FM satellites; an easy way to get into working the birds (1 Viewer)

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VO1ONE

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SatelliteGuys Pro
Aug 13, 2004
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Many hams have never tried working satellites before. Some try for the Space Shuttle SAREX missions, or maybe have worked MIR or the ISS at one time or another but haven't tried anything else. I know, until about a year ago, I was the same way. When I thought about operating satellite, the first things that came to mind were those multimode VHF/UHF radios which cost as much as HF radios and huge M2 beam arrays with az/el rotators. Being a poor university student, I figured that satellite would be like EME for me; one of those terribly expensive facets of amateur radio that I'd have to wait many years before I could afford to try it. Thankfully, I was wrong. While there are many who do spend thousands of dollars on a satellite station, you can get started with a complete setup for around $100 if you are handy enough to build a simple antenna and source some cheap radios. For most hams, you'll be able to get started for even cheaper, as most already have radios capable of working some satellites, the FM satellites. Suprised? I was!

Right now, there are 3 satellites which operate FM. You uplink to them on 2 meters, and they transmit back down on 70cm. There's SO-50, AO-27 and AO-51.

SO-50 is the hardest of the three to work. It doesn't transmit very much power (300mw I think?) so it's harder to hear than the others, and it doesn't transmit a carrier unless someone is uplinking to it. Plus, it has to be turned on by someone every 10 minutes. Uplink is on 145.85 MHz with a PL tone of 67Hz. To turn on the satellite, transmit for a couple of seconds with a PL of 74.4Hz. The satellite will NOT give you any confirmation that your command worked; you'll just have to check to see if you hear yourself when you transmit 67Hz. Downlink is on 436.795 +/- 10kHz for doppler.

AO-27 is easier than SO-50, but only operates voice mode for 6 minutes per pass. It starts off with packet for 20 seconds, then goes into voice mode for 6 minutes, then back to packet for 1 minute before shutting off. This is because the satellite is getting old and it doesn't have the energy to be on 24/7 anymore. AO-27 when in voice mode always transmits a carrier modulated with white noise. You can hear the difference and see it on the signal meter when you are picking it up. This makes it easier to aim at. It's also stronger than SO-50 so it's not difficult to receive. AO-27 also does not require PL to operate so people with really old radios won't have a problem working it. Uplink is same as SO-50 sans PL, 145.85. Downlink is also the same, 436.795 +/- 10kHz for doppler.

AO-51, also known simply as Echo, is the easiest to work of the three. It transmits the most power, and transmits a blank carrier when not in use. It's on 24/7 so no problems trying to squeeze in a million QSOs into 6 minutes of a 15 minute pass. However, AO-51 changes modes depending on what kind of feedback the control team gets. The default mode is FM with VHF uplink and UHF downlink, but they also do sideband up, PSK31, L band up and S band down. This satellite also runs packet on a separate frequency most of the time, too. The schedule and frequencies are posted at this link:
http://www.amsat.org/amsat-new/echo/ControlTeam.php

Most of the time, they are running uplink 145.92MHz with a PL of 67Hz and downlink at 435.3MHz +/- 10kHz for voice.

What do you need to work these sats? I use an arrow handheld antenna and two HT's. I have an old Radio Shack HTX-202 2 meter only radio I hadn't used in a couple of years. I had it hooked up on APRS for awhile as a low power tracker but satellite was a good reason to bring it back into good use as an uplink radio. I got a Yaesu VX-7R I use for the downlink, but you could do just as well with an HTX-404 or any other monoband 70cm radio. Don't use a scanner for a downlink. It might work but they usually lack the sensitivity needed that a real ham radio has in the 70cm band. Just looking at eBay completed auctions, you could get an HTX-202 AND an HTX-404 for about $80 total. I like using a different radio for the uplink and downlink because you can hear how well you're getting into the satellite; full duplex. Let's you make adjustments on the fly and see if you're getting QRMed or QRMing someone else. Some fancy new HT's have dual receive and can receive on 70cm when transmitting on 2. This is fine if you have an HT like this, BUT you'll need a duplexer to use an antenna with a seperate feed for 2m and 70cm like the arrow. Duplexers not required when you use two separate radios.

Antennas. The arrow handheld yagi is a small lightweight yagi antenna with 3 elements on 2 meters and 7 elements on 70cm. You don't have to buy one, you can construct one very easily for about $20 in parts, or cheaper. The most expensive part is the female BNC connectors! For the uplink, many just use a mobile 2m radio into a quarter wave ground plane. Not a lot of power is needed, 10 watts will do. Then all you need is a good gain directional antenna for the downlink. If you're using the arrow or similar, 1 watt works great for me most of the time, or you can pump it up to 2.5 or 5 or whatever your handhelds got and it will work. Got a 70cm beam already but don't want to walk around outside with it looking silly? You can hear low elevation passes with it even without an az/el rotator. Just use your omni on 2m with some power to transmit into it. You get the best DX on these low elevation passes. On high elevation passes, people have been able to work AO-51 with a quarter wave rubber duck outside positioning the antenna just right over a car hood as a reflector! Dualband HT and a quarter wave duck, no additional equipment needed!

The Arrow antenna is a great antenna. I worked Estonia, Italy, Sweden, Puerto Rico, California, Mexico, and many more with this antenna on passes as low as 2 degrees and down to the horizon at a good location.

http://www.arrowantennas.com/146-437.html

However, it is $73 and you can build the exact same thing yourself easily. Want to build one? Take a look here:

http://xe1mex.gq.nu/antenas/yagi.html

Now that you've got the equipment, all you need now is software to track the satellites. Try Orbitron, it's free! http://www.stoff.pl/

So, you've got all the equipment, and your tracking software of choice says a great 87 degree pass on AO-51 is heading your way! What do you do? If your doing the handheld method, find a clear area to stand where houses and large trees won't be in the directon of the satellite at any point during the pass. Remember when I said the downlink frequency was 435.3 +/- 10kHz? This is because of doppler shift. The satellite is moving so fast that the frequency you will receive it at will change as much as 20kHz during the pass! FM does make it a bit easier, though. Due to the capture effect, you don't have to change frequency all that much. With sideband, you're constantly turning the knob. On FM, you turn the knob 4 times. Set your radio's tuning step to as low as it will go. For most, this will be 5kHz, and this is perfect. Start off at 435.310 and turn your squelch all the way down. If you're using two radios, use a pair of headphones so you don't get feedback. I use a mono to stereo adapter with my HT so sound comes out of both headphones, and they're the muff type so not too much sound escapes. Point your antenna towards the horizon in the general direction of where the satellite is supposed to be. Rotate the antenna so that you're checking both polarizations. Soon you will hear the blank carrier (or someone talking!) of AO-51. DON'T transmit to the satellite until you can hear it! The satellites can hear you a lot better than you can hear it. Many times there could be a QSO in progress and someone who can't hear the satellite yet throws a carrier over the QSO without even knowing it. Once you've got a decent signal on the downlink, go ahead and transmit up to it on 145.92. Make sure your PL is on at 67Hz. The doppler on 2 meters is a lot less than what it is on 70cm. It's only about 3kHz but thanks to the capture effect of FM, transmitting on 145.92 the whole pass is close enough. You should be able to hear yourself through the satellite with a full duplex setup. This will allow you to fine tune your aiming and twisting of the beam. I like to use only 1 watt. When I use something like 5 watts, it starts to slightly desense my receive on 70cm but YMMV! Make some contacts! As the satellite gets closer, you will hear that it sounds like its getting distorted as if it is off frequency. This tells you it is time to tune down to 435.305. When it is nearly straight overhead, you'll tune to 435.3. As it's heading away from you, you go down 5kHz more to 435.295 and when it's almost gone you'll be tuned to 435.290. Now if you have a pass that's only a max of say 10 degrees elevation, you might start off at 435.305 rather than 435.310 so take that into consideration when you're listening for the sat to come above the horizon.

The FM low earth orbiting sats are great! You can work in excess of 3,000 miles with little HT's and a handheld antenna. You can get a VUCC award with these things quite easy if you QSL your contacts. Speaking of which, know your grid square. These are exchanged on every satellite QSO. If you don't know, it's probably on QRZ.com. Hope to hear you all on the birds real soon!

I know, I wrote this kind of quickly since the YL wants to go out, so if anyone needs anything clarified, let me know and I'll answer your questions to the best of my ability.

73,
Mark VO1ONE
 
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zaxxon2000

SatelliteGuys Family
Mar 13, 2004
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Excellent

Excellent post. I just got my 1st license and am going to try this. Thanks for taking the time to post the information.
 

VO1ONE

Thread Starter
SatelliteGuys Pro
Aug 13, 2004
177
6
Congratulations on getting your licence! Satellites are a great thing to get into for new hams and long time hams alike. For me, it was just another facet of this great hobby that brings me more enjoyment, in addition to the many things I already do with it.

Another nice thing about satellites for new hams is that it doesn't require a high level licence to get on. You can have a no-code technician licence in the states and still talk to someone thousands of miles away. Now I'd never not encourage someone to not upgrade, but this allows someone with a tech licence to get more out of this hobby and probably at least partially with equipment they already have.

Satellites, you don't have to worry about band conditions too much. Your sat tracking program tells you exactly when you'll hear the satellite to the second, you get 15 minutes to make lots of contacts and then you find yourself getting back on the computer figuring out how long it's going to be before another satellite is over the horizon for you! You hardly ever have to call CQ on an FM sat. Always a lot of people. One of these days, I'll save up to get some sideband gear for VHF/UHF. That'll open up several more birds for me. The nice thing about sideband birds is that several people can have QSO's on the satellite at once. Some of the passes on the FM birds are so busy the QSO's are almost contest style - callsign, name, grid, 73! On sideband, you can spend the whole pass rag chewing since everyone else can find their own spot on the satellite to use. Sideband birds take a bandwidth of say 50kHz on 70cm, and any signal that can fit into that bandwidth gets spit back down in the same 50kHz swath but shifted onto 2 meters. You can use the same simple directional antennas that you use for the FM birds, but radios are a bit more expensive. You can get one of those old Icom shoulder strap radios that transmit 5w on eBay for around $100 each.

Oh, I forgot to mention about doppler on my original post. I think I'll edit it now!

73,
Mark VO1ONE
 

VO1ONE

Thread Starter
SatelliteGuys Pro
Aug 13, 2004
177
6
OoTLink said:
totally awesome post :) You got me interested.

That's good to hear! It's suprising how many hams haven't tried working some voice sats. It's not that they're not interested, but most think that it's more complicated than it really is, where most of the time they already have everything you need to get on, maybe minus the antenna. It's nice to be able to do something else with a dual band HT, and it gives no-coders an opportunity to make contacts several thousand miles away without the use of echolink or IRLP or similar. The sound quality of course is a million times better than sideband, too, and a lot more reliable conditions-wise. It sounds like you're just talking on a repeater the next town over, not to some spacecraft a thousand miles away.

Anyways, give it a try. Even if you're not licenced you could still listen if you have a nice, sensitive scanner or a motorola business band uhf radio programmed to the right frequencies, or of course a ham radio. I'm thinking about building some of those XE1MEX Arrow clones myself and selling them to hams here locally to get more of us on the satellites. You don't need to be a member of AMSAT or anything else to use the satellites. Of course if you find a lot of enjoyment in using the satellites you might want to consider joining to help continue funding an organization which is responsible for building and launching a lot of these satellites. They plan on building and launching a HEO (high Earth orbiting) satellite soon which will allow for much longer passes and contacts of even greater distances, but such an orbit is more expensive to achieve than a low Earth orbit. Here's the page about P3E:
http://www.amsat.org/amsat-new/express/

73,
Mark VO1ONE
 
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