Order Tray | Contact Us | Home | SIG Lists

Emergency comms. Was RE: [aprssig] Igates Are A Fair Weather Solution (was: "Finito")

Dave Baxter dave at emv.co.uk
Tue Aug 30 15:09:22 UTC 2005


> Maybe, but if those 150 to 250 stations are transmitting very often,
> your network is dropping a _lot_ of packets.

So what if a lot of packets are being dropped?  It's a UI, packets will
get dropped, but there are multiple transmissions of the same data from
the source, until it either gets an Ack back from the
destination/recipient, or the retry counter runs down, for "messages" in
any case.  In any event, the delay between them is (or should be)
random.  Yes, sometimes it doesn't get through, but for "Emergency" use,
why use the normal (busy) frequency anyway?  Best to use some other that
is quiet(er).

In any case, remember the FM "Capture Effect"  Even in the face of
extreme QRM, if a signal is strong enough to "get over it" with a decent
signal to QRM ratio, it will be registered and heard.  Yes, though that
then encourages some types to run 100's of watts, just to get an APRS
beacon heard 5 miles away, as often said, education, education and more
education etc.....

As to true emergency comm's.  You cant beat an "Experienced" CW
operator...  After all, isn't that what contests were to simulate?
Remember the KISS principle (Not the TNC mode!)...  Anyone remember the
recent "test" between CW and "Texting" shown on TV recently?  Have you
ever tried to enter anything "important" into the keypad of a TH-D7
while under duress (or mobile) or into a mobile phone for that matter?
It's not easy when you "have" to.  But, even I know two or three
accomplished CW op's who can do the "work the contest, make the tea,
sharpen a pencil, hold a voice conversation, and still follow what's
going on a few kHz up and down" trick, without breaking a sweat.  They
are the ones who should be encouraged to share their expertise.

Likewise, for long distance HF emergency comm's, if the gifted CW op's
aren't available, PSK31 does a pretty good job, where any form of packet
will just fail.  If all other options bomb, voice works well, and with
training, and following procedures, can be very very effective, so long
as the op's don't have handwriting like mine!

Packet in all it's forms, and perhaps APRS in some way more so, has a
use and a good one at that, but don't rely on anything that needs
reliable and clean power, as do most computer derived devices, yes
including PSK terminals! in the case of a true emergency, as no doubt
many are finding out in the south of the US at the moment, and not just
the "Amateur" networks I'd guess.

Here's one for Scot and the OpenTracker project.  Can it survive a
brownout reliably, or a short term dropout (less than that needed for a
full reset) without locking up, or corrupting stored data that was
waiting to be TX'd?  Not many (if any) of the "classic" TNC's can, that
I do know, and as for most things PC based, well...  OK, OK, yes yes I
know laptops have internal batteries, but what about the attached
TNC/Radio?  And the also "Attached" software.  Ui-View goes into abject
raptures if the TNC or D7 it's using, "burps"...

Enough....

Tin hat on, coat ready...

Dave B G0WBX.




More information about the aprssig mailing list