[amsat-bb] How to digipeat?

[Scott]

Hi Hans!

Like any digital mode, 1200 or 9600 packet requires several things to work
together using the correct settings.  This might run a little long, but
I'll be glad to outline them.

But first, one helpful thing to remember is that you want to treat the
uplink & downlink as completely separate affairs.  Depending on the
satellite, the uplink and downlink might find you using different bands,
different radios, different antennas, different software... at a MINIMUM
you'll be using different RF frequencies even if it's a simplex packet
digipeater since the doppler compensation will be opposite for up -vs-
down. (caveat - on 2m normal FM you can get by with sitting on one freq)
 To me it's always made sense to verify that you're 100% good to go on the
downlink, then set yourself up for the uplink.

So, if anyone wants to read on, here are the things to consider.

RF:  you'll need to know what the uplink & downlink RF frequencies are and
if either is in the 70cm band, doppler compensation is mandatory.  Here's a
tip: several of the newer sats are using NARROW-FM... even if you're
working on 2 meters, doppler compensation to/from a narrow-band satellite
radio is making a huge difference in my experience.  CAT control your radio
if possible; if not, then pre-program 5 memory channels the way most people
have their FM radios setup for voice satellite work.

MOD/DEMOD:  your radio needs to have a connection to your computer where
you run software set to decode the type of modulation in use by the
satellite.  On Windows, the various UZ7HO Soundmodem versions provide
perhaps the easiest interface to work with.  Direwolf is an option on
Windows, too, and by-the-way makes for a very easy to use iGate utility
running off to the side of your screen.  On linux, Direwolf is the most
popular option to my knowledge.  On either platform, of course we have to
find out from the satellite documentation what settings are required.  A
critical note that often prevents success on rates above 1200 baud is that
beyond that speed we need more audio bandwidth than is normally available
for general listening.  So, whether you're using a "real" radio or an SDR,
good rules of thumb are 3KHz of audio bandwidth for 1200 baud and 15KHz of
audio bandwidth for the higher rates.  On modern radios, that means using a
connection to the radio's "DATA" port for rates above 1200.  My TM-V71A,
for example, also has a menu option to switch between 1200 & 9600 - very
important!

USER INTERFACE:  as you mentioned, the UISS software is a great tool to use
as the interface when sending/receiving the packet modes.  It communicates
with UZ7HO Soundmodem or Direwolf to send/receive data to/from the
satellite.  But what to transmit?  We need that info from the satellite
documentation.  The "TO" is most often "CQ", but read everything you can
find about the satellite in question to be sure. (hint: monitor the
downlink & see what others are using!)  The "VIA" can be confusing because
many sats will respond to more than one name.  It all comes down to the
documentation - historically the 1200 baud APRS sats will answer to "ARISS"
which is handy... you don't have to change all your settings between
satellites.  FalconSat-3 is different; we use "PFS3-1" when transmitting to
FS-3.  "If" there actually is an active digipeater on BugSat-1, the team
has instructed us to use "LU7AA" as the call sign to access that satellite.
(I've tried BugSat-1 twice now but at the time of this post, have not had
any success)  As for the payload text to transmit, UISS helps a lot (for
APRS sats) by guiding us into sending properly formatted 'TEXT',
'POSITION', and 'MESSAGE' type APRS packets.  Monitoring the downlink and
seeing what message types others are having success with is helpful here.
Heck, everything I do on the sats is a copy-cat of the operating techniques
used by the operators that you see post repeatedly here, on Twitter,
QRZ.com, and elsewhere.   A huge 'thank-you' to all who share how-to info!

So, aside from individual considerations that are unique to particular
satellites (FS-3 is cross-band full-duplex, for example), that is an
overview.  If anyone has read this far, you have my sympathy.  I just
wanted to spell out what is common knowledge to most here on the chance
that one item might ring a bell and answer a question for you.  If the ISS
or either of the PSAT digipeaters would come back online, that would make
it a lot easier to practice with these modes.  As of the date I'm typing
this, all we have active over my location in the U.S.  are AISAT-1 (1200
narrow-FM) & FS-3 (9600).

Good luck!

-Scott,  K4KDR

===========================

On Sat, Sep 7, 2019 at 11:01 AM Hans BX2ABT via AMSAT-BB <amsat-bb at amsat.org>
wrote:

> Hello all,
>
> Apparently my mail about BugSat-1 raised some interest into that bird's
> digipeater. But that still leaves me with the following question (and I
> hope I don't sound too obtuse): how do you digipeat? I've tried to
> understand it by googling it over the past year or so, but I still don't
> get it much. Most tutorials explain about setting it up, but with HTs. I
> am running a home station only, with the rig connected to a PC. From
> what I understand you need to use the program UISS then.
>
> I got as far as this: I installed UISS (under Wine) and got it connected
> to Direwolf. Right now I can work the Falconsat-3 BBS using PacSat
> Ground Station and while running that program I see the same messages
> that Direwolf displays also appearing in UISS. So far, so good, but then
> what? I press either F5, F6, or F7, but nothing happens. Yes, my rig
> burps out some data for a split second, but I can't find myself back on
> APRS.fi. So what am I doing wrong? Any parameters to adjust? Or are
> digipeats not stored for the next iGate to put it on the internet?
>
> Again, I hope I don't sound too witless, but I've never really
> understood APRS, apart from terrestrial position reporting and even that
> was kind of hard with all the paths and whatnot. Hope you nice people on
> this list can drop some pointers. 73 de Hans
>
> P.S. I've got some nasty local interference on 145.825 MHz and that
> makes receiving the ISS and other birds almost impossible. I was lucky
> to get two frames in from IO-86 the other day, because that was due
> south, with the QRM coming from the north-east. Getting a signal up
> shouldn't be much of a problem, though.
>