[amsat-bb] Thoughts on ISS packet switch back to 145.825 MHz (long)

Robert Bruninga bruninga at usna.edu
Sun Apr 16 18:28:21 UTC 2017

I agree completely.  ISS digipeting should be for LIVE operators.  Or for
LIVE things.... (a student experimental ocean going buoy for example)...

NOT for non-moving-fixed egos...


-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Patrick
Sent: Saturday, April 15, 2017 7:51 PM
To: amsat-bb at amsat.org
Subject: [amsat-bb] Thoughts on ISS packet switch back to 145.825 MHz


Earlier today, I tweeted a quick comment about what I saw on the ISS
145.825 MHz digipeater just after 1900 UTC this afternoon. Since tweets
are limited in length, I'm posting a longer message here...

In the past few weeks, once word got out that a replacement for the failed
Ericsson VHF HT on the ISS was being sent up to the station, many were
anxiously looking forward to seeing the ISS digipeater move from 437.550
MHz back to 145.825 MHz, where it had been until the old radio's failure
in mid-October 2016. I understood that many would welcome this change, but
I was not jumping up and down with excitement. Unfortunately, after seeing
the activity on the ISS digipeater in the past day or so since the
replacement VHF radio was put on 145.825 MHz, my worries have been

For many, the move to 437.550 MHz meant many stations that could easily
work 145.825 MHz would have to change. Whether it was a different antenna
for the 70cm band or dealing with Doppler with the 437.550 MHz frequency,
almost all of the unattended stations that had been present on the 145.825
MHz frequency were gone. If you wanted to use the ISS digipeater to work
other stations, this was a great opportunity. Many stations using
APRS-ready HTs and mobile transceivers were showing up, using a group of
memory channels to compensate for Doppler, and were making contacts. Some
fixed stations, including those already capable of satellite operating,
were also showing up. Even on the busier passes, the
437.550 MHz always seemed to be clear of the clutter from the unattended
stations that previously inhabited 145.825 MHz.

Fast forward to yesterday (Friday, 14 April). The ISS digipeater switched
to 145.825 MHz in time for afternoon/evening passes over Europe (around
1330-1400 UTC). Lots of stations showed up, based on looking at the
ariss.net web site. The same thing started to happen here in North
America, later in the day. The passes I worked last night were not bad,
but there were more stations on one pass that went over much of the
continental USA than I'd typically see on 437.550 MHz.

By midday today (1900 UTC), it seemed like many more stations were on the
frequency. I saw 11 other call signs on a pass just after that time this
afternoon. At best, there may have been 4 or 5 other operators at their
keyboards or keypads, looking to make contacts.
The others were just squawking away, not answering APRS messages sent to
them. By the time the ISS footprint was reaching the east coast, the
frequency was congested. Lots of position beacons were coming through, but
not much of anything else. This is not new; Clayton W5PFG wrote about this
about a year ago, here on the AMSAT-BB list:


For the two passes I worked this afternoon, around 1900 and 2035 UTC, I
made two QSOs on the earlier pass, and one on the later pass. A shame,
considering there were so many other call signs on the earlier pass, and
even some rare spots - stations in DM44 in northern Arizona and CM86 in
Santa Cruz CA were seen.

It is interesting that hams want to have their stations squawk on
145.825 MHz when nobody is at the keyboard. It could be doing it 24/7, no
matter if the ISS is in view or not. Would anyone think of setting up
their satellite station to automatically transmit their call sign and
location every 15/30/60 seconds to SO-50, unattended? I think not! That
could be a violation of the regulations, and would definitely be poor form
by that operator.

Bob Bruninga WB4APR has a couple of documents with recommendations for
beacon intervals when working the ISS digipeater. One mentioned a 5-minute
interval for unattended stations:


Another document recommends that unattended stations should be in "receive
ONLY mode." (emphasis is Bob's):


I agree with the latter. If your station is unattended, why have it
transmit at all?! It may be different for less-populated parts of the
world, where gateway stations may transmit and then receive their beacons
from the ISS, which will show up on ariss.net and other sites. For Europe,
and definitely North America, the gateways really don't need to transmit
if they are unattended. There should be activity on most passes, maybe
even late into the night, to know 145.825 MHz on the ISS is up and

Please don't misunderstand me... I think it is great for hams to set up
gateway stations listening on 145.825 MHz for the space-borne APRS
activity (ISS, NO-84, even NO-44 when it gets enough power to transmit
complete packets). But these stations, like other stations that aren't
operating as gateways yet transmit automatically, shouldn't contribute to
the congestion on the frequency.

I know I am in the minority on the ISS digipeater moving back to
145.825 MHz. Between the unattended stations clogging up the frequency and
some local interference I hear on 145.825 MHz around my house, having the
ISS on 437.550 MHz was fun! I worked it from home, and on some of my road
trips in the past 5+ months. Even for some of my last NPOTA activations at
the end of 2016. I'll continue to work the ISS digipeater, almost
exclusively with my APRS-ready HTs (TH-D72A, or TH-D74A), looking to make
QSOs by exchanging APRS messages with other stations. If you can work
packet from your station, and we are in the same footprints, I hope to
hear you (and see you on my screen) soon. Like W5PFG mentioned a year ago,
let's get more stations on 145.825 MHz making QSOs...


Twitter: @WD9EWK
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