 3:1.
At this point, using the CodeBoy, I have the recommended 1:1 and 3:1
ratios over the full speed range of the CodeBoy [which BTW exceeds
my speed range :-) ] and I have sidetone reflecting the transmitted
code elements exactly and I have Ten Tec QSK about which I need
say no more because it is hard to improve upon and I used too many
ands in this sentence. Sorry! :-)
Now.............about the rise time and "spike" such as it is, on the first
element. First of all, what is a "first" element? Since this is a full
QSK rig are not all elements a "first" element? NO, they are not!
The first element is the element sent after the rig has been at rest
for some period of time, maybe in the neighborhood of a second or
two. Ten Tec would know better than I what that time is. It is the
time in which the ALC circuit timing resets after sending elements. I
believe this explains the different rise time and the spike.
IMHO, one of the outstanding features in several generations of Ten
Tec rigs is the ALC stabilized output at ALL power levels. This
feature is present in the PJ's and I hope TT includes it in the new
rigs coming. BUT, there is one VERY MINOR drawback.......and that is
the effect on the first element. Let me repeat, the effect on the
first element is measurable but NEGLIGIBLE! It is a fly speck!
Here is what I think is happening. After resting, the ALC circuit is
reset. When the first key closure comes along, the transmitter is
running "open loop" with respect to ALC stabilized power output. TT
has very nicely built in a controlled rise time in the open loop mode so
key clicks are minimized. As the power is rising, it eventually hits
ALC threshold at which point the loop closes and stabilizes output
power at the set level. That transition from detection of ALC
threshold to stabilized output takes a finite amount of time and it is
during that time that the overshoot, the very small overshoot, occurs.
Once the ALC loop is closed, the transmitter system gain is reduced
by some apparently small amount and subsequent rise times are a
little longer as a result of the reduced system gain. This attention to
small detail is not found on may rigs I have owned and that have been
discussed here. A tip of the hat to Ten Tec as a friend of mine
would say. Can this be improved on? Sure.......at a cost. Does it
need to be improved on? In my opinion, not at all!
The rise and fall times of 3mS seem to be a good compromise too.
Short enough to create distinct elements to cut through QRN and
QRM but long enough to minimize key clicks, hence being a good
neighbor.
The PJ's are nice CW radios!
********REQUIRED DISCLOSURE************
I do not have a financial interest in Ten Tec except by virtue of
being a customer of both ham radio gear and OEM enclosures for the
CodeBoy and DigitalDial which my company Radio Adventures Co.
manufactures. Obviously I do have a financial interest in the
CodeBoy, a nice little keyer. :-)
**********PERSONAL NOTE*************
I commented early in this post about taking subjectivity out of our
discussions of some of these matters. I would like to qualify that
statement somewhat. Subjectivity is certainly important because it
pretty much tells us what we like and don't like about our gear. It
really doesn't matter much what the numbers say if I don't like this
thing! If I don't like it......I don't like it. Or.........If it like it,
so
what about the numbers. It is just that sometimes I think we go
rambling on talking about our subjective likes and dislikes almost as
though they were statistical, mathematical facts, when in fact, they
are simply likes and dislikes. So please understand that I know the
importance of subjective opinion but also I know the importance of
statistical fact. Both have their place in our discussions and I hope
more of us will take the time to dig through the rhetoric and find the
facts.
This is a great group. Keep up the lively discussions on all the
important matters like the dots, etc. :-) Oh, my Pegasus is black
and my Jupiter is red and my .................................... oh well, not
now.
maybe another time.
-73-
-Lee-
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