[Elecraft] QSK? Newbie question

Sat Oct 18 17:41:00 2003

The definition of QSK is:

"Can you hear me between your signals and, if so, can I break in?"

At least that the most recent iteration from the ARRL.=20

Within the lifetimes of many of us OT's, this sort of QSK was only a =
dream -
at best. Big coastal telegraph stations working ships at sea usually had =
the
receiver and transmitter sites separated by dozens of miles, so QSK was
simple. Indeed, they were often on different frequencies, necessitating =
some
sort of local sidetone to hear what they were sending.=20

But for those of us with a single transmitter/receiver site, it was a =
bit
more challenging. I know that up into the 70's, QSK was not the norm. =
Most
hams expected (and got) a 2 to 3 second delay after the other station =
sent
"K" before he could hear your signal. Of course, back then we ALWAYS =
sent
the call signs too - although it wasn't strictly required - so there was
plenty of time to make the switch. That often involved throwing a switch =
on
the receiver, a switch on the transmitter and sometime a third switch to
change over the antenna.=20

QSK stations back then used a number of schemes. Relays provided =
"semi-QSK"
but tended to be quite noisy. More popular were electronic switches,
normally using vacuum tubes. Often the antenna was permanently connected =
to
the transmitter and a vacuum tube was arranged between the antenna and =
the
receiver to protect the receiver front end from the transmitter RF. The =
most
common arrangement used a tube as a conventional low-level amplifier =
that
was heavily driven with TX RF so that it was "cut off" and stopped all
signals when hit with the transmit RF. That protected the receiver. A =
small
relay or second switch muted the receiver and keyed a sidetone =
oscillator.=20

The biggest problem with those schemes was the recovery time of the
receiver. It might take several seconds for the AGC to recover so it =
could
hear after transmitting.=20

I think that QSK in Ham rigs started to appear in quantity as an =
off-shoot
of VOX for SSB. That is, voice-controlled transmit for SSB phone =
operators.
In the late 60's and 70's VOX started to become commonplace, and =
emphasis
was placed on more fast-paced and "natural" phone conversations. Up =
until
then, a phone station (like a CW station) might hold a transmission =
lasting
5 or 10 minutes before passing it "over" to the next station. I used to =
hold
some massive "rag chews" lasting for hours with several buddies on 160 =
that
way, and it was rather entertaining to hear the "broadcast" various
operators would dream up. Almost like mini-radio "shows". And, since one
might be called to transmit only once every half hour or so in a round
table, one could putter in the shop, building and tinkering with gear =
while
listening to the other stations. For example, I remember one night when
three of us not too far apart set out to build a 2 meter transmitter and =
get
it on the air out of our junk boxes in less than half an hour so it =
could be
heard by the others - all while passing the transmission around the =
"round
table"!

Maybe that was part of the social impetus for VOX - when Hams stopped
building and found themselves sitting idle in front of a mic those long
transmissions grew too tiresome - both to make and to hear.=20

Anyway, getting back to QSK, early SSB rigs often offered CW as a =
"sideline"
mode, and the CW operation used the same sort of VOX automatic =
switching.
One couldn't hear between characters, but the rig automatically switched =
to
receive a second or two after the last press on the key. That was a HUGE
speed improvement over most stations of the day using separate =
transmitters
and receives. Those early systems were still relay driven by and large. =
A
few CW-only rigs - like the venerable Heath HW-8 QRP rig - used the same
system.=20

As solid state T/R switching became cheaper than relays for the
manufacturers it showed up in commercial Ham gear. AS soon as one wasn't
tied to the speed of a relay, the race was on for faster and faster QSK
speeds driven by ways to help the receiver "recover" faster and faster. =
To
what end this OT has never figured out, some ops today don't consider =
the
QSK to be "right" unless they can hear between dits!!=20

I have never sent so many dits that it was all that important to read
between them (if I could!) but I've grown used to be able to hear =
between
letters.=20

Ummm. What was the "stupid question" you wanted to ask. Never found it =
<G>.

Ron AC7AC

-----Original Message-----

Hi folks

I've a stupid question to ask. What is the significance of the remarks =
about
QSK operating in amateur radio? I've been used to a world where =
transmitters
and receivers are separate beasts and where the instantaneous muting of
multiple receivers and public entertainment systems is accomplished by
driving relays off the back contacts of a morse key.

cheers

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