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PA2AGA > HDDIG 07.10.99 21:56l 174 Lines 6944 Bytes #-9727 (0) @ EU
BID : HD_99_249C
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Subj: HamDigitalDigest 99/249C
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Date: Mon, 04 Oct 99 07:06:47 MET
Message-Id: <hd_99_249C>
From: pa2aga
To: hd_broadcast@pa2aga
Subject: HamDigitalDigest 99/249C
X-BBS-Msg-Type: B
Paul Keinanen wrote in message ...
>On Fri, 1 Oct 1999 18:37:13 -0700, "Hank Oredson" <horedson@att.net>
>wrote:
> <Link usability times below 90 %>
>Which is MUCH better than having no link at all, where the usability
>>time is exactly zero.
>
>With usability times that low, the link is usable mainly to bulletin
>forwarders, for others, such links are much less usable.
>
>Paul OH3LWR
It's just that Oregon is really rough country up there -- or at least the
area north of Redding in California up into Oregon, It's painful just to
drive through -- let alone climbing up those cold mountains to put in
ham radio gear. Me, I'd get lost or fall off a cliff or get eaten by
bigfoot, (joke joke joke) there. Most of it is all
state parks or national forests, so could hams even get permission
to use this land? I don't think it's so productive to criticize people who
live in a place like Oregon, why they don't have fast line of site
links every 10km.
Maybe more interesting is whether these links are going to be
better than HF forwarding links. Because I would guess off the top
of my head that 90% reliabillty with an HF link of any kind is pretty
tough to achieve. It's always seemed to me that the reliability of
2meters to bend over a mountain top is slightly better than the
reliability of, say 80meters or something like this, for a similar
path. Still, maybe after a few of these hops, that HF starts working
better because of better range.
..
>.
------------------------------
Date: Sun, 03 Oct 1999 13:34:14 +0300
From: Paul Keinanen <keinanen@sci.fi>
Subject: 56k UHF-100W / 19.2K VHF -50W
On Sat, 2 Oct 1999 21:16:44 GMT, nomail@pe1chl.demon.nl (Rob Janssen)
wrote:
>Hank Oredson <horedson@att.net> wrote:
>
>>> With these directional antennas you don't need 100W, because if it does
>>not
>>> work with about 5W on UHF it will not reasonably work with 100W either.
>
>>Two posters have said this same thing. It is contrary to my experience,
>>on HF, VHF and UHF. Why 5W? Why not .5W or 5 mw? You see the
>>point? There is no magic "cutoff power level" involved. You simply need
>>enough power spread (ERP above receiver noise floor) to obtain the S/N
>>you need FOR THE PATH INVOLVED. Longer paths need more,
>>shorter paths need less. I do understand that you live where long paths
>>may not be required to build a network. Others live in places where
>>long paths (200 km and above) are in fact common. 20 db more ERP
>>gets you 20 db better S/N on any path with any system on any band.
>
>100 Watts are not required to build a 200 km path that is (nearly)
>line-of-sight. 5 Watts will do. Maybe 0.5W will, when enough antenna gain
>is available.
>
>Just calculate the path loss over such a distance and you will see that a
>5W signal is *very much* above the noise with bandwidths typical for
>today's packet radio network.
The path loss for a true line-of-sight path can be easily calculated
from L = 32 dB + 20log(f) + 20log(d), where f is in Mhz and d in km.
On 2 m a 200km path would have a path loss of 121 dB. A NBFM receiver
has a sensivity around -120 dBm, thus 1 mW transmitter power and
omnidirectional antennas should suffice. However, the background noise
levels on 2 m is still quite high, so maybe -110 dBm is required at
the receiver input, thus 10 mW Tx power would be required :-).
Such calculations are valid for true line-of-sight conditions e.g.
downlink from a high elevation satellite.
With ground base systems, even if there is a visual contact between
the antennas, the line-of-sight calculations are not accurate, since
usually the lower part of the Fresnell zone would be below ground,
thus increasing attenuation.
>You only need a lot of power when your path is through the earth, which
>means it will not be a reliable path anyway. Thus there indeed *is* a
>magic "cutoff power level": the power level you need to communicate across
>a path that is sufficiently open to avoid problems with propagation.
Looking at some path loss graphs from an old "The Radio Amateurs's VHF
manual", the path loss on 2 m for a 200 km path is less than 180 dB
for 50 % of the time. With -110 dB signal requirement (typical for
rural environment) and omnidirectional receiver antenna, +70 dBm or 10
kW ERP would be required. With 15 dB gain antennas at both ends, that
translates to 10 W transmitter power. With such a power, the link
would be expected to work for 50 % of the time.
Looking at the other graph, the path loss is less than 200 dB for 99 %
of the time, so 1 MW of ERP is required for omnidirectional reception
or 1 kW transmitter power for 15 dB Tx and Rx antenna gain. To reach
this reliability with 100 W of Tx power and allowing for some feedline
and power divider losses, four 15 element yagis would be required at
both ends.
The interesting thing is that the troposcatter path loss is nearly
constant at distances between 200 and 400 km, so the same setup should
be good for those distances as well. Thus, there is really a cutoff
power level that must be reached, in order to reach that far.
While the computations above give some estimates of the expected power
levels, the signal quality degradation (distortion) due to
troposcatter propagation may affect some modulation methods and
protocols more severely than should be expected from the path loss
figures.
Paul OH3LWR
>.
------------------------------
Date: Sun, 3 Oct 1999 07:49:33 +0100
From: Ian Wade <ian@dowrmain.demon.co.uk>
Subject: APRS Protocol Specification Draft now available.
FYI, the first draft of the APRS Protocol Specification is now available
for comment:
http://www.tapr.org/tapr/html/aprswg.html
73
Ian, G3NRW
--
+-----------------------------------------------------------------+
| Editor: RSGB's RadCom "Data" column. |
| email: g3nrw@arrl.net |
| AX.25: G3NRW @ GB7ZPU.#21.GBR.EU |
| |
| INTRODUCTION TO APRS: http://www.netro.co.uk/whitepaper.htm |
| APRS PROTOCOL SPEC: http://www.tapr.org/tapr/html/aprswg.html |
+-----------------------------------------------------------------+
>.
------------------------------
Date: Fri, 1 Oct 1999 16:14:39 -0400
From: "Nathan Ciufo" <nrciufo@one.net>
Subject: Help connecting TNC
Has anyone connected a Yaesu FT-920 to a Kantronics KAM for HF RTTY? I'm
almost done with the DIN plug soldering, and just wanted to double check
To be continued in digest: hd_99_249D
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