Ten-Tec definitely catered to the QSK CW crowd. I know that the Drake
4-line could be made to work QSK with an external T/R switch. Has anyone
on list done this and can comment on the QSK performance? Escpecially
how it compares to Ten-Tec's QSK.
Darrell:
I'm using my C Line in QSK mode with the help of: (1) Ameritron QSK-5 PIN
diode T/R switch; and (2) a PIC-based CW keyer. The keyer is the device
that establishes complete system timing. New keyers have the ability to
adjust the lead-in and tail times between the Keyed output and PTT line.
So, it's now possible to use classic separates in super-fast QSK mode. By
fast I mean near full-duplex. The supreme irony is that with this set-up
it's possible to attain significantly faster and seamless QSK with say...a
Heathkit DX-60 and Drake R-4B than a Ten Tec Orion II.
The system works around the existing C Line T/R system and requires no
equipment modification. Well, as an option one could bring out another
buffered PTT output from the QSK-5 to bias the T-4Xx transmitter when in SSB
mode. Or, just let Ip idle all the time.
An even better system is being developed between myself and a keyer
manufacturer. It will allow for independent lead-in and tail times such
that one can look at the keyed CW RF envelope on a scope and customize
timing to active the PIN diode switch moment exactly 1 msec before transmit
RF and 1 msec after the trailing tail of the CW envelope -- and that's
extremely important with Drake gear since the CW envelope rise in only about
2 msec, but has the classic grid-block keying characteristics of a long R/C
non-linear discharge as it asymptotically reaches zero.
This system only works for "separates." For the past thirty years,
manufacturers have had to compromise on QSK performance in order to contend
with PLL and synthesizer settling times. Transceivers generally use the
same oscillator for Tx and RX but the oscillator does not settle fast enough
between T and R to allow for super-fast QSK. That's why you see T/R
turnaround times in QST Product Reviews in the range of 10-30 msec, the
longest of which is the Flex-Radio gear. With the Flex, there's just too
much latency to achieve any semblance of QSK. Direct RF sampling shows the
best promise for future QSK performance from SDR transceivers as hardware
handles the lion's share of processing horsepower and not a Microsoft
Windows software application (e.g., PowerSDR).
The beauty of this system is that the PIN diode switch allows just enough Tx
to Rx leakage for one to get about a 10 dB over S9 signal on the receiver
while transmitting in CW. So, you're listing to your own signal in real
time and switching is so fast that your own signal is heard as just another
signal on the band. The Tx and Rx VFOs are free-running and do not have the
handicap of needing to switch by the amount of the CW offset between T/R
excursions.
Paul, W9AC
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