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PA2AGA > HDDIG 18.06.00 14:26l 171 Lines 7211 Bytes #-9439 (0) @ EU
BID : HD_2000_167G
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Subj: HamDigitalDigest 2000/167G
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From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Sun, 18 Jun 00 00:19:35 MET
Message-Id: <hd_2000_167G>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
> connections) or drops to maybe 1/200 distance in urban areas without
> visual contact (the 1/r^4 "rule").
So I would need one of the following:
1. Powerful transmitter
2. 300ft high antenna
3. Lots of repeaters
> With the quite low ham density, how many hams could you reach from
> your home station ? It has been notoriously difficult to get hams to
> support common infrastructure, the local repeater in your town is
> usually the only thing that can be done and get financial support from
> the local ham community.
Not many. In fact in the short term the only likely HAM to tune in will be
me, when I'm away from home and want to download the latest weather details.
Maybe a few storm chasers would also want to link in with mobile stations
for viewing weather info. I wouldn't want financial support from anyone. My
idea would be if you want it you build it and you pay for it. I would pay
for my gear my self. If some bloke down the street wants to join, he would
pay for his own gear.
> The other problem is multipath in situations when there is not a
> really clean line of sight path and where extremely narrow beam
> antennas are not used. Practically all amateur link are of this type,
> a good line of sight link is a rarity. Commonly used modulation
> methods, such as FSK and PSK do not work very well in multipath
> environment. To combat multipath, some form of spread spectrum or low
> symbol rate multicarrier systems such as COFDM is really needed. Until
> chips intended for both receiving and _transmitting_ DAB or DVB-T
> (which both use COFDM) are readily available, I do not think that
> there are going to be a lot of high speed ham connections.
I am not familiar with the modulation methods used by HAMs in packet radio,
but surely there would be some system that could be used. The most important
things would be to use some sort of manchester encoding or frequency
modulation. Multipath transmissions could be filtered out somehow.
> Practically all high speed connections require a full duplex
> connection (or a half duplex connection with very fast turnaround
> times), implementing this at high power levels (> 1 W) can be tricky
> and may require the use of different amateur bands for each direction
> with separate antennas for each band.
Couldn't you just do it like ethernet? Shared medium/frequency. Only one
station can talk at a time. If two transmit and the same time, this would be
detected by the transmitting stations, then one would pause, wait for the
other to transmit then continue. Checksumming would be definately required
and window sizes would have to be small(<100).
David Findlay
------------------------------
Date: Fri, 16 Jun 2000 17:37:51 +1000
From: "David Findlay" <nedz@bigpond.com>
Subject: Packet Radio
> It is not available as an off-the-shelf item in your local hamradio shop.
> Although you might get the impression that amateur radio is about
> experimentation, this is a description of the situation 20 years ago.
> Today, most hams only connect ready-built equipment and mumble about how
> they could never build it cheaper.
Where's the fun in that?
> The few projects that describe homebuilt 10 Mbit/s links are not at all
> suitable for broadcasting. They use frequencies similar to TV satellites,
> and the antennas for these frequencies normally have very small beamwidths
> and thus are only suitable for point-to-point use.
> To use anything resembling broadcasting, you would have to setup a network
> of point-to-point links with interconnecting nodes (routers).
This was sort of what I was thinking of. A few fixed location stations
linked together with something like CSMA/CD. They would use a single
frequency in a certain area. This would be similar to ethernet. When one
station transmited a packet, all would receive it and would then pass it up
the TCP/IP stack. If the data is for that station it is taken to a computer.
It could also allow multicasting, where a single packet could be sent to
multiple stations simulataniously saving bandwidth. If anyone is wondering,
yes I am trained in computer networking. Would anything that I haven't
thought of stop this sort of system from working, apart from some amateurs
not liking the idea?
David Findlay
------------------------------
Date: Fri, 16 Jun 2000 08:11:04 GMT
From: nomail@rob.knoware.nl (Rob Janssen)
Subject: Packet Radio
David Findlay <nedz@bigpond.com> wrote:
>> It is not available as an off-the-shelf item in your local hamradio shop.
>> Although you might get the impression that amateur radio is about
>> experimentation, this is a description of the situation 20 years ago.
>> Today, most hams only connect ready-built equipment and mumble about how
>> they could never build it cheaper.
>Where's the fun in that?
It is no surprise that the hobby is slowly dying...
>> The few projects that describe homebuilt 10 Mbit/s links are not at all
>> suitable for broadcasting. They use frequencies similar to TV satellites,
>> and the antennas for these frequencies normally have very small beamwidths
>> and thus are only suitable for point-to-point use.
>> To use anything resembling broadcasting, you would have to setup a network
>> of point-to-point links with interconnecting nodes (routers).
>This was sort of what I was thinking of. A few fixed location stations
>linked together with something like CSMA/CD. They would use a single
>frequency in a certain area. This would be similar to ethernet.
As I wrote (or tried to write): this is not practical at 10 Mbit/s.
The packet system at 1200 and 9600 bps works that way, but at 10 Mbit/s you
are really limited to point-to-point links. Dedicated equipment at each
end of the link.
See it as a leased line, not as an ethernet. You can build a large network
out of leased lines (like the Internet), but when you are not somehow on
the network (= have a link to another node that is on the network) you can
do nothing.
Rob
--
+----------------------------------+--------------------------------------+
| Rob Janssen pe1chl@amsat.org | WWW: http://www.knoware.nl/users/rob |
| AMPRnet: rob@pe1chl.ampr.org | AX.25 BBS: PE1CHL@PI8WNO.#UTR.NLD.EU |
+----------------------------------+--------------------------------------+
------------------------------
Date: Thu, 15 Jun 2000 17:07:10 GMT
From: "Aaron" <ahamilton2@sm.saddleback.cc.ca.us>
Subject: Pager Programming Pins
A little off the subject, but does anyone know the programming pins for an
advisor elite? Mine has two holes next to the battery cover lock, but I
need to know which is for In and Out and I need to know what it does about
the ground.
Thanks in advance.
--
___________________________________
Please send replies to:
ahamilton2@sm.saddleback.cc.ca.us
------------------------------
End of Ham-Digital Digest V2000 #167
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