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PA2AGA > HDDIG 28.07.00 11:44l 178 Lines 6205 Bytes #-9300 (0) @ EU
BID : HD_2000_201B
Read: GUEST
Subj: HamDigitalDigest 2000/201B
Path: DB0AAB<DB0KFB<DB0CZ<F6KFG<DB0PSC<DB0ACH<PI8JOP<PI8ZAA<PI8WFL<PI8HGL
Sent: 000728/0700Z @:PI8HGL.#ZH1.NLD.EU #:65346 [Den Haag] FBB $:HD_2000_201B
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Fri, 28 Jul 00 08:01:54 MET
Message-Id: <hd_2000_201B>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
> it should not be needed.
>
> Paul OH3LWR
>
>
------------------------------
Date: Wed, 26 Jul 2000 10:25:28 +0300
From: Paul Keinanen <keinanen@sci.fi>
Subject: 56Kb Packet Radio Modem
On Wed, 26 Jul 2000 08:27:46 +1000, "David Findlay" <nedz@bigpond.com>
wrote:
>Could a single frequency be used?
Yes, that would be traditional digipeating. The problem is that you
have to receive the full frame before it is retransmitted. Also the
reply/acknowledge signal will suffer from this delay. If multiple
digipeaters are used to relay the message and end to end acknowledge
is used, the latency times becomes so huge, that the system is more or
less useless.
Remember also that in AX.25, the maximum data size is about 250 bytes
and at 56 kbit/s, the frame transmission times are below 50 ms, so a
very fast Rx/Tx turn around time is required.
>What about full duplex operations?
Full duplex is in principle only point to point, but if multiple
stations are required, the simplest solution is to use one master
stations with opposite frequencies, while the slaves communicate one
at the time with the master in full duplex.
Note that full duplex operation on a single amateur band will require
duplexers on all stations or the receive and transmit antennas must be
kept very far away from each other. Using different amateur bands for
the uplink and downlink simplifies the system, but some frequency
planning is required to avoid harmonics.
The use of a half duplex (phone) repeater is simpler, since only this
station has to operate in full duplex and require a duplexer if both
frequencies are on the same amateur band. The slave stations needs to
be able to receive on one frequency and transmit on an other, but not
at the same time, so no duplexer is required.
>I still don't know how to work mobile unless just having lots of digipeaters.
With normal AX.25 you are going to have a lot of "hidden transmitter"
problem, so the CS (Carrier Sense) part of CSMA will not work
reliably. You need some other mechanism to control when the mobiles
are allowed to transmit.
Note also that most amateur 1200, 9600 and 56 kbit/s are based of
narrow band modulation. These suffer from multipath (selective fading)
cancelling certain frequencies. When the vehicle is moving, the
frequencies that are notched out varies constantly and the narrow band
data stream fades to noise quite frequently or at least cause severe
phase shifts, corrupting the data. For reliable communication with
mobiles some modulation method with a large bandwidth (such as spread
spectrum, TDMA or COFDM) and strong FEC may be required, so that the
multipath notch will take out only part of the signal and the missing
part can be reconstructed from the ECC bits.
If you can guarantee that the mobiles are constantly moving, even
narrow band modes may be useful at least above 1 GHz, since the
multipath will take out the whole signal tens or hundreds of times
each second, so with sufficient interleaving and ECC, the burst errors
may be converted to random errors and reconstructed using the ECC.
However, if the mobile stops due to a traffic jam or traffic light, it
most probably will stop at a signal null and no communication is
possible, until the mobile moves some centimeters :-).
Paul OH3LWR
------------------------------
Date: Tue, 25 Jul 2000 08:47:04 -0400
From: Joe <jmowery@crosslink.net>
Subject: Digipan help
Check your computer time or the time zone you have set for
your computer.
ccom2@socket.net wrote:
> I was checking out the Digipan for PSK 31 but had a question , how do
> you set up the UTC time. it is wrong on mine?
------------------------------
Date: Wed, 26 Jul 2000 02:27:08 GMT
From: goroberts@adelphia.net
Subject: KAM with 2AT Help...
I have a KAM All Mode that has never been used. I have the cables that
come with it and need to connect it to an Icom 2AT. The instructions
that I have show using a mini-stereo plug, yet the 2AT just uses a
subminiature and a miniature mono.
The other side (HF) will get hooked up to an FT-900.
Anyone using this combination?
Glen
KE7FD
------------------------------
Date: Tue, 25 Jul 2000 22:17:25 GMT
From: "Casey \(KC\)" <casey@techie.com>
Subject: Next Zakanaka beta release???
Keep an eye on the Zakanaka eGroups list server
http://www.egroups.com/group/zakanaka
Better still sign up as a member. When the next beta 14 is available a
message will be posted to this list.
73.... Ken - VE5KC
--
KC's Amateur Radio Site - http://www.qsl.net/ve5kc/
KC's Canada Page - http://welcome.to/mycanada
--------------------------------
"Don Putnick" <dputnick@alumni.caltech.edu> wrote in message
news:h56f5.7532$ga2.187635@newsread2.prod.itd.earthlink.net...
> Any info on when that might be?
------------------------------
Date: Tue, 25 Jul 2000 08:16:33 -0400
From: "Bob Lewis" <rlewis@staffnet.com>
Subject: RigBlaster
> A ground loop is a circular connection of ground between two or more
> points
This is often a problem when you have long cable runs, especially
parallel with AC power runs, such as in commercial audio mic lines.
These loops are not a problem unless an AC signal gets magnetically
coupled into one of the lines. I wouldn't expect that to be the norm
for a 6 foot or less audio cable between the computer and the rig -
but maybe so. Even if it was, simply moving the cable should cause a
change in the hum level. Maybe there's something to be said for not
being so neat and tywrapping all your audio and power cables together
:-)
Just a thought - I wonder if these currents could be getting
magnetically coupled into the ground wire of the power cords by the
magnetic field around the hot and neutral wires. That could account
for major differences between computers/rigs, depending on the size,
balance and makeup of the different power cables.
------------------------------
Date: Tue, 25 Jul 2000 12:00:47 GMT
From: hamish@cloud.net.au (Hamish Moffatt VK3SB)
To be continued in digest: hd_2000_201C
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