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[aprssig] Mic-E encoding on HF -- does generic SSID path GATE?

Robert Bruninga bruninga at usna.edu
Sun Aug 6 01:38:09 UTC 2006


>>> ben at ben.com 08/05/06 8:59 PM >>>
On Sat, Aug 05, 2006 at 01:35:07PM -0700, Dale Blanchard wrote:
> I am getting confused with all these do not and do paths.
> What exactly do I gave to program my tnc to send including the proper 
> commas, spaces, capital and call.
> I want to do some tests in the wilds of Idaho on 30 M.
> All I want is gated to internet/findu.com.
> No vhf.

To summarize this thread:

If you use relatively high power, odds are you need no path at all,
since you will probably reach an HF receiving station that is able to
IGate your packets directly.  Since you can easily cover half (or more)
of the country at high power on 30m, the no-path path is also fairly
insensitive to your location (ie fine for mobile use).

If you are using low to medium power (as I have been) then you will reach
fewer receivers on HF, and the odds that one will IGate you directly
goes down.  A path of ECHO (essentially RELAY or WIDE1-1 for HF) will
cause your packet to stay on HF and be rebroadcast.  Since the base
station is probably using more power than you, it will likely reach an
IGate-capable HF receiver and get to the internet.  However, in the
process you've at least doubled (depending on how many stations hear you
directly) the load on the low-bandwidth 300 baud HF APRS channel.  On
the plus side, if you are using a tranceiver (and not just a TX-only
"tracker"), you will probably hear your ECHO'd packet and know you were
successful.

Alternatively, you can use a path of GATE, which will cause each of the
HF stations that hear you directly to retransmit your packet on VHF.
There's a chance that any of the VHF stations to hear your packet will
IGate your packet.  You have no way to know if it worked without looking
on the Internet.  And, of course, you have used up some of the (less
scarce) 1200 baud bandwidth on 2m in the areas around any HF receiver
that heard you directly.  The bandwidth impact is also reduced because
each of the VHF "islands" around the HF GATE stations is independent,
unlike HF ECHO where every direct station is going to serially retransmit
on (the same) HF frequency.

And finally, if you're like me, you are only reaching one HF receiver,
which cannot reach any IGate-capable stations on VHF in one hop, so you
need a path like GATE,WIDEN-n (the one Bob just decried, although I think
without reading the rest of the thread for context).  The WIDE component
is whatever is required to reach an IGate from the location of the HF
receiver you reach directly.  Of course you don't know what is required,
any more than you do for any mobile tracker.  You can probably assume
that the HF GATE has a decent location, antenna, and power, so a WIDE1-1
(fill-in digi) is probably unnecessary, and the choices are between
GATE,WIDE2-2 or GATE,WIDE2-1.

All of the low power path options are going to be sensitive to your
transmit location.  If you cruise around the US with a 5w HF tracker,
sometimes you'll get IGated with no path, sometimes ECHO or GATE would
be sufficient, and sometimes only GATE,WIDEN-n would work.

So which solution results in the least QRM?  Why, not transmitting at all,
of course.  Sometimes when I read these path recommendations I think
people have prioritized bandwidth conservation above successful use of APRS.

-- 
Ben Jackson AD7GD
<ben at ben.com>
http://www.ben.com/

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