Hey Larry,

A small clarification. There are two types of AMTOR: ARQ and
FEC. The ARQ mode does involve error correction, but the FEC
(which is Forward Error Correction, not Full Error
Correction) does NOT. AMTOR B, which is FEC AMTOR, simply
sends each character twice. If that doesn't do it, the
character is lost or received erroneously.

73,

Chuck








Larry W4CSC wrote:
"thuss" wrote in
oups.com:


Larry,

I was under the impression that pactor II or III were far more reliable
and allowed faster transmission rates thank PSK31, is that incorrect?

Thanks,
Todd



Packet, Pactor, AMTOR (or its commercial cousing SITOR) are all
acknowledged modes. You send X characters to me....I add up the values and
send you an ack or nack to either resend more characters of the next group
or resend the old group again until I get it right. It's full error
correction. That's what the transmitter and receiver are doing all that
switching back and forth for. This is just great for binary file transfers
or something that just HAS to be perfect.

But, for text send/receive, it's not really necessary. However, for email
the header must be perfect or it isn't going to happen. So, yes, Pactor,
the chosen mode of the emailers, is necessary.

Now, if we were to set the same radios on 10 watts in Pactor and PSK31,
you'd first notice that PSK31 just keeps plodding along as fast as you can
type. No acknowledgement packets are sent or desirable. The transmitter
stays on the air until your fingers tire or you run out of things to type
about. Then, it's the other guy's turn and you keep receiving him.... IN
a packet switched type system, no matter what the name of the scheme, when
things go wrong, they go VERY wrong, resending the same "packet" or "group"
of characters over and over and over until the proper response is received
from the other end. In good conditions, it may be faster than PSK31 IF you
are a fast typist or are sending a text file. In bad conditions, it
amounts to ZERO as the conditions are too bad for perfect copy on the other
end. Some of the schemes reduced the number of characters per packet to
just a few letters before the ack attempt. This, of course, reduces the
transmit times and makes for poor throughput. Sitor/Amtor does this and is
painfully slow.

Unlike Pactor or the others, PSK31 is NOT an error-correcting digital mode
designed to transfer documents and binaries perfectly. But, as it costs
you NOTHING to play with, only the price of a cable from your headphone
jack on the radio to the line input of your soundcard and the download time
of a free software, you have nothing to lose in trying it.

The softwares have an audio spectrum display so you can pick which of the
little narrow PSK tracks for the software to decode and display. I invite
you to pick the faintest, tiniest, weakest track on the display to test
PSK31's capabilities. Pick one that fades in and out so you can see at
what point the errors start in the decoded display. On the HF bands, PSK
operators all hang out in about 1 SSB bandwidth, most notably 14.070 Mhz
carrier frequency USB. That's where you'll find the most stations to test
out your system.

I'd like to make another note while spewing my nonsense. DO NOT BUY THE
VARIOUS INTERFACE BOXES SOLD SO YOUR COMPUTER CAN KEY UP YOUR TRANSMITTER!
I've never had one! I'm using plain-vanilla, but nice ham radio equipment
that ALREADY has a VOX (voice operated transmit) circuit built into its
microphone electronics. PSK31 has no need of rapid on-off switching, like
pactor/packet/amtor/etc. If you simply switch the transmitter on manually
then click the XMIT button on the software to start the tone generation,
that works fine. VOX automates it as the transmitter will key up when it
hears the tone. Set the VOX delay to zero as you want the transmitter to
drop back to receive when the tone stops. Nothing could be easier. Hook a
simple 1K ohm volume control into the cable between the computer's audio
output (line out if you have it) and the transceiver's microphone input
wherever you can hook to it, even by unplugging the mic.


COMPUTER AUDIO OUTPUT---------|CW end
/
\ (wiper - center pin)
/--------------------MIC INPUT of radio
1K Pot \
/
GROUND CCW end

There's your total electronic circuit to use PSK31.....cheap!
Any old volume control pot between 500 ohms and 50K ohms works.
This only reduces the volume of the tones as mic inputs are low level, also
reducing hum by turning up the output of the computer and turning down this
pot towards ground to compensate. Just barely off ground is where most
dynamic mic circuits like it....just enough to get audio to key the VOX and
modulate the mic input. Audio to the computer is much less critical.

That and a copy of your choice in PSK31 software is all you need....and
total fun on very low power (10-20 watts max!), which makes the PSK bands
so many people can use it without interfering with each other.

Great fun, even if it won't email home. Home needs to get off their asses
and get their HAM LICENSES we've made SO easy to get, now!

Another note to ANY DIGITAL MODE......DO NOT FORGET TO UNPLUG THE
MICROPHONE! FCC TAKES A REALLY DIM VIEW WHEN IT HEARS AUDIO IN THE
BACKGROUND OF ANY DIGITAL MODE because whenever the transmitter is on, it's
transmitting that TV behind you on SSB while your digital tones are also on
the air! Some radios with "data inputs" for the tones DON'T disconnect the
microphone audio just because you plugged something into it. Test yours
carefully....