[amsat-bb] ISS Digipeater is back! On UHF this time (437.550MHz)!

Patrick STODDARD (WD9EWK/VA7EWK) amsat-bb at wd9ewk.net
Wed Nov 2 23:13:24 UTC 2016


If you want to compare the new 70cm ISS packet setup with other satellites,
it is like how we receive SO-50 and transmit to AO-85 - but at the same
When receiving SO-50, the 70cm downlink frequency moves down. For AO-85, the
70cm uplink frequency moves up. For those using radios that can't be
by software like SatPC32, and as mentioned earlier in this thread, this can
be handled by a group of memory channels.

I posted a chart on how I programmed my TH-D74A to work 70cm ISS packet
to my Twitter feed last night. The same chart is below, but with the
additional information on the size and direction of the offset used
for each memory channel...

Channel 1: Receive on 437.560, transmit on 437.540 (offset of -20 kHz)
Channel 2: Receive on 437.555, transmit on 437.545 (offset of -10 kHz)
Channel 3: 437.550 simplex (receive and transmit are the same frequency)
Channel 4: Receive on 437.545, transmit on 437.555 (offset of +10 kHz)
Channel 5: Receive on 437.540, transmit on 437.560 (offset of +20 kHz)

For some radios, 4 of the 5 channels will have the receive and transmit
frequencies stored in the channels. With other radios, you will store
the receive frequency and the size and direction of the offset instead
of the actual transmit frequency.

I worked an ISS pass this morning using the 5-channel setup in my
TH-D74A, a western pass starting around 1320 UTC. There were times that
I had to switch between two channels, as the apparent uplink and downlink
frequencies were falling almost exactly between these channels when using
5 kHz tuning steps. My TH-D74A, like most non-Chinese ham HTs, doesn't allow
for 2.5 kHz tuning steps. I was able to get my position packets
retransmitted about 90 seconds after AOS, sooner than I normally would
when working ISS packet on 145.825 MHz when the station is to my
west. I saw two other stations this morning, KK6OTJ and AI6GS, both in
southern California. I was able to make a QSO with KK6OTJ using APRS
messages, and saw position packets from all 3 of us through most of the

Another thing about this morning's pass... with the frequency change,
and maybe also the need to adjust frequencies to compensate for Doppler,
there were no unattended beacons on the frequency! Other than the RS0ISS
ID beacons, I only saw stations where an operator was at the keyboard
or keypad during the pass. Now that was nice!


Twitter: @WD9EWK

On Wed, Nov 2, 2016 at 2:46 PM, mvivona--- via AMSAT-BB <amsat-bb at amsat.org>

> OK, now it makes sense. I had to draw some pictures to get it straight in
> my head. Thanks for explaining.
> I was attempting to compare it with SO-50, but since you TX on VHF it's
> not an issue.
> Cheers, Michael KC4ZVA

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