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PA2AGA > HDDIG 07.10.99 22:23l 199 Lines 7210 Bytes #-9727 (0) @ EU
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Date: Tue, 05 Oct 99 13:09:52 MET
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From: pa2aga
To: hd_broadcast@pa2aga
Subject: HamDigitalDigest 99/250C
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Oregon, across the north ridge of Mt. Hood. Well over 200 km.
It ran at 5% packet loss "most of the time" unless a strong weather
front crossed the Cascades. Then we might lose the link for an hour
or so while the front passed. Yagis and 50W were enough. The path
did not work at all at 9600 baud of course, due to multipath.
One of the key things you need to do on HF is be frequency agile.
--
... Hank
http://horedson.home.att.net
>.
------------------------------
Date: Mon, 04 Oct 1999 06:56:47 GMT
From: Mike Wiley <nospam-wb5gmk@flash-nospam.net>
Subject: 56k UHF-100W / 19.2K VHF -50W
Closest thing Ive found to meet the speed is on www.symek.com a German
packet transceiver rather pricey, it's 20w on 440 but thats more than a
Paccomm. Haven't found anything out of the box for 19.2k on VHF. It's
43 miles WNW to OKC-shouldnt be a problem, 88miles ENE to Tulsa, Some
activity in ADA to SE. We don't have to have megawatts but peanuts wont
get over some of the hills either. It can't always be a single hop nor
can it be done by one person or one club. But to get I still think we
are going to have to speed things up or remain dead.
WB5GMK-Mike
Paul Keinanen wrote:
>
> On Sun, 3 Oct 1999 11:26:42 -0700, "Hank Oredson" <horedson@att.net>
> wrote:
>
> >
> >Paul Keinanen <keinanen@sci.fi> wrote in message
> >news:QiX3NzEKB4KJjELYJ9lrMd5Eleuc@4ax.com...
> >> On Sat, 2 Oct 1999 21:16:44 GMT, nomail@pe1chl.demon.nl (Rob Janssen)
> >> wrote:
>
> >> 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 :-).
> >
> >I'm confused. Didn't you forget to add in the desired S/N and the
> >fade margin requirement?
>
> I took the received signal power level from the BERR vs. signal power
> graph in ARRL handbook which was taken from an article by K9NG in
> August 1983 QEX. In those figures the S/N is factored in as the BERR.
> The -121 dBm gave 20 dB quieting and -120 dBm gave 1E-2 BERR, which is
> too low for AX.25, but might be sufficient for better protocols. At
> -116 dBm, the BERR was 1E-5 for both 300 and 1200 bit/s, which
> apparently has to do with the F2D modulation used. It is interesting
> to note that for 9600 bit/s the BERR curve was almost identical (using
> F1D) with 1E-5 at -114 dBm.
>
> 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 :-).
>
> >NBFM means 20 khz bandwidth? 9600 baud
> >maximum signalling rate? Three cases to consider: 1200 baud, 9600 baud,
> >and 56k (thus higher bandwidth, probably 100 khz. min).
>
> Sorry, I do not have figures for 56 k, but it was interesting to note
> how close the BERR for 300, 1200 and 9600 bit/s are.
>
> >Try it with a desired S/N of 35 db and 20 db fade margin.
> >(These two numbers were derived from the desired BER and link
availability.)
> >(Use others if you like.)
>
> Us I understand, the power level distribution figures include both
> long and short time fades, thus for practical purposes there is quite
> large fade margin in the 99 % figures.
>
> >Repeat for 70 cm.
>
> Troposcatter losses increase by on 5-6 dB.
>
> >We cannot run the 56k links on 2M in the US.
> >
> >One useful assumption: antennas on either band have about the same
> >capture area, i.e. they are about the same physical size.
>
> 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.
>
> >Going higher
> >in frequency helps the BER because more of the signal is on-path
> >and less is scattered by off-path reflectors
>
> On the other hand the relative bandwidth for a specific deviation
> decreases, thus deepening the multipath nulls. However, some
> artificial spreadening (e.g. direct sequence spread spectrum) might be
> useful to combat multipath.
>
> Paul OH3LWR
>.
------------------------------
Date: Sun, 3 Oct 1999 11:40:33 -0700
From: "Hank Oredson" <horedson@att.net>
Subject: 56k UHF-100W / 19.2K VHF -50W
Rob Janssen <nomail@pe1chl.demon.nl> wrote in message
news:slrn7vctvi.hlk.nomail@linux.pe1chl.ampr.org...
> I have been on holiday to the USA, must be about 10 years ago by now,
> and I was in your area as well. I had a 2M trx and packet equipment
> with me. The network was in the state described above: lots of nodes,
> connects to nearly all of them very slow. Connect to a BBS yields
> its welcome text, hardly can make it past the registration within the
> timeout.
Ten years ago there was essentially no network at all in this area.
A few digipeaters, two or three nodes which did not connect anywhere.
Node lists contained at most 5 or 6 entries
You must have been somewhere other than Portland, Oregon.
--
... Hank
http://horedson.home.att.net
>.
------------------------------
Date: Sun, 03 Oct 1999 17:33:49 -0400
From: Gary Coffman <ke4zv@bellsouth.net>
Subject: 56k UHF-100W / 19.2K VHF -50W
On Sat, 2 Oct 1999 12:12:55 -0700, "Hank Oredson" <horedson@att.net> wrote:
>Paul Keinanen <keinanen@sci.fi> wrote in message
>news:3bz1N7TpgqAjxYytjHzO95Z5qMeD@4ax.com...
>> On Fri, 1 Oct 1999 18:33:21 -0700, "Hank Oredson" <horedson@att.net>
>> wrote:
>> >
>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.
>>
>> What ???
>>
>> Do you really build that long link hops ?
>
>It is often at least 200 km. to the next ham interested in packet.
>Sometimes it is at least 200 km. to the next ham!
>We have a lot of "empty" in the Western US.
>
>> The average tropospheric refraction constant must be much different
>> over there. Over here, the sanity is questioned of anybody designing
>> over 100 km link hops :-), since such links would work reliably only
>> during some pre-dawn hours.
>
>Tropo is different depending on the terrain, weather conditions, etc.
>We don't choose to design such links, we NEED them, or we have
To be continued in digest: hd_99_250D
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