FSK on a K2?

[Ken Alexander-2]

Hi folks,

I'm thinking of getting a MicroKeyer from MicroHam for
my K2.  One of the attractions is that it claims I can
run FSK RTTY instead of AFSK.  Really?  I don't find
any mention of FSK with a K2 in anything I've
read...so either I don't know enough about FSK or I
don't know enough about my K2.  How do you do FSK on a
K2?

I'd also be interested in hearing from anyone using a
MicroKeyer with their K2.

Thanks and 73,

Ken Alexander, VE3HLS
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[Ken Alexander-2]

Hi Mark,

The main benefit to FSK seems to be not having to
fiddle with audio levels to and from the computer,
which are constantly being changed depending on what
I'm doing with the computer.  Other than that I don't
think there's any functional difference between FSK
and AFSK.

I went back to the MicroHam website and had a look at
the schematics for the cables they provide for other
transceivers (something I should have thought of
before) and I see that they show a dedicated FSK line
going to a multi-pin plug on some of the Icom cable
sets.  So, I guess the MicroKeyer provides the
capability for FSK on rigs that have FSK inputs like
your '820, but not on the K2.

That is unless they do some fancy tricks on the KIO2
line, which doesn't seem likely.

Thanks for your help!

73 - Ken


--- "Mark J. Schreiner" <[hidden email]> wrote:

> Some radios, back in their day, not sure about
> modern ones, had an input
> for RTTY.  It was a stereo plug or something
> similar.  Sort of worked
> like paddles do, but one side was for Mark and one
> for Space.  I
> remember my TS-820S had that.  Got me curious, so I
> just took a look, it
> was actually a 1/4" stereo jack on the upper right
> corner of the rear
> chassis and labeled RTTY Key, right next to a
> similar jack labeled CW
> Key.  The radio had a fixed frequency shift (maybe
> was selectable from
> under the covers for a couple of different
> standards) so that the Mark &
> Space would automatically frequency shift the proper
> amount when keyed
> with the correct interface.  No, your K2 doesn't
> have that, so AFSK is
> the method used for your K2.  If you get responses
> otherwise, let me
> know, though, however I am not sure I even could
> find any hardware to
> drive the Mark/Space correctly anymore!  Oh, I guess
> the MicroKeyer
> would, hence the purpose of your email, DUH!
>
> I'm not sure if there are any benefits to hardware
> FSK versus AFSK.  The
> "A" is really a method as they are both "FSK"
> regardless.  It seems like
> the benefit for AFSK would be the versatility and
> many software programs
> out there now that use a computer and soundboard to
> give the proper
> audio signals fed into your microphone connector to
> generate a multitude
> of modulation schemes from PSK31 and PSK63 to RTTY
> to Hellschreiber, and
> so on.  Used to be different hardware solutions
> required for different
> modes, now it is all done with computer and sound
> card.
>
> So, if interested, I have an old TS-820S for you to
> try if you would
> like to do "true FSK" instead of plain old "AFSK",
> just let me know!
>
> Mark, NK8Q

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[Ron D'Eau Claire-2]

FSK is FSK. That means the frequency of the signal shifts to encode the
data. The only difference is in how the FSK is created.

Half a century ago FSK was generated by shifting the frequency of the
oscillator that determined the transmitter's frequency. The usual approach
was to use a reactance tube or even a relay to switch a capacitor or
inductor in and out of the oscillator that shifted the frequency of the
oscillator slightly. (Think of very slow frequency modulation <G>).

The K2 is not designed for that form of FSK (or frequency modulation
either). Indeed the whole design is to prevent such frequency shifts
because, when they happen very slowly, we call it "drift"!!

But, by driving the K2 in SSB mode with an audio tone, the K2 generates
essentially *one* RF frequency: the carrier offset by the tone either above
(USB) or below (LSB) the carrier frequency. By shifting the audio tone the
one RF frequency produced by the K2 shifts accordingly. This produces FSK
that, at the rig's output, is exactly the same as that produced by the old
rig's shifting oscillator.

At the receiving end, nothing has changed. In the old days an FSK signal was
received and the beat-frequency oscillator (which made a CW signal audible
as a tone) was adjusted so you'd hear in the speaker an audio tone that
shifted in frequency.

In modern rigs designed for SSB, the product detector produces those tones
as well. There is *no* difference between the audio output of a K2 listening
to another K2 develop FSK using SSB mode and the audio output of a 1950's
receiver listening to a 1950's transmitter producing FSK by shifting the
oscillator frequency.

AFSK, Audio Frequency Shift Keying, is something quite different. It was
commonly used on VHF/UHF half a century ago and some use might still exist
today. It had a huge advantage for VHF/UHF because it did not require a very
stable transmitter or receiver. In the 1930's, through perhaps the 1970's it
was enough of a challenge to produce a stable enough carrier frequency on
the HF bands for critical tuning, much less on VHF or UHF. So, up on the
higher frequencies it was common to us an AM transmitter. The AM transmitter
produced a carrier and two sidebands just like a conventional SW broadcaster
or any broadcast band AM station does today. When tuning across such a
station, the only thing that changes is the strength of the signal. Unlike
SSB, tuning across an AM signal does not cause the modulation tones to
shift. A 1 KHz tone modulating an AM signal will be a 1 kHz tone at the
receiver, no matter the tuning. For that reason AFSK was very popular on the
higher frequencies back then. Conventional transmitters and receivers which
might drift hundreds of Hz during a single transmission could be used easily
to receive radio teletype (RTTY) using AFSK.

Today, some folks mistakenly call what we do on the HF bands with an SSB rig
(like a K2 equipped with the SSB module) "AFSK". They are partially right.
The output of their source, usually a computer, is an audio tone that shifts
in frequency. But their rigs produce true FSK as a result: an RF frequency
that shifts according to the modulation.

So the way to do FSK on a K2 is to develop audio tones within the normal
voice bandpass of 300 to about 2.1 KHz whose separation is equal to the
shift you need in frequency. Apply those to the K2's mic input and it'll
produce a shifting RF output or FSK. Today, those tones normally come from a
PC or special controller of some sort.

Ron AC7AC

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ken Alexander
Sent: Wednesday, January 31, 2007 6:46 PM
To: Elecraft
Subject: [Elecraft] FSK on a K2?


Hi folks,

I'm thinking of getting a MicroKeyer from MicroHam for
my K2.  One of the attractions is that it claims I can
run FSK RTTY instead of AFSK.  Really?  I don't find
any mention of FSK with a K2 in anything I've
read...so either I don't know enough about FSK or I
don't know enough about my K2.  How do you do FSK on a
K2?

I'd also be interested in hearing from anyone using a MicroKeyer with their
K2.

Thanks and 73,

Ken Alexander, VE3HLS _______________________________________________
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[k6dgw]

Ron D'Eau Claire wrote:
> So the way to do FSK on a K2 is to develop audio tones within the normal
> voice bandpass of 300 to about 2.1 KHz whose separation is equal to the
> shift you need in frequency. Apply those to the K2's mic input and it'll
> produce a shifting RF output or FSK. Today, those tones normally come from a
> PC or special controller of some sort.

You want to make sure the source of the audio tones [e.g. soundcard] is
producing two pure sine waves with no harmonics or other noise.  A
non-sinusoid audio tone will have other audio frequencies in its
spectrum, and each of those will produce an additional RF signal offset
from your suppressed carrier by its audio frequency.  A common source of
noise in the audio output of a soundcard comes from the switching power
supplies that power laptops.

I ran my K2/100 at 50W driving my LK-5002C amp to about 500W in the ARRL
RTTY Roundup, and it was a fantastic rig.  It takes a little while to
get the filters set up with CAL FIL, but once done, the real power of
the K2 RX really shows up.  I'll be back in the WPX RTTY coming up on
9-11 Feb.

And be careful ... RTTY is continuous duty when transmitting. At 50W,
the KPA100 heatsink got uncomfortably warm when I was in a good run and
transmitting nearly full time.  I wouldn't advise running more than half
rated power [7W for a K2, 50W for a K2/100] when running RTTY.

73,

Fred K6DGW
Auburn CA CM98lw
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