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PA2AGA > HDDIG 28.07.00 13:41l 139 Lines 6234 Bytes #-9298 (0) @ EU
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To : HDDIG@EU
Date: Fri, 28 Jul 00 08:01:46 MET
Message-Id: <hd_2000_201A>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
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Ham-Digital Digest Wed, 26 Jul 2000 Volume 2000 : Issue 201
Today's Topics:
56Kb Packet Radio Modem (3 msgs)
Digipan help
KAM with 2AT Help...
Next Zakanaka beta release???
RigBlaster (12 msgs)
Rigblaster with Yaesu FT-840 Help Needed
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We trust that readers are intelligent enough to realize that all text
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policies or positions of any party. Your mileage may vary. So there.
Loop-Detect: Ham-Digital:2000/201
----------------------------------------------------------------------
Date: Tue, 25 Jul 2000 15:45:08 +0300
From: Paul Keinanen <keinanen@sci.fi>
Subject: 56Kb Packet Radio Modem
On Mon, 24 Jul 2000 08:36:54 +1000, "David Findlay" <nedz@bigpond.com>
wrote:
>Thanks for this info, I am probably going to build a WA4DSY 56kb radio
>modem, unless I can find a better design. Anyone know of what sort of range
>you can get? I need around about 50km. All stations will be withing a square
>surounding a digipeater, at a maximum of 25km away. They need to be able
>each others transmissions as it will be using an ethernet topology.
Ethernet style CSMA will not work reliably with such distances and
high speeds. In order to work reliably, omnidirectional antennas would
have to be used and in order to get the required ERP, quite high
transmitter powers would be required. My guess is that the 56 kbit/s
receiver will require about -110 dBm of receiver power. Looking at
some old troposcatter diagrams (The Radio Amateur's VHF manual,
1972), the path loss for 50 km and 99 % reliability is about 160 - 170
dB. Thus, a transmitter power of +50 .. +60 dBm (100 W .. 1 kW) is
required.
If you are going to use a digipeating station at a central location,
why not make it a network control station (master) which passes an
access token to each end user (slave) station. By doing this, there is
no need for a station to hear all other stations in order to avoid
collisions. While the master station still would have to use
omnidirectional antennas, all end user stations could use directional
antennas both for Rx and Tx pointing at the central station, thus
reducing transmitter power considerably. Thus, with 25 km maximum
range and 15 dB antenna gain, the required transmitter power is down
to a few watts.
If the end user equipment can operate split frequency (as any HT in
repeater mode), then only a ordinary phone repeater (with possibly
widened IF filters) can be used as the central station and ordinary
CSMA can be used at the end user stations with no need for special
master/slave systems. Any signal regeneration would be lost, but
assuming that the uplink and downlink paths are sufficiently reliable,
it should not be needed.
Paul OH3LWR
------------------------------
Date: Wed, 26 Jul 2000 08:27:46 +1000
From: "David Findlay" <nedz@bigpond.com>
Subject: 56Kb Packet Radio Modem
Could a single frequency be used? What about full duplex operations? I am
studying for a Cisco Certified Network Associate ticket and from that I have
learnt that token passing systems are often slow. I think I will just have
to experiment until I get a good solution and then just try to see what
works. Looking at a map I may not even need 50km. I still don't know how to
work mobile unless just having lots of digipeaters.
David Findlay
"Paul Keinanen" <keinanen@sci.fi> wrote in message
news:7brqns0l1rt1rqgoh8gciu7rggheo03iem@4ax.com...
> On Mon, 24 Jul 2000 08:36:54 +1000, "David Findlay" <nedz@bigpond.com>
> wrote:
>
> >Thanks for this info, I am probably going to build a WA4DSY 56kb radio
> >modem, unless I can find a better design. Anyone know of what sort of
range
> >you can get? I need around about 50km. All stations will be withing a
square
> >surounding a digipeater, at a maximum of 25km away. They need to be able
> >each others transmissions as it will be using an ethernet topology.
>
> Ethernet style CSMA will not work reliably with such distances and
> high speeds. In order to work reliably, omnidirectional antennas would
> have to be used and in order to get the required ERP, quite high
> transmitter powers would be required. My guess is that the 56 kbit/s
> receiver will require about -110 dBm of receiver power. Looking at
> some old troposcatter diagrams (The Radio Amateur's VHF manual,
> 1972), the path loss for 50 km and 99 % reliability is about 160 - 170
> dB. Thus, a transmitter power of +50 .. +60 dBm (100 W .. 1 kW) is
> required.
>
> If you are going to use a digipeating station at a central location,
> why not make it a network control station (master) which passes an
> access token to each end user (slave) station. By doing this, there is
> no need for a station to hear all other stations in order to avoid
> collisions. While the master station still would have to use
> omnidirectional antennas, all end user stations could use directional
> antennas both for Rx and Tx pointing at the central station, thus
> reducing transmitter power considerably. Thus, with 25 km maximum
> range and 15 dB antenna gain, the required transmitter power is down
> to a few watts.
>
> If the end user equipment can operate split frequency (as any HT in
> repeater mode), then only a ordinary phone repeater (with possibly
> widened IF filters) can be used as the central station and ordinary
> CSMA can be used at the end user stations with no need for special
> master/slave systems. Any signal regeneration would be lost, but
> assuming that the uplink and downlink paths are sufficiently reliable,
To be continued in digest: hd_2000_201B
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