I recently came across a CW Transmit problem while running the official Flex
1.6.1 code, and Eric at Flex has tried to replicate it but has not had any
luck. And I'm wondering if anyone else has seen it, or could keep a lookout
for it occuring.
The problem is this - sometimes (infrequently) when transmitting CW, the
Transmit RF envelope will look as though it has AM modulation on it, rather
than being a nice, clean continuous-wave envelope.
Why is this a problem, you may ask?
What seems to be happening is that, whenever the CW RF waveform appears to
have modulation on its envelope, what's really occuring is that the Line Out
Audio I & Q channels from the soundcard to the SDR1K radio no longer have a 90
degree relationship. The phase delta is something other than 90 degrees (and
this new phase value appears to be random).
The result is that I'm not just sending at one frequency, but two! For
example, if my CW Pitch is set to 600 Hz, I end up transmiting on both the
intended frequency and one 1200 Hz (i.e. 2 * 600) away. That is, I
simultaneously transmit on CWL and CWU, rather than on only one or the other.
Clearly this is not a good thing to have happen.
When it occurs, this envelope-type effect will continue as long as the unit
is in Transmit mode (affecting dots and dashes alike), but, if the SDR1000 then
returns to receive, chances are, when I transmit again, it'll be back to normal.
For example, I just ran a test on my radio. From the time I left Standby
mode, it took me 53 transmit-receive "cycles" (in which a cycle consists of
going completely back to receive before retransmitting) before the problem
occured. It then occured again after another 34 cycles, and then again after
another 83 cycles.
Later it occured twice within 22 cycles, and once after only 5 cycles - its
occurance seems to be random.
But it does occur, and because of that, it's keeping me off CW.
I've also replicated this problem with the 1.6.0 release, but have not seen
it with 1.4.4.
I'm running a stock Dell computer that I purchased from Flex along with my
SDR1K last October. The only other software that's running is my wireless
network software. And I'm using the Delta 44 card. So there's nothing about
my system which would appear to me to be out of the ordinary.
The radio itself is setup as follows:
Audio:
Buffer: 2048
SoundCard: Delta 44
Sample Ratte: 96 Ksps.
DSP:
Buffer Size: 2048 (but this doesn't seem to matter).
Keyer:
Primary: SDR
Secondary: None
Semi-Breakin: Enabled
Weight: 50
Ramp: 5 ms.
My paddles are plugged into the back of the SDR1K, and I've unchecked
"Iambic" so that I can use them as a handkey.
The only reliable way to observe if the problem is occuring is to monitor
your RF with an oscilloscope (although you may also be able to see the problem
if you have a good spectrum analyzer (or a second SDR1K)).
If you don't observe your RF waveform, you may never know if this problem is
occuring !
If you can monitor your transmit waveform, if/when this problem occurs you'll
see what looks like AM modulation on the CW envelope. (The "depth" of this
modulation varies with the "incorrectness" of the phase delta between the I & Q
signals.)
I'm stumped as to what could be the cause of this problem. I find it hard to
imagine that it's something specific to my system, given that the system is
"stock", but then again, who knows!
Any comments or suggestions would be welcome.
Thanks, and 73,
- Jeff, K6JCA
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