Re: [amsat-bb] PACSATs & Kenwood HT

[Bob Bruninga <bruninga@xxxxxxxxxxxxx>]

On Sun, 21 Mar 1999, Garie Halstead asked about handheld PACSAT OPS using
the new Kenwood THD7 HT with built in 9600 baud TNC in RECEIVE ONLY Mode:
> 
> Being totally new to the PACSATs (and digital birds in general)...what
> kind of messages could one expect to download from a sat like KO-25 with
> the TH-D7A Bob?

WISP will capture every message in the downlink.  But it will only be in
the downlink if someone else is "requesting" it.  Thus the problem of
receive-only operation.  You will see plenty of BULLETINS and other
general messages to everyone, but you will never see a message to YOU,
unless someone else is reading it while you are monitoring!

We were considering several possibilities for working around this problem:

1)  Keep message to only a few words so that you could see it just in the
    subject line.  THus, you would get it in the directory listing.

2)  Bundle all short messages (about 1 line or so each to each mobile
    user into one "APRS MESSAGE" file.  Then have a ground station
    request that file on every pass.   The file would be updated by a
    gateway station on every pass so that it was always current with
    traffic for the mobile users.  Since it was always being updated
    and downlinked, receive only stations would have a good change of
    receiving it.  Conventional users need not fear.  An APRS message
    is more like a single line TEXT pager.  The entire APRS MESSGE file
    containing messages for say 25 mobiles would occupy less than
    2 seconds on the downlink....

> What would be the HT's downloading capacity on a single pass?

*** The HT here is only the radio and TNC.  The LAPTOP is doing all the
work.  I think typical captures approach a megabyte per pass, but to an HT
surrounded by buildings and trees, would see far less, maybe a few hundred
K.   But only the few K that you received 100% would count, unless you
monitored many more passes to slowly fill in the holes...

> After the download process, what proceedure does one follow in order to
> read what you've downloaded?

**** Its built into WISP.  Just slect the read option.  But again, you can
only read message files that were received 100%.

Lots of potential here....  Now that there are lots of these 9600 baud
HT's out there, its time to do some experimenting....

bob, WB4APR


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