----- Original Message -----
Sent: Monday, November 28, 2016 11:36
Subject: [CrossCountryWireless] Sentry 5
prototype in the CQ WW CW contest
I mentioned a few days ago that I'd be running the Sentry 5 prototype in
the CQ WW CW contest as a final test before starting the production PCB board
I've always wondered if it would be possible to make a SDR transceiver work
full break-in on CW so that you can listen to the frequency in the gaps
between the dots and dashes. I have an old TenTec Corsair 2 transceiver in the
workshop that has full break-in and it's a simple elegant design that operates
The design of the Sentry 5 is such that on SSB, AM and FM it's a SDR
transceiver with the transmit IQ baseband signal sent to an IQ modulator to
generate the signal at the final frequency. For CW the local oscillator is
shifted LF by 750 Hz on transmit and the IQ modulator is unbalanced by a FET
with a timing circuit on the gate to generate the correct CW keyed waveform.
When the radio is tuned so that the beat note is 750 Hz then the transmitter
will shift to zero beat the incoming signal on transmit.
In the control circuitry there is a lot going on. There is a CW keyer with
the speed controlled by a slider on the Sentinel SDR program. There is also a
straight key option when one of the paddle inputs is shorted during
For the contest I decided to use the straight key option keyed by a USB
interface using the DTR pin controlled by the N1MM+ contest logging program.
For receive I used CW Skimmer controlling the Sentry 5 by CAT interface as a
Elecraft K3. The CW Skimmer program has an IQ input for SDR receivers so it
used the Sentry 5 receiver configured as a SoftRock-IF receiver in the
This allowed me to tune and change bands directly from CW Skimmer and
decode the CW and transmit using the macros in N1MM+. I would enter the
Assisted and QRP section of the contest as the power was set to 5W output.
So that's the technical set-up, how did it work?
On transmit I could hear between individual dots and dashes up to 18 wpm,
beyond that it was between the character spaces. As most of the contest I was
running at 28 wpm I could still here if another station was calling at the
same time or whether the station I was calling was calling over me. So the
break-in works, it just needs a bit more attenuation of the received signal
during transmit to reduce the click and clunks but that's a minor tweak.
I don't know how people can operate in a CW contest without CW Skimmer.
Some operators were operating above 40 wpm with many repeats and some morse
was bad with reduced spacings between the elements. My morse is very rusty, I
can copy the usual CQ, Test, AGN, and ? at any speed including my callsign as
a happy little tune but I can only copy callsigns correctly the first time at
12 wpm so I did need assistance. I used headphones to hear the signals to get
my timing right and also to try and improve my reading speed. I operated
search and pounce as my QRP signal would be too small for sitting on a
frequency calling CQ.
I thought I'd only make a few contacts but as usual I got carried away once
I found that it worked. I ended up with 289 contacts using just 5W to the
Terminated Inverted U antenna mainly on 40 and 20m.
I've attached a screen shot of the PC showing CW Skimmer, N1MM+ contest
logging program and in the background the Reverse Beacon Network Aggregator
that sent spots to the Reverse Beacon Network. This was just before I closed
down. CU4DX was a gotaway at 41wpm!