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PA2AGA > HDDIG 07.10.99 22:37l 171 Lines 6986 Bytes #-9727 (0) @ EU
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Date: Tue, 05 Oct 99 13:56:25 MET
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Subject: HamDigitalDigest 99/251A
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Ham-Digital Digest Tue, 5 Oct 99 Volume 99 : Issue 251
Today's Topics:
56k UHF-100W / 19.2K VHF -50W (2 msgs)
Caldera 2.3 and AX.25 Set-up
Great Heathkit site
HF RTTY (2 msgs)
Japanese packet radio hinted at on TAPR site.
Let's look at real numbers for TNC software sales (6 msgs)
Packet modems and Windows CE portables
TCP/IP over Flexnet ?
WTD Kenwood VC-H1 SSTV Communicator
WTD PTC-II Pactor Controller
Send Replies or notes for publication to: <Ham-Digital@UCSD.Edu>
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Problems you can't solve otherwise to brian@ucsd.edu.
Archives of past issues of the Ham-Digital Digest are available
(by FTP only) from ftp.UCSD.Edu in directory "mailarchives/ham-digital".
We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party. Your mileage may vary. So there.
Loop-Detect: Ham-Digital:99/251
----------------------------------------------------------------------
Date: Mon, 4 Oct 1999 10:18:08 -0700
From: "Hank Oredson" <horedson@att.net>
Subject: 56k UHF-100W / 19.2K VHF -50W
Paul Keinanen <keinanen@sci.fi> wrote in message
news:eTf4N75Xk2kSxK5rE7r41oDXWehP@4ax.com...
Just a couple amusing observations ...
> Why do you need a fade margin for a true line-of-sight path ? If you
> need a fade margin, it is not a true line-of-sight path anymore :-).
It is line of sight in the sense that we can see each other's antennae,
using high power binoculars or small telescopes, if it is not foggy
or raining as is usual most of the time here. However there are
the expected tropo refraction effects, particularly at 70 cm., which
may make the radio path very different from the optical path.
This is another "feature" of this area, a lot of inversions and strong
changes in air moisture from one place to another and one time
to another. We often have "capping inversions" that tend to trap
signals inside of valleys.
> Yes, this is true for the receiving antenna and with same size Tx
> antenna, the ERP is higher, so you should be able to compensate for
> the 5-6 dB extra loss with antennas of identical mechanical size.
> However, take care not to use too narrow beams, since this increases
> "coupling losses" into the scattering air volume.
I used to spend a lot of time working aurora on 2M. One thing we
noticed is that the large EME stations are not very good for aurora.
The small beamwidth does not illuminate enough of the scattering
regions enough of the time. My best aurora station used two long
yagis vertically stacked. Did not work well for short paths of course,
since all the power was on the horizon, but was exceptional for long
paths because the horizontal beamwidth was well matched to the medium,
and there was little power wasted to higher elevations. 1000 km.
contacts were easy, and 1600 km. contacts were possible, with
similarly equiped stations. Hard line, legal power limit, good preamp,
and well trained ears. All the usual "DXer" stuff.
>.
------------------------------
Date: Tue, 05 Oct 1999 08:56:07 +0300
From: Paul Keinanen <keinanen@sci.fi>
Subject: 56k UHF-100W / 19.2K VHF -50W
On Mon, 4 Oct 1999 10:18:08 -0700, "Hank Oredson" <horedson@att.net>
wrote:
>
>Paul Keinanen <keinanen@sci.fi> wrote in message
>news:eTf4N75Xk2kSxK5rE7r41oDXWehP@4ax.com...
>
>Just a couple amusing observations ...
>
>> Why do you need a fade margin for a true line-of-sight path ? If you
>> need a fade margin, it is not a true line-of-sight path anymore :-).
>
>It is line of sight in the sense that we can see each other's antennae,
>using high power binoculars or small telescopes, if it is not foggy
>or raining as is usual most of the time here.
Let me clarify my use of _true_ line-of-sight. On optical wavelengths,
if there is a visual contact, the Fresnel zone(s) are usually
unobstructed, since the zones are very close to the geometric line
between the end points. On a 10 km path the first Fresnel zone radius
for green light (550 nm) at midpoint is only about 37 mm. However, at
longer wavelengths, the zone radius is much larger and it is hard to
have sufficient clearance to keep the Fresnel zone above ground. On 70
cm, the required clearance at midpoint below direct line-of-sight line
would be nearly 42 m, thus if you now have just barely visual contact,
the antennas would have to be 42 m higher to have sufficient clearance
and that the simple path loss formula would apply. With insufficient
clearance, the path loss would be usually larger.
>However there are
>the expected tropo refraction effects, particularly at 70 cm., which
>may make the radio path very different from the optical path.
>This is another "feature" of this area, a lot of inversions and strong
>changes in air moisture from one place to another and one time
>to another. We often have "capping inversions" that tend to trap
>signals inside of valleys.
I have seen measurements taken at a place in which there is a clear
visual contact between antennas, but the lower part of the Fresnel
zone is hitting deeply into the ground near the receiving station,
with large signal variations at extreme weather conditions, so this is
not a _true_ line-of-sight path and thus you have to have a fade
margin.
Paul OH3LWR
>.
------------------------------
Date: 4 Oct 1999 15:29:14 GMT
From: Hamish Moffatt <hamish@rising.com.au>
Subject: Caldera 2.3 and AX.25 Set-up
In rec.radio.amateur.digital.misc J.T. Johnston <jtncarol@net1inc.net> wrote:
>>So where is the latest information? Should I switch to Redhat?
> Don't bother switching to RedHat. I am trying to set up RedHat for AX.25
> and am in the same boat. I came to the newsgroup hoping I could find some
> pointers. I'm also going to check out tapr.org.
I suggest y'all switch to Debian. Debian is 100% user-contributed;
it is developed by a community of interested people over the internet
and is not driven by any company. We have several hams in our midst
and have a mailing list debian-hams about ham radio software issues on
Debian. Craig Small, the developer of the new ax25-tools software,
is a Debian developer so we always have the latest ax25 tools.
73,
Hamish VK3SB (and hamish@debian.org)
--
Hamish Moffatt Mobile: +61 412 011 176 hamish@rising.com.au
To be continued in digest: hd_99_251B
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