Transponder and other settings for Radioskaf-B (ARISSAT-1)

Currently there is no info for the transponder and other downlinks of Radioscaf-B (ARISSAT-1)
in Gpredict. But fear not dear reader, help is down below :).

Just create the following in a file named 37772.trsp and copy it into your ~/.config/Gpredict/trsp folder

[ARISSat U/V Lin]
UP_LOW=435742000
UP_HIGH=435758000
DOWN_LOW=145922000
DOWN_HIGH=145938000
INVERT=true

[Digitalker/ SSTV FM]
DOWN_LOW=145950000

[Telemetry Mode v]
DOWN_LOW=145920000

[CW TLM Beacon BPSK-1000]
DOWN_LOW=145919000

[CW TLM Beacon BPSK-400]
DOWN_LOW=145939000

This gives you immediate access to the linear transponder, the FM voice messages and SSTV images

as well as the TLM beacons. I haven’t tested it yet completely, so feedback is welcome.

73 de Mike

Changing default transponder settings in Gpredict

Almost all satellite tracking software I tried so far never got the transponder settings for
doppler control right out of the box. There is the theory and then there’s reality. In reality
I still had to look for my downlink signal in order to find the right frequencies. Now one
thing that I like to live by is that when I have to repeat certain things over and over, I like
to automate them. Same goes for setting the correct up- and downlink frequencies when
operating linear satellites.
In the current version (1.3) of Gpredict, there is no editor to change settings for transponders,
so your favorite editor (vi I’m assuming 🙂 ) will be your friend here to add a new transponder
to the config file of the satellite.

Let’s do this for VO-52. First we need to get the catalogue number of the satellite as Gpredict
organizes it’s information based on that. If we click on the desired satellite and look at the
highlighted field, we get that piece of info.

Now that we know the number (in this case 28650 for VO-52) we can go look for the matching file
that Gpredict uses to store the information in. It’s located in ~/.config/Gpredict/trsp

Let’s look at the file itself and see it’s format:

mschulz@shack:~/.config/Gpredict/trsp> cat 28650.trsp

[Indian Beacon]
DOWN_LOW=145936000

[Indian U/V Lin]
UP_LOW=435220000
UP_HIGH=435280000
DOWN_LOW=145870000
DOWN_HIGH=145930000
INVERT=true

[Dutch Beacon CW]
DOWN_LOW=145860000

[Dutch U/V Lin]
UP_LOW=435225000
UP_HIGH=435275000
DOWN_LOW=145875000
DOWN_HIGH=145925000
INVERT=true

As you can see, it’s pretty straight forward. First we have a label for the transponder followed by the
values for up- and downlink frequencies and if it’s an inverting transponder. Based on that, all we have
to do is add a new section for our matching frequency pair to the end:

[New U/V Lin]
UP_LOW=435220000
UP_HIGH=435280000
DOWN_LOW=145873000
DOWN_HIGH=145930000
INVERT=true

Note that I only changed one side, in this case the downlink frequency to keep things simple. The way
I determined how to change it was also pretty easy. I just set my uplink frequency in the middle of the
passband where Gpredict would put it also. Then I tuned in my downlink signal and noted the difference
in frequency from the passband middle, which gave me the value by which I had to change the settings
in the config file. As you can see, the new setting is 2kHz lower than the original one which is roughly
where I want it to be to have to only fine tune my downlink signal.

Have fun tuning your Gpredict settings and see you on the birds.

73 Michael

Using your TS-2000 with Gpredict

One of the things that are key to having a pleasant experience working linear
transponders is software controlling your doppler shift. I’ve been a proponent
for manual tuning once when I was dismissing software control as something
for people who don’t know how. Well, let’s say I saw the light and leave it at that :).

Gpredict does a pretty good job but of course different than let’s say HRD which
I use when running Windows or MacDoppler on Mac OS.

In Gpredict you enable radio control by selecting the appropriate module in the drop
down menu on the right. Select your radio in the Settings portion of the window and
click on engage. On the left hand part of the window you can select your satellite and
the matching transponder (or beacon if you just want to track that) and click on Track.
Now when you click on the T button to tune the radio to the frequencies it never works
for me right out of the box to be spot on and I have to do some manual tuning.
While tuning manually, the Trace function on the radio needs to be off! Otherwise
you’ll be chasing your tail.
The way I do it is to leave the uplink signal where it is and then manually tune to find
my downling signal. Once that’s the case Gpredict keeps tracking both in sync and
you can work the satellite. So far so good one might think, but what if I want to change
frequencies? Clicking the L button links the two VFOs but unfortunately changes the
uplink frequency to what it thinks matches the downlink which is usually not correct.
The way I found a working solution for me was to first find my downlink, then turn on
the Trace function and on the linear satellites also the REV so that you track your
uplink frequency against (or in reverse) to your downlink frequency. Now I can tune
across the passband while keeping both frequencies close. It’s not a 100% match.
Once you’re at the desired frequency, you can then tweak the uplink to match the
downlink. Tuning the uplink VFO does not change the downlink, the other way around
both frequencies change.

While this sounds complicated at first, once you try it out it is pretty straight forward
and gives you the most control over where you want to be in the passband. After
tuning to the new frequency I turn the Trace function off in case I need to fine tune
the other station without changing my uplink.

This might work for other radios like FT-847 and IC-910H similar, I’m not familiar
with those so feedback is as always welcome.

73 Mike K5TRI

Fixing some issues in Gpredict

Update: after installing the new version, it can no longer engage with my TS-2000
via rigctld. Need to look into it as to what changed there. So for now it’s probably
better to stay on 1.3 if you’re using rig control.

In the past I had some issues with Gpredict when tracking a satellite and having
Gpredict control my TS-2000. Mike K2MTS reported a similar problem on the list
hosted on Sourceforge, that his FT-847 would flip-flop between uplink and downlink
frequency. I saw the same problem with Gpredict 1.3 on my TS-2000.
Alexandru OZ9AEC submitted a fix to SVN and I finally got around to check out the
new code and bring my version of Gpredict to 1.4svn which should solve that problem.