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PA2AGA > PACDIG 22.06.00 03:29l 144 Lines 6250 Bytes #-9411 (0) @ EU
BID : PR_2000_156B
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Subj: PacketRadioDigest 2000/156B
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From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : PACDIG@EU
Date: Wed, 21 Jun 00 18:53:03 MET
Message-Id: <pr_2000_156B>
From: pa2aga@pe1mvx.ampr.org
To: pr_broadcast@pa2aga.ampr.org
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Solar Data.
Come have a browse and enjoy !
http://www.bri1.btinternet.co.uk
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Date: Mon, 19 Jun 2000 13:37:17 GMT
From: No_Spam@No_Site.com (Alan - VE3NNM)
Subject: normal modem for packet
On 2000-06-18 sleesa@powerup.com.au said:
>Newsgroups: alt.ham-radio.packet
>X-Newsreader: Microsoft Outlook Express 5.00.2919.6600
>X-Original-NNTP-Posting-Host: ts57074.powerup.com.au
>NNTP-Posting-Host: grissom.powerup.com.au
>X-Trace: ozemail.com.au 961312350 203.32.8.130
> (Sun, 18 Jun 2000 17:12:30 EST)
>NNTP-Posting-Date: Sun, 18 Jun 2000 17:12:30 EST
>Organization: OzEmail Ltd, Australia
>has any body used a normal internal or external commercial modem
>for packet ....???
By "normal internal or external commercial modem", I'm assuming that
what you're referring to here is a regular dial-up telephone modem, and
not some kind of radio modem used in commercial services (ships,
airplanes, etc.).
None of the modes used by dial-up telephone modems are compatible with
packet-radio modems, with the exception of the 300bps Bell 103 or
v.21 mode. Even the telephone modem's 1200bps mode - Bell 212 in North
America or v.22 (?) in Europe (not sure about that one), are not
compatible with packet radio's Bell 202 mode (the packet and telephone
protocols use different modulation methoods for 1200bps). The
telephone's 1200bps mode would probably work OK over the air, though,
you just wouldn't be able to communicate with other packet stations.
(Might be useful as a secure inter-node or forewarding link.)
Although the telephone's 300bps mode is compatible with 300bps HF
packet, the phone-modem mode uses separate audio frequency pairs for
full duplex communication between the originator and the answerer of the
call, so the modem would have to be modified to transmit and receive on
the same tone pair in order to be compatible with packet. I believe this
could be accomplished using the telephone modem's loopback setting,
though. Then, all you'd have to do is hack into the modem and separate
the transmit and receive audio paths (somewhere around the
telephone-line coupling transformer) so you could gain access to the
proper circuit paths for your microphone and speaker or discriminator
connections. Are you sufficiently discouraged, yet?
Another issue to take into account is the fact that external telephone
modems and the "BayCom-style" packet radio modems do not use the same
pin assignments on the serial or "com port" connector. For example, the
BayCom packet format uses the Clear-To-Send line for receive data
instead of the com port's RXD line. You'd either have to hack the
modem's wiring to its serial connector, or use a special cable. You
would REALLY have to hack up an internal modem, probably have to do some
re-wiring to the UART. Probably more trouble than it's worth.
> is so will you pleas tell me the commands to
>allow it to be used as a straight thu modem like the old ones used
>to be .
If you're asking about defeating the Hayes-compatible AT-command set,
I know of no way of disabling that function in a modem. You obviously
would not have any way of sending an AT-command string to a modem after
its serial connections have been modified for packet. You *MIGHT* be
able to set the modem to Bell 103 with loopback and then program that
as the modem's default settings using AT&W0. You wouldn't be able to ATZ
the modem at the start of each session, but modems normally come up with
the default settings at power-up. If not, just re-initialize it (turn it
off/on). I haven't tried this.
I have obtained two Bell 202 telephone modems at an Amateur Radio flea
market. They are Universal Data Systems 202T models by Motorola. Bell
202 telephone modems are quite rare, primarily used in industrial or
retail applications (remote telemetry, re-ordering stock, etc.). The
ones I obtained had a two/four-wire telephone line selector on them, so
it was easy to separate the TX and RX audio paths (just run in four-wire
mode). I added a reed relay for the push-to-talk line, and hacked the
connections to the back of the serial connector to accept a standard
serial cable when running BayCom. Nice to have all those status lights
operating on packet just like when using a telephone modem, and it looks
a lot more professional than having those kit or homebrew BayCom boards
hanging off the serial port of the PC.
There was also an article on this back in the 80s in 73 Magazine. (I
couldn't find it at the time of my experiments, so I came up with my own
methoods, though).
I've picked up several of those pre-Hayes 300/1200 bps telephone
modems at Hamfests. My next project is to figure out those dip-switch
settings - if I can set them to Bell 103 loopback mode, it'll be fun to
see how they compare to the AM7910 BayCom modem on HF.
I've always wondered if 9600 or 14400 bps telephone modem modulation
could be used on a two-way radio link without corruption using a
BayCom-type serial hook-up. Same interface requirements as normal
high-speed packet of course (no simple speaker/mic connections at the
radio) but it's definately on my "stuff to try" list.
>Stewart
It's amazing how often ths phone-modem-to-packet question comes up.
Maybe someone oughta start a FAQ...
--
From the keyboard of Alan - VE3NNM (Kenora, ON, CANADA)
http://members.xoom.com/kenoraradio/
email: ve3nnm AT mailcity DOT com
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Date: Tue, 20 Jun 2000 03:22:58 +0200
From: "maria bonita" <mariabonita@gmx.ch>
Subject: normal modem for packet
> has any body used a normal internal or external commercial modem for
To be continued in digest: pr_2000_156C
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