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Author Topic: Radio and Fax Machine  (Read 7184 times)

NN1I

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Radio and Fax Machine
« on: December 03, 2001, 08:25:12 PM »

Does anybody know how to connect a fax machine to a rig? I am curious if it is possible to use two fax machines on both ends of the communication between two amateurs (no phone line is involved).

Purpose: two emergency stations operate from the locations where they have standard fax machines, but phone line is not working.

73 Igor NN1I
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INITZERO

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Radio and Fax Machine
« Reply #1 on: December 04, 2001, 04:40:53 PM »

> I am curious if it is possible to use two fax
> machines on both ends of the communication
> between two amateurs (no phone line is involved).

In short, maybe, but not really.

While fax is a valid mode (http://www.hffax.de/,
for example), I'm afraid that making two generic
fax machines work with a pair of ham rigs might
be a bit difficult.

Most fax machines will not start a transmission if
there is no dialtone. Further, you'd need to figure
out how to key the respective radios for the
handshaking startup sequence. I'm sure it's possible
but I haven't seen any plans for making such an
interface nor a place to buy one.

You're also going to run into some bandwidth
limitations. Most fax machines run at 9600 bps
and can drop back to 4800, 2400 and 1200 bps
based on line conditions. Some high speed fax
machines can do 144,000 bps but that is more
unusual. On VHF/UHF, 9600 bps is legal (right?).
In HF, I think you'll be more limited.

Matt (k4mls)
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NN1I

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Radio and Fax Machine
« Reply #2 on: December 04, 2001, 05:04:41 PM »

That is what I thought. Sounds like I have to experiment myself.

First, I will consider emergency communications on VHF or UHF. So, bandwidth will not be the problem.

Second, one of my fax machines (Canon) allows to accept a fax during a phone conversation. So, there is a way around dialing and hand shaking.

Third, I will have to build a switch box for PTT operation and audio connections.

Any more ideas?

73 Igor NN1I
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INITZERO

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Radio and Fax Machine
« Reply #3 on: December 05, 2001, 11:24:41 AM »

> one of my fax machines (Canon) allows to accept
> a fax during a phone conversation. So, there is
> a way around dialing and hand shaking.

Dialing, yes. Hand shaking, no.

When the fax machine starts to connect, there is
negotiation as to what bit rate they will use and
the underlying protocol and fax quality. There are
several quick back and forth conversations before
the sending machine starts to stream.

Once streaming, you shouldn't have any problems.
However, I'm not sure how you are going to make
the initial setup converstation happen. It will
require a pair of radios with quick TX/RX turn
arounds and some way to get the radios to key. I
suspect VOX might be a start but only if it can
get the radio online quick enough.

When you get it working, please post a follow-up.
I'd be curios to see how it works.

Matt (k4mls)
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NN1I

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Radio and Fax Machine
« Reply #4 on: December 05, 2001, 01:35:05 PM »

OK, I am learning more stuff.

What about working split? Then each fax machine can transmit on one frequency and listen at the same time on another frequency.

I appreciate your input regarding this subject. I will consider all ideas. I am really curious, if it will work.

73 Igor NN1I
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INITZERO

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Radio and Fax Machine
« Reply #5 on: December 05, 2001, 02:13:16 PM »

> What about working split? Then each fax machine
> can transmit on one frequency and listen

    Ooohhh! I like that idea. Running full-duplex
could do it for you. That way you wouldn't have
to worry about TX/RX turn around times. Good idea!

    Matt (k4mls)
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NN1I

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Radio and Fax Machine
« Reply #6 on: December 17, 2001, 01:24:49 PM »

In 1995 PA3DJM claimed that he was able to send a fax (at 2400 bps) on 2-meter band using this interface

http://elektronika.vega.bg/radio/fax/faxif.gif

Right side of the diagram is simply a PTT contol which is optioanal if the rig has VOX.
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KG4ICG

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Radio and Fax Machine
« Reply #7 on: February 17, 2002, 06:47:40 PM »

 I think you miht be going about it the wrong way. SSTV is what you might want to do since basically a fax machine is sending a picture of documents thru the phonelines. SSTV sends pictures thru the airwaves, which are stills, not moving.
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WA4MJF

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Radio and Fax Machine
« Reply #8 on: March 17, 2002, 08:22:22 PM »

HAL (one ahead of IBM) in Urbana,IL makes a
device just for this purpose.

But hang on to your pocket book.

73 de Ronnie
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