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PA2AGA > PACDIG 22.05.99 04:00l 148 Lines 6698 Bytes #-9855 (0) @ EU
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Subject: PacketRadioDigest 99/113B
X-BBS-Msg-Type: B
(there are two of them). Information for this Commodore SX modification
comes from the article "My SX-64 runs Digicom!" in the October 1989
issue of "73 Amateur Radio" magazine, pages 24, 26 & 27. I have not
performed this modification myself, since I've been unable to find an
SX!
MY SUGGESTION: It's probably not a good idea to permanently jumper the
two RX DATA points together inside the computer, since operation of the
system could be affected when not running DIGICOM - make the jumper on
the modem itself. A five-pin DIN (Radio Shack CB microphone connector)
has just the right number of pins for this project - you can mount a
socket on the SX, and put a plug on the end of the packet modem's cable.
Use the DIN's barrel or shield for the ground connection, and that'll
leave you five pins for the supply, signal and control connections.
Never plug or unplug the modem with the Commodore's power turned on.
There were two different designs for the Digicom modem. The first one
appeared in the August 1988 issue of "73 Amateur Radio" magazine, on
pages 22, 23 and 75. It used an AM7910 chip from AMD and was
second-sourced by MOSTEK. It has not been manufactured for years, and is
hard to find. This was a multi-mode modem, and supported 300BPS packet
operation for HF in addition to the 1200BPS VHF mode. There is a better
version of this modem design from A&A Engineering circulating around
out there somewhere.
The second version of the modem appeared in the February 1989 issue of
"73 Amateur Radio" magazine, on pages 42 and 43. It used the more
popular TCM3105 modem chip from Texas Instruments, and is for 1200BPS
operation only. Due to a printing error, the PC board template in the
article was not reproduced on a 1:1 scale - it appears slightly larger
than it should be. See page 14 of the March 1989 issue if you need the
correct-sized template. I have had a lot of experience with this version
of the packet modem, and I can tell you to throw away the 100k
single-turn pot for the RX DATA calibration and install a ten-turn
version. It's adjustment is very sensitive, but when you find the "sweet
spot" you will be able to receive packets below the "full-quieting"
signal threshold. Forget any voltage measurements at the adjustment
point - the point is a very high impedance and even DVMs will corrupt
the measurement. Set the pot using an over-the-air packet test signal,
and gradually lower the audio into the modem as you make fine
adjustments to the pot. Once calibrated, return the audio level to
normal.
You can adapt any of the BayCom designs to the Commodore 64, as long
as you eliminate the serial-interface components and modify the power
connections that were used for that specific application. Just one
caveat: The TX DATA out from the Commodore cassette port was not fully
TTL compatible - its output was from a transistor, and peaked at about 6
to 7 volts. Make a voltage divider out of a 1k and a 1.8k resistor. The
high side of the 1k resistor goes to the TX DATA out from the Commodore,
and the cold side of the 1.8k resistor goes to ground. Connect the TX
DATA point of the modem chip to the junction of the two resistors. This
modification is NOT necessary for the SX, the logic level is fine since
it uses a connection directly to the SX's microprocessor (which is why
you NEVER want to use your SX's new "cassette port" to hook up the
cassette drive without aditional modifications!).
The software-based Data Carrier Detect feature of DIGICOM's version
3.51 was absolutely fantastic. It even beats the BayCom versions for the
IBM-PC in my opinion. If you want to run a BBS, use version 4.xx - but
you'll have to use the radio's squelch control since that version didn't
have DCD. Version 4.xx was actually an un-authorized "hacked" version
from a British Ham and was not recognized by the German DIGICOM team -
if I recall correctly. Did a great job, though! I ran version 4.01 for
some time, and found that the baud rate had to be set for 1165BPS in
order to communicate at 1200BPS in North America. The software always
assumed a 50Hz power line reference for timing, and so it had to be
slowed down a bit in 60Hz power areas. I found version 5.0 to be a
little buggy at times, and it included no new functionality over 3.51
anyway - unless you had a need for the 9600BPS firmware version that
required a special interface.
I have cross-posted my reply to the Commodore news group:
news:comp.sys.cbm
--
From the keyboard of Alan - VE3NNM (Kenora, ON, CANADA)
email: ve3nnm AT mailcity DOT com
http://www.voyageur.ca/~tokyo/
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>.
------------------------------
Date: Wed, 19 May 1999 18:48:54 GMT
From: "Robin Gilks" <gb7ipd@freeuk.com>
Subject: What exactly is TELNET?
TELNET is a communications protocol for terminal connection over TCP/IP.
You can use it over wires, radio, rubber bands or whatever your level 1
(hardware) layer supports.
What you use this protocol for is entirely host/user dependant - it is NOT
for downloading or whatever unless the system you connect to has that
facility.
--
73 de Robin. G8ECJ Hub manager gb7ipd
NTS: G8ECJ@GB7TVG.#42.GBR.EU AmprNet: g8ecj@gb7ipd.ampr.org
Internet: g8ecj@gb7ipd.freeserve.co.uk http://www.gb7ipd.freeserve.co.uk/
Shack: (+44) 1628 533311 Fax: (+44) 1628 850165
Club pages (g4xyw modem etc) at http://www.tvipug.freeserve.co.uk
Per Odegaard G0DJT/LA9GG <per.odegaard@btinternet.com> wrote in message
news:7hur56$4ts$1@mendelevium.btinternet.com...
> If TELNET goes by wire, then it's not _radio_ and should not be used
> ham _radio_ communications.
>
> 73, Per.
>
>
>
>.
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End of Packet-Radio Digest V99 #113
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