PSK-31 on VHF/UHF FM???
KC8PMX
on VHF/UHF and the simplicity of PSK-31, why cannot we use it those bands?
It seems to me from my limited understanding of how PSK-31 works, is that it
is relatively short bursts of information send in a tone that sounds like a
warbled whistle kind of sound. Granted FM does take alot more bandwidth,
but you are not transmitting all the time. Seems like this would be a much
more effective use of local (within state or from county to county etc...)
digital communications. Packet can seem to be buggy from time to time.
Please let me know if I am wrong, or if this would work or ??? I am fairly
proficient with packet now, and would be curious to explore PSK-31, but I am
limited to FM on 144, 220, and 440 but do have all-mode capability on 6
meters.
Thanks,
--
Ryan, KC8PMX
FF/MFR
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please)
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Dana H. Myers
KC8PMX wrote:
> With alot of non-HF people out there and the abundance of equipment for use
> on VHF/UHF and the simplicity of PSK-31, why cannot we use it those bands?
>
> It seems to me from my limited understanding of how PSK-31 works, is that it
> is relatively short bursts of information send in a tone that sounds like a
> warbled whistle kind of sound. Granted FM does take alot more bandwidth,
> but you are not transmitting all the time. Seems like this would be a much
> more effective use of local (within state or from county to county etc...)
> digital communications. Packet can seem to be buggy from time to time.
Actually, PSK31 is similar to RTTY, where stations typically take turns
transmitting in a half-duplex fashion and it is *not* packetized. Once
you start transmitting, you continue doing so until you're finished
typing whatever you intend to type. Further, PSK31 is used without
FEC or error correction, the idea being that one can tolerate some
amount of errors in a conversational keyboard-to-keyboard exchange.
If you stop or pause typing, you continue transmitting the PSK31
carrier until you start typing again or stop transmitting.
The actual bandwidth of the PSK31 signal is very, very small but it's
usually generated on a 1KHz (or so) carrier, which is frequency-translated
by an SSB transmitter and results in what appears to be a very narrow
PSK-modulated carrier (< 70Hz). Transmitting this as FM audio would result
in an FM signal approximately 7KHz wide for the same throughput, which
is terribly ineffecient and likely would not experience the same
resilience for low signal levels.
In other words, PSK31 doesn't make much sense for the use you
describe, though it's certainly possible (and I'm sure it's
been done already).
I don't know what you mean by packet being buggy in this case,
it's certainly sensitive to how people set up their signal
levels and TNCs, but, with a little care, packet is can be
quite good. The most common problem with packet I've seen
is people over-driving the transmitters into audio limiting -
it's better to turn the audio down a bit than it is to over-drive.
> Please let me know if I am wrong, or if this would work or ??? I am fairly
> proficient with packet now, and would be curious to explore PSK-31, but I am
> limited to FM on 144, 220, and 440 but do have all-mode capability on 6
> meters.
PSK31 as a local comms mode via an SSB transmitter on 6m might be
interesting, though.
Dana K6JQ
k6...@arrl.net
KC8PMX
"Dana H. Myers" <k6...@arrl.net> wrote in message
news:3CD03541...@arrl.net...
I understand that. But use in our WAAAAAAYYYYY under-utilized bands doesn't
sound like it would be problem. VHF and UHF are practically dead around
here.
>
> In other words, PSK31 doesn't make much sense for the use you
> describe, though it's certainly possible (and I'm sure it's
> been done already).
Well... yes and no.... If that is the only means I might have in an
emergency to communicate at the time, I might utilize it. Of course there
would have to be someone on the other end also.
>
> I don't know what you mean by packet being buggy in this case,
> it's certainly sensitive to how people set up their signal
> levels and TNCs, but, with a little care, packet is can be
> quite good. The most common problem with packet I've seen
> is people over-driving the transmitters into audio limiting -
> it's better to turn the audio down a bit than it is to over-drive.
>
Well... noise (any kind) seems to be a b*tch, for instance if a car with a
noisy electrical system drives by, or other interference like that.
>
> > Please let me know if I am wrong, or if this would work or ??? I am
fairly
> > proficient with packet now, and would be curious to explore PSK-31, but
I am
> > limited to FM on 144, 220, and 440 but do have all-mode capability on 6
> > meters.
>
>
> PSK31 as a local comms mode via an SSB transmitter on 6m might be
> interesting, though.
>
I was just curious if there was the interest in utulizing other digital
modes on VHF/UHF frequencies. I cannot speak for the rest of the country
but around here there is usually only band opening of 6m usage, next to
nothing on 220, fair to poor utilization of 2 meters and other than remote
reciever and other similar cross-banding type of work on 440, that band is
quiet too. I know that an FM signal is definitely a "wide" signal, but
there is still a lot of simplex frequencies that could be utilized in the
four main VHF/UHF bands. Also would be neat to experiment with it in the
900Mhz and 1.2Ghz allocations too.
The main problem with trying to operate SSB on VHF and above frequencies is
that there is little equipment available for such operation.
Ryan KC8PMX
charlesb
Some of the local hams were doing it this winter, and had fun with it. I'm
not sure if they were doing it on FM though. Best way to see if it works the
way you want is to give it a shot.
Why not?
You can turn off the error correction with packet (passall, etc.) and get
much the same effect. Instead of resends, you get garbage characters.
There is more advanced packet stuff now (FlexNet) that automatically adjusts
its own TNC parameters on a frame by frame basis (dynamic) so that
interference and retries are not so much of a problem. In the absence of
interference, the new stuff is much faster than old style packet, too. If
FlexNet notices that you have a good, strong connection, it will send 7
packet frames of 256 PACLEN every time your radio keys up. As soon as
conditions degrade though, and FlexNet has to re-send, it first backs off on
the parameters, sending less frames at a lower PACLEN until resends no
longer occur. Then after successfully sending several times with no resends,
it will experimentally bump the parms up a little bit, just to see if it can
get away with it. It's kind of fun to watch in action, and it is
significantly faster and more reliable than old style packet stuff.
Still, the idea of PSK31 on FM is interesting. You sure can't hurt anything
by trying, and it might be a lot of fun. I'd say go for it.
73 DE Charles, N5PVL
Gary Coffman
>> In other words, PSK31 doesn't make much sense for the use you
>> describe, though it's certainly possible (and I'm sure it's
>> been done already).
>
>Well... yes and no.... If that is the only means I might have in an
>emergency to communicate at the time, I might utilize it. Of course there
>would have to be someone on the other end also.
In that case you'd be better off just using FM voice. As Dana noted, the
problem with using PSK31 over FM is that the wide bandwidth of the
modulation negates the weak signal advantage of PSK31. In other words,
PSK31 works so well in noisy weak signal conditions because it is a very
narrow bandwidth mode (like CW Morse), and can take advantage of
very narrow receive filters to reject most of the noise and interference.
Using FM eliminates that advantage.
Of course if signals are good enough for voice communications on FM,
then PSK31 over FM will work too. But there's no advantage to doing
so. If you just want to play, then fine, but it doesn't bring anything particularly
useful to the table when used that way.
Gary