What does FSK sound like on an ordinary radio?
Liam Pratt
If you tuned into an FSK transmission (where a change in the
data bits is represented by a slight shift in carrier frequency),
what would it sound like on:
1) an ordinary AM receiver
2) an ordinary FM receiver?
Thanks a lot,
Liam.
Steve J. Quest
>
> If you tuned into an FSK transmission (where a change in the
> data bits is represented by a slight shift in carrier frequency),
> what would it sound like
I have a couple files that happen to contain valid software in
FSK on my website. The modulation is frequency shift keying of the carrier
frequency which you will hear in the beginning (the long tone). If you just
play them and listen to them, you'll hear what FSK sounds like, or you can
also upload the software into your older palmtop. :) The smallest file is
first. Anyone who started out (as I did) with a 50 to 110 baud acoustic modem
can enjoy these sounds as well, to bring back old memories of when text
scrolled EVER so slowly on our terminals. :)
http://www.code.archive.aisnota.com/pc3/Tandy_PC-3_Software2.mp3
http://www.code.archive.aisnota.com/pc3/Tandy_PC-3_Software1.mp3
http://www.code.archive.aisnota.com/pc3/
http://www.code.archive.aisnota.com/
Cheers!
sq
--
-<squ...@att.net>-\ ( ( | ) ) /--| Amendment 1 Congress shall make |\
===================> /_\ <===| no law abridging the freedom of |=>
Pirate Shortwave--/ /\_/\ \--| speech, or of the press. |/
Liam Pratt
>FSK on my website. The modulation is frequency shift keying of the carrier
>frequency which you will hear in the beginning (the long tone).
Hi Steve,
Thanks very much for helping out - tragically my PC is too slow to play
MP3s but would I be right in thinking I would have heard a thing called AFSK?
That is to say, a warbling between two audio tones which in order to be
transmitted would be modulated onto an RF carrier using AM?
What I was getting at was how "true" FSK, which flips between two nearby
RF carrier frequencies, must be demodulated. If you attempt to demodulate
it with an ordinary AM or FM receiver, what if anything do you hear?
Thanks again,
Liam.
Richard McCollum
"Liam Pratt" <nos...@freeserve.co.uk> wrote in message
news:9htj7t$km9$1...@news6.svr.pol.co.uk...
On VHF frequencies, it was customary to transmit tones, 2125 'mark' and
something higher called 'space' and this was done in the military pre WW2
when super-regens were the state of the art. This is AFSK. Common shifts
were 850 Hz, 425, and 170 coming later. At HF true FSK was the rule and the
receiver BFO (beat frequency oscillator) was used in the same manner as it
was used for Morse transmissions to produce the audio tones. Once the tones
are produced the receiving mechanisms are identical.
When SSB became the rule on military and amateur freqs, and product
detectors appeared in receiving equipment it became common to transmit audio
tones thru the mike jack of an SSB transmitter to produce FSK; from outside
the black box you cannot tell how the shift is accomplished and switching
audio is a lot easier. This is also the technique for PSK31 and the other
digital modes. Tune the receiver until the 'mark' gives you 2125 Hz and the
decoding begins.
So proper receiving requires SSB capabilities. On an AM receiver it is two
dead carriers and you may not even be able to detect the switching. FM
would have a similar effect-- at least it would not yield the tones. Some
form of product detection is required.
When they get back from vacation try http://www.rtty.com. They regularly
transmit old-style RTTY at 6994 and 13972 so you can try it out and hear it
for yourself.
Dick NØBK
Liam Pratt
> At HF true FSK was the rule and the
>receiver BFO (beat frequency oscillator) was used in the same manner as it
>was used for Morse transmissions to produce the audio tones.
OK, well I've used a receiver that has a "CW" mode (it picks up signals
where the carrier is being turned on and off and represents the 'off' state
by a beep); so if I listened to FSK with that mode, would I hear the two
carriers represented by beeps of two pitches?
>So proper receiving requires SSB capabilities. On an AM receiver it is two
>dead carriers and you may not even be able to detect the switching. FM
>would have a similar effect-- at least it would not yield the tones. Some
>form of product detection is required.
The same receiver also had a USB and an LSB mode - would either of them
do the trick?
Thanks,
Liam.
Ron Hardin
> When SSB became the rule on military and amateur freqs, and product
> detectors appeared in receiving equipment it became common to transmit audio
> tones thru the mike jack of an SSB transmitter to produce FSK; from outside
> the black box you cannot tell how the shift is accomplished and switching
> audio is a lot easier. This is also the technique for PSK31 and the other
> digital modes. Tune the receiver until the 'mark' gives you 2125 Hz and the
> decoding begins.
The Collins KWM-1 transceiver used an audio oscillator to produce CW from the
SSB circuitry, which would have been, when? in the late 50s.
That's not a result of product detectors in receiving equipment but a result
of SSB circuitry in the transmitting equipment.
An audio tone transmitted on SSB is the same mode as CW, just with a lot of
wasted circuitry, but circuitry that's already there.
--
Ron Hardin
rhha...@mindspring.com
On the internet, nobody knows you're a jerk.
Bill Meacham
>
> The same receiver also had a USB and an LSB mode - would either of them
> do the trick?
>
> Thanks,
> Liam.
Just as you have to tinker with the freq and BFO setting (fixed in your
case with the USB/LSB selector) to get properly detected audio on SSB,
you have to do the same for FSK tuning. Imagine a guy whistling on
SSB...the actual tone measured in Hz will change as you tune thru the
signal.
You can use either USB or LSB although the stock filtering in the radio
may not be ideal for FSK.
The old standard 2125/2975 (850Hz shift) isn't necessarily the most
common these days, but, on the good side, most FSK converters these days
will automatically detect the shift once you tune it in properly. And
most have decent audio filters so that operation is not totally
dependent on your radio's IF bandpass filtering.
--
Bill Meacham
Vieques, PR
Bill Meacham
> The Collins KWM-1 transceiver used an audio oscillator to produce CW from the
> SSB circuitry, which would have been, when? in the late 50s.
>
> That's not a result of product detectors in receiving equipment but a result
> of SSB circuitry in the transmitting equipment.
>
> An audio tone transmitted on SSB is the same mode as CW, just with a lot of
> wasted circuitry, but circuitry that's already there.
> --
> Ron Hardin
> rhha...@mindspring.com
I'm a little rusty on BAs, but did the KWM-1 really use A2 transmission
as opposed to A1? If so, then the CW signal would have been copiable on
an AM receiver.
I recall on the Heath HW-100/101 that they used the CW sidetone to key
the xmtr via the VOX circuitry, but it wasn't actually the audio
sidetone that was transmitted. Big difference between CW (A1) and
modulated CW (A2).
Mike Knudsen
<nos...@freeserve.co.uk> writes:
>If you tuned into an FSK transmission (where a change in the
>data bits is represented by a slight shift in carrier frequency),
>what would it sound like on:
> 1) an ordinary AM receiver
> 2) an ordinary FM receiver?
It sounds like galloping horse's hoofs. But often there's another AM carrier
close enough in your receiver's passband, to act like a BFO and let you hear
the two tones.
On an FM receiver it would sound even more like horse hoofs. But no "ordinary"
FM receiver tunes the SW freqs -- unless you consider Drake R8 and National
HRO-60 ordinary :-) --Mike K.
Life is a game. Play to enjoy!
Richard McCollum
> Thanks for your reply, Dick...
>
> > At HF true FSK was the rule and
the
> >receiver BFO (beat frequency oscillator) was used in the same manner as
it
> >was used for Morse transmissions to produce the audio tones.
>
> OK, well I've used a receiver that has a "CW" mode (it picks up signals
> where the carrier is being turned on and off and represents the 'off'
state
> by a beep); so if I listened to FSK with that mode, would I hear the two
> carriers represented by beeps of two pitches?
You got it. Copying CW with the beep in 'off' state would be interesting to
say the least. The old receivers used an AM detector but injected a little
signal ahead of it to produce a hetrodyne or 'beat note' (hence beat
frequency oscillator) for copying CW and it came in handy for FSK as well.
>
> >So proper receiving requires SSB capabilities. On an AM receiver it is
two
> >dead carriers and you may not even be able to detect the switching. FM
> >would have a similar effect-- at least it would not yield the tones.
Some
> >form of product detection is required.
>
> The same receiver also had a USB and an LSB mode - would either of them
> do the trick?
Appears you already have a product detector. I believe that LSB is the
convention when transmitting FSK but don't take that to the bank to cover
the overdraft.
Those two positions are for Single Sideband (SSB) reception, Upper SideBand
and Lower SideBand. SSB is a processed AM in which the carrier is
suppressed - it doesn't actually carry anything - and one or the other of
two identical sidebands is flushed for reasons of bandwidth. At the
receiving end you need to reinject the carrier to recover the audio. If you
encounter something while in AM that sounds like Donald Duck with a
headcold, try one of the SSB positions.
Most of what you hear on SW will be upper. The major exception will be the
amateur bands below 9 MHz, in your case 7-7.1 (7.3 in the Americas) and
3.5-3.9. The 3.9-4.0 segment available in the Americas is a cesspool.
You may find that putting the receiver in one of the SSB positions and 'zero
beating' (getting rid of the beep by tuning on the nose of the incoming
signal) will help AM reception. Try it.
Without having a clue about your intentions here, you should be aware that
most of the FSK you are going to encounter is encrypted or is not in the
Murray/Baudot format of days past.
If you have some decoding software, don't hold your breath.
>
> Thanks,
> Liam.
Dick
Richard McCollum
"Ron Hardin" <rhha...@mindspring.com> wrote in message
news:3B4264...@mindspring.com...
It is the preferred way to do CW today if anyone did any. The large
commercial transmitter used by W1AW to do their code practice does it
precisely this way. Good on-off keying of a large transmitter is not easy
at speed.
Yes, in a lot of ways it is using a drop forge to crack walnuts but it
avoids other circuit problems.
Dick
Richard McCollum
"Bill Meacham" <NOe...@coqui.net> wrote in message
news:3B427010...@coqui.net...
Bill, how does one tell the diff at the receiving end if I am pumping a
keyed carrier from my single sweep-tube Novice transmitter or a single tone
thru my Ten-Tec Pegasus? One and the same.
Bill Meacham
>
> It is the preferred way to do CW today if anyone did any. The large
> commercial transmitter used by W1AW to do their code practice does it
> precisely this way. Good on-off keying of a large transmitter is not easy
> at speed.
>
> Yes, in a lot of ways it is using a drop forge to crack walnuts but it
> avoids other circuit problems.
>
> Dick
Now, wait a minute Dick. Are you telling us that W1AW has been
transmitting A2 all along? I don't think so. If so, I've worn out a
switch for naught going into CW mode as I tune across the band and
happen across W1AW.
Maybe I've missed something for not being as active as I should be, but
I've yet to hear modulated CW (A2) even once in routine operating.
I have a problem with the ascertation that most Cw these days is MCW and
transmitters can't be managed at 'speed'.
Please clarify this and I promise I'll get myself up to speed.
--
Bill Meacham WX4A
Vieques, PR
Ron Hardin
> I'm a little rusty on BAs, but did the KWM-1 really use A2 transmission
> as opposed to A1? If so, then the CW signal would have been copiable on
> an AM receiver.
> I recall on the Heath HW-100/101 that they used the CW sidetone to key
> the xmtr via the VOX circuitry, but it wasn't actually the audio
> sidetone that was transmitted. Big difference between CW (A1) and
> modulated CW (A2).
There's no carrier so it isn't A2.
Bill Meacham
>
>
> Bill, how does one tell the diff at the receiving end if I am pumping a
> keyed carrier from my single sweep-tube Novice transmitter or a single tone
> thru my Ten-Tec Pegasus? One and the same.
Little difference until I use a sharp IF filter or do something silly
like turn the BFO off or jump into AM mode. Sure the sig is 100%
copiable, but the second that I hit the dial and see that you are
sending A2, I wonder why. I don't know the Pegasus any more than I do
the KWM-1 referenced earlier. If these rigs send A2 then its news to
me. I bet my normal settings for CW on my IC-745 would render an A2
signal invisible. Never heard one so I can't say definitively.
Bill Meacham
>
> Bill Meacham wrote:
> > I'm a little rusty on BAs, but did the KWM-1 really use A2 transmission
> > as opposed to A1? If so, then the CW signal would have been copiable on
> > an AM receiver.
> > I recall on the Heath HW-100/101 that they used the CW sidetone to key
> > the xmtr via the VOX circuitry, but it wasn't actually the audio
> > sidetone that was transmitted. Big difference between CW (A1) and
> > modulated CW (A2).
>
> There's no carrier so it isn't A2.
So explain how you get modulated A1.
-BM
Liam Pratt
>close enough in your receiver's passband, to act like a BFO and let you hear
>the two tones.
>
>On an FM receiver it would sound even more like horse hoofs. But no "ordinary"
>FM receiver tunes the SW freqs -- unless you consider Drake R8 and National
>HRO-60 ordinary :-) --Mike K.
Thanks Mike - I think that means I've never heard FSK. I do have an air band
radio which covers about 58-180 MHz but I don't suppose that counts as shortwave.
Cheers,
Liam.
Liam Pratt
>> where the carrier is being turned on and off and represents the 'off'
>> state by a beep)
>
>say the least.
Oh, did I get it the wrong way round? It seemed that the beep must mean
carrier off, because I tuned into the Rugby time signal on 60kHz and heard
a short beep every second. If a beep had represented the 'carrier on' state,
I would have expected to hear long beeps separated by very brief silences.
If you're not familiar with the Rugby signal there's a graph of how the
carrier switches on and off at http://www.npl.co.uk/npl/ctm/ctm001v03.pdf
>Appears you already have a product detector. I believe that LSB is the
>convention when transmitting FSK but don't take that to the bank to cover
>the overdraft.
I more or less understand the principle of SSB for speech; I did indeed hear
some Donald Duck conversations on AM, and as you suggested, USB mode did
usually resolve them. But what FSK has to do with SSB is not quite so
clear in my mind. Is the idea that you generate two audio tones (let's say
the 2.125kHz and 2.975kHz that you mentioned, Bill) to represent the 0 and 1
of your data, then feed that warbling sound into the mic of your SSB
transmitter, which will modulate the sound onto an AM carrier (let's say
7000kHz), but then remove the carrier and one half of the thingummyjig, to
leave you with 7002.125kHz and 7002.975kHz? (Or 6997.875 and 6997.025 if
you chose to use LSB.)
>Without having a clue about your intentions here, you should be aware that
>most of the FSK you are going to encounter is encrypted or is not in the
>Murray/Baudot format of days past.
Oh dear. I thought maybe there would still be some stuff for the general
public - weather maps, perhaps, or RTTY news reports. As for the demise
of the Baudot code, I'd heard that was just because people were switching
to ASCII.
Cheers,
Liam.
Ron Hardin
> > There's no carrier so it isn't A2.
>
> So explain how you get modulated A1.
> -BM
carrier exp(i*w0*t) times (=modulated by) audio exp(i*w1*t) equals
exp(i*(w0+w1)*t).
which is indistintuisable from a carrier alone at frequency w0+w1.
Richard McCollum
When you transmit a single tone thru an SSB transmitter, what comes out? An
unmodulated carrier -- you cannot tell on the receiving end whether it is
being done this way or with an oscillator and power amp. There is no
difference! Key the tone, key the carrier, machts nichts.
With FSK you shift between two tones and there is no way to tell on the
receiving end if I am keying tones or keying two rf oscillators. In W1AWs
case, if I push a 750 hz tone thru an SSB transmitter at 7039.25 USB or
7040.75 LSB you cannot tell it from a MOPA at 7040; it is still A1. Think
about it.
Dick
Richard McCollum
It is not A2, Bill. By keying a single tone into an SSB transmitter I put
out one rf signal.
Richard McCollum
> >Without having a clue about your intentions here, you should be aware
that
> >most of the FSK you are going to encounter is encrypted or is not in the
> >Murray/Baudot format of days past.
>
> Oh dear. I thought maybe there would still be some stuff for the general
> public - weather maps, perhaps, or RTTY news reports. As for the demise
> of the Baudot code, I'd heard that was just because people were switching
> to ASCII.
>
> Cheers,
> Liam.
>
>
Whether it is done Murray/Baudot or ASCII RTTY at HF suffers from selective
fading and a host of other ills which require either repeats or a 'good
guess' algorithm. Maritime TTY for example uses a system (SITOR) which
takes the 5-level Murray/Baudot and adds two bits such that there are always
4 mark and 3 space bits per character. This is used as the basis for asking
for repeats. Parity check if you are familiar with compooters.
On the ham bands at various times we have seen PACTOR (I and II), AMTOR,
CLOVER, G-TOR and the latest invention of one of your countrymen, Peter
Martinez G3PLX (probably descended from an Armada POW :-) ) is PSK 31 or
Phase Shift Keying in a 31 Hz bandwidth.
Weather satellites are relatively easy. They are not RTTY but rather fax.
In effect, the tone is not a fixed shift but wanders depending on what is
being transmitted. Our ARRL has a weather satellite handbook for $20 you
might actually get it cheaper thru the Radio Society of Great Britain.
Interestingly, it is largely a software problem; most multi-mode data
controllers handle everything from 66 baud RTTY thru 120 line or more FAX
(sometimes grey scale is a problem) needing only software to do a nice job.
And you can watch amateur Slow Scan Television as well because it is fax
under a different name.
Life has moved on since one did RTTY to the smell of burning machine oil and
SSTV on long-persistence CRTs.
Dick
Rich Griffiths
sigh).
The initial "A" designator now applies to double sideband, full carrier
emissions.
... Rich
Richard McCollum
"Rich Griffiths" <ri...@one.net> wrote in message
news:3B42FD5A...@one.net...
Liam Pratt
>SSTV on long-persistence CRTs.
Fair enough... shame though that just as I was beginning to understand the
simple stuff the world stopped using it...
What about the CW on-or-off question in my previous posting - can you shed
any light on that? Could the receiver be using a "beep = carrier off"
convention, or is that probably my mistake?
Thanks a lot,
Liam.
Richard McCollum
Just as a guess, I suspect you tuned an regular AM signal with a product
detector and simply heard the beep that was there anyway
Liam Pratt
>detector and simply heard the beep that was there anyway
Well the frequency was definitely 60kHz, which in the UK is reserved for
the National Physical Lab to send out their time signal from Rugby, and
the receiver was in CW mode. But not to worry.
Liam.
Peter J. Bertini
Peter
"Richard McCollum" <rmcco...@worldnet.att.net> wrote in message
news:DrC07.22809$C81.1...@bgtnsc04-news.ops.worldnet.att.net...
Richard McCollum
simple-minded. You also get some help by setting the carrier a tad outside
the passband of the filter. Having spent a lot of time adjusting carrier
balance controls I am happy those days are pretty much over.
It is for that reason, among many others, I am not too happy to see the
current crop of rice boxes do Antique Modulation so they can be sold to
CBers.
Dick
"Peter J. Bertini" <comm...@home.com> wrote in message
news:JaF07.135699$v5.10...@news1.rdc1.ct.home.com...
Bill Meacham
>
> I think "they" have changed all these codes on you, fellas (again,
> sigh).
>
> The initial "A" designator now applies to double sideband, full carrier
> emissions.
>
> ... Rich
I'm gonna have to go to the books on this and see what has changed. I
think we are talking about the same thing, just calling it by different
names.
I certainly agree with FSK being sent as 2 individual SSB audio tones,
but I'm not on base with the concept of CW being classified as a single
audio tone on/off transmission.
Michael Black
> Bill Meacham
> Vieques, PR
>
I probably should dig further into the thread, but one can get very
different results when feeding an audio oscillator into the mic
jack of a transmitter.
"Modulated CW", which used to be A2, was when a keyed audio oscillator
was fed into the mic jack of an AM transmitter. You'd commonly see
that in cheap walkie talkies for the 27MHz range, when they had a button
on the front for sending code. I'm not so sure how common the mode
was, but you would see it described in articles for use on VHF for
local use (expecially when the US Novice license lost voice privilieges
on 2M, but could still use A1 and A2).
Likewise, what used to be F2 was feeding a keyed audio oscillator
into an FM transmitter. You still see it, with CW ID'ing of repeate5rs.
Either of these give you a full carrier, and you are merely using
a code practice oscillator instead of a microphone to modulate the
transmitter.
Feeding an audio oscillator into an SSB transmitter does of course
give the equivalent of a simple carrier. The proviso is that the
oscillator has to be a clean sine wave, and the balanced modulator
in the transmitter has to be well balanced 9and the unwanted sideband
has to be eliminated). If one of these factors is missing, you will
get A2 modulation, ie a single tone on a carrier.
Michael VE2BVW
Rich Griffiths
>
> Rich Griffiths wrote:
> >
> > I think "they" have changed all these codes on you, fellas (again,
> > sigh).
> >
> > The initial "A" designator now applies to double sideband, full carrier
> > emissions.
> >
> > ... Rich
>
> I'm gonna have to go to the books on this and see what has changed. I
> think we are talking about the same thing, just calling it by different
> names.
Yeah, I think so too. I agree with the substance of what you guys are
saying. I just had to throw in that bit of trivia.
> I certainly agree with FSK being sent as 2 individual SSB audio tones,
> but I'm not on base with the concept of CW being classified as a single
> audio tone on/off transmission.
> --
>
> Bill Meacham
> Vieques, PR
The regs recognize for a whole bunch of ways to generate CW or FSK. The
definitive part of the code for these modes is the third character: an
"A" or "B" (= telegraphy) for CW or "D" (= data transmission) for FSK.
One of the many ways of generating CW is single-sideband, suppressed
carrier with a single channel containing quantized or digital
information on a modulating subcarrier transmitting telegraphy
(designated code J2A). The corresponding designator for FSK generated
by SSB is J2D (I think).
It all seems rather absurd to me.
... Rich
Bill Meacham
> The regs recognize for a whole bunch of ways to generate CW or FSK. The
> definitive part of the code for these modes is the third character: an
> "A" or "B" (= telegraphy) for CW or "D" (= data transmission) for FSK.
> One of the many ways of generating CW is single-sideband, suppressed
> carrier with a single channel containing quantized or digital
> information on a modulating subcarrier transmitting telegraphy
> (designated code J2A). The corresponding designator for FSK generated
> by SSB is J2D (I think).
>
> It all seems rather absurd to me.
>
> ... Rich
I checked out the FCC site for the 'new' emission designators. What
used to be so simple is now pretty complicated since they use two
different systems.
http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=47&PART=2&SECTION=201&TYPE=TEXT
-and-
http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=47&PART=90&SECTION=207&TYPE=TEXT