< Back to main page

N5DUX's Satellite Guide - FM

N5DUX operating AO-91 from ARRL HQ
in Newington, CT in 2019
Okay - so you're ready to get on the air with satellites! FM satellites are the beginner-friendly place to go for making satellite contacts. There's a large number of hams on these satellites which means you've got the ability to hear hams from all over the hemisphere.
I went over the equipment needs on the main page, but all you need at a minimum is an HT, a directional antenna, and (optionally) a voice-recorder. You'll also need some way to determine which satellite is passing overhead at your location, though there are a few different ways to determine that. (See the main page for details there, too).

FM Operation

Once again, if you're just getting started start with FM satellites first. Not only will you likely have more success with FM, you'll also create less newbie-induced QRM for others on the linear sats. :)
As always, listen first. With that, I mean if you have a directional antenna try tuning and tracking a satellite before fussing with transmitting to it. Just hearing the satellite is half the challenge. And starting out, hearing the satellite is the challenge! So let's start there. Let's first look at how to find the satellite. Great! So you've got the equipment and you've got a tracking app. The first area to explore is FM satellites. These are much easier to work and are known as "easy-sats" for this reason.


The absolute easiest "bird" to hear is the International Space Station. The radio on board the ISS is much more powerful than the other amateur satellites. Plus, if you're lucky you'll be able to see the ISS as you hear it! (a real treat) Depending on which mode the ISS is in, you may be able to hear the astronauts/cosmonauts speaking to school kids, speaking to ham radio operators (very rare indeed), SSTV images being transmitted, APRS packets being "digipeated" (digitally repeated), or even the FM voice repeater. To tune into the downlink of the ISS, you need to know which mode it's in.
If it happens to be a time when the ISS is transmitting SSTV images (done to commemorate certain space/technological milestones), the downlink frequency is likely to be 145.800.
Decoding SSTV images from the ISS
is not too complicated.
If the astronauts are speaking to a school or hams back on earth, the frequency is 145.800 also.
If the ISS is in APRS mode, the frequency will be 145.825.
If the ISS is in FM repeater mode, the frequency will be 437.800.
The trick for tuning the ISS is actually just getting your antenna (any antenna!) in the general direction of the ISS. Even a "rubber duck" antenna will work when tuning the ISS. Just remember the long side of the antenna is the direction the antenna is listening. If you know where the ISS is as it's passing overhead, tilt the antenna so the broadside of the antenna is "aimed" at the arc of the ISS. Let's assume the ISS is in SSTV mode. You need to set your HT to 145.800. To decode SSTV images, download an SSTV app like this one from Black Cat Systems. Set the app to decode PD120 and hold your phone's mic near your radio's speaker. With any luck, the image should start streaming into your phone 1 line at a time.

FM satellites

There are a few FM satellites operable and in orbit, but there are not many. SO-50, AO-91, and PO-101 are the 3 active FM satellites as of this writing.
The scarcity of FM satellites and the ease of working them means they are very busy on most every pass. Years ago I had one extremely rare QSO with a ham in Indiana. I was living in NE Texas at the time and it was very late at night (after midnight) and it was just me and him for the entire pass. We would pause and listen for others, but it was just us. It's usually so busy on the FM birds that it's hard to make more than 1 or 2 contacts on a single pass.

Tuning an FM sat

SaudiSat 1C, aka SO-50
(courtesy of AMSAT)
Pick your target. Let's use SO-50 as our example. It's probably the easiest of the active FM satellites in my opinion.
The downlink frequency for SO-50 is 436.795 MHz. So we'll set the receive frequency to 436.795.
Now, switch over to the other VFO and set that one to 145.850. That's the uplink frequency for SO-50.
While on the transmit VFO, enable the PL Tone, and set it to 67.0Hz.
With both VFOs setup, however you do it on your radio, enable "split" operation so that you receive with one VFO and transmit via the other. This will allow you to transmit on VHF while listening to UHF.
Now, click back over to your receive VFO (the one tunes to 436.795), and grab your antenna. I usually step outside and find some shade if it's hot or someplace a little out of the wind if it's not. I usually wait until I'm outside to attach the 2m elements of my Arrow antenna because it can be a little unwieldy getting it out the door otherwise.
Before the satellite AOS time, I open my squelch fully and turn up the volume to a reasonably loud volume. I do this because A) the signals you'll be hearing are coming in somewhat faintly and may not break squelch otherwise and B) because I need to hear those faint signals clearly. Headphones help, but we're trying to do this with the minimum of equipment. If you have a couple of minutes before AOS, go ahead and turn off the radio for a bit.

Visualizing the pass

Take note of which direction north is. I usually look for a landmark or tree to mark north. Refer to your satellite tracking app or jotted-down notes to remember the direction of where the satellite will come up off the horizon. Find a landmark for that direction.
Next, refer to your satellite tracker to see where maximum altitude will be, is there a landmark in that direction? What's the maximum altitude? Can you visualize how high up that is? As mentioned in the tracking page, you know that 90° is straight up, so 45° is half that. A little below that is 30° and a little above is 60°. With just that rough, rudimentary elevation estimate you'll be able to find the bird with no problem.
The last piece of the puzzle is to identify where LOS will occur. Any landmarks over there? So there you have it. That's the arc of the pass, you can see where it'll start, where "max" will be, and where it'll fade toward. The only other "gotcha" in that arc is to take note of any obstructions like tall buildings, billboards, water towers, or thick tree cover; those can block your reception. Thin radio towers, a single tree or two, or even telephone poles shouldn't have a noticable effect.
If you're fancy and have a digital voice recorder, go ahead and record the time and day and which satellite you're recording. (Remember, this one is Saudisat-1C and today is June 13.) So I might say "SaudiSat 1C, June 13th, 11:17am..." then hit pause on the recording.
Now, attach your antenna (you did get the right adapter if you don't have a female BNC on your radio, right?). Turn on the radio and dial the frequency up about 15kHz to 436.810 or so. Practice jumping down and back in 5kHz steps.
When the satellite comes up off the horizon, it'll be shifted up in frequency because it's coming at you (quite quickly, about 17,000mph±). The Doppler Effect makes the frequency appear shifted higher when coming at you and lowers when moving away from you. When it reaches max elevation it'll be "on frequency" (436.795 with no shift) and by the time you lose signal it'll appear to have dropped in frequency down to about 436.780.

The pass

At the time of AOS, unpause your recording (if you have one) and begin moving the antenna back at forth slowly in the direction of the AOS (point it at that landmark you noted earlier). Slowly twist the antenna too. Sometimes the antenna polarization can help hear the signal. Also jog the receive frequency back and forth 5kHz. (Try .810, try .805)
Remember too that AOS is not an exact, on-the-nose time. Sometimes it is, but sometimes there's a little delay in when you'll hear it. Sometimes, if you're up high like a mountain peak, you may actually hear it before the calculated AOS. Play with each of the variables: antenna direction, antenna polarization, frequency. At a magic moment you'll hear a voice come through the static. You got it!
As mentioned earlier FM satellites are very busy places --- I'm not sure what's busier an FM pass on any given weekend afternoon or 20m/40m on Field Day. It's a toss up. You'll almost certainly hear other stations making contacts as it comes off the horizon and climbs during your pass. You'll notice the QSOs are going very quick. On FM satellites, the QSO is nothing more than the callsign and their gridsquare. Boom, boom. The FM birds are often so busy that operators are "stepping on" one another to make contacts.
Even though your radio is setup to transmit, just listen for a pass or two. Get a feel for tracking the satellite. As the signal gets "scratchy" as it climbs, remember to drop your receive frequency. About halfway between AOS and maximum elevation you should be at 436.800. As it approaches or gets to max elevation, you should be right on 436.795. As it gets scratchy again, continue dropping in frequency to .790, then to .785.
Also, it should go without saying to move your antenna along with the satellite. Keep it pointed at the satellite as it traverses the sky above you through that arc you visualized before the pass. Continue twisting the antenna to find the best signal. When it's strong, turn the antenna and you should notice it fade noticably. That's why antenna polarization matters. It truly can mean the difference between hearing the satellite or not!
At the end of the pass, I usually state the time and stop the recording.

After the pass

You did it! You just tracked your first satellite! If you made a recording, head back inside to replay the recording. Write out the callsigns you heard and their gridsquares. Sure you didn't work them this time, but it's good practice to see just how far your little HT can get with only 5W. Locate those gridsquares on a gridsquare map. It's pretty impressive.

Working the satellite

Maidenhead Gridsquare Map
(courtesy of Icom)
So, you've listened to a couple passes and you're ready to speak up. Great! It all goes the exact same way as listening except you're going to throw out your call. When someone comes back to you, they may acknowledge your call or may not - it kinda depends how busy it is that pass. It's almost always busy - especially on weekends and holidays during pleasant weather. Evening passes are usually more busy that afternoon passes.
When the other station responds to you, they'll give their callsign in phonetics and their Maidenhead gridsquare. Be sure you know your gridsquare before transmitting! Saying "Ogema, Wisconsin" isn't what other ops want to hear. It's quicker and easier to say "Echo November 4 5" (EN45).
Keep your short-term memory sharp. Don't worry about remembering everyone you've worked, that's what the voice recorder is for! When you finish, you can go back inside and listen to the recording, write down the callsigns and gridsquares and enter it into your log. (most satellite ops are using Logbook of The World.)
Once you've logged the stations you worked from that pass, find when the next pass is coming and repeat the process.


Once you've been on the air for a bit, you may be wondering "What now?".
That's where the "thrill of the hunt" comes in through the various Awards you can achieve via satellite.
There are several satellite awards you can earn such as Worked All States, VUCC, and even the grandaddy of them all: AMSAT Gridmaster. Are you up for it?