Saturday, May 11, 2013

Amateur Satellite Contacts

The thing that brought me in to Ham Radio in the beginning was satellite contacts. I was a student at a university building an amateur satellite. We operated on the Amateur Bands. In order to operate, one had to have an amateur license. While we were at it, one of the most common things we did was to talk to other amateur satellites, to practice tracking satellites in frequency and location. Thus began my first period to study to take the technician license exam.

So, the question quickly becomes, what do you need to talk on an Amateur Satellite? Most satellites are 2m/440 connections, so you need a transceiver that can work with both of those bands. In addition, you will need some sort of a directional antenna. A high end system might include an antenna that can be pointed in azimuth and elevation attached to a roof. Most satellites are actually set up so a modest handheld yagi antenna is sufficient, such as the Arrow Yagi Antenna, shown to the right. Note that it has more beams for the UHF (440) than the VHF (2m). This is because the gain is essentially based off of the length of the boon, but the elements need to be placed based on the wavelengths. Thus, the gain for each band is approximately the same in this case, despite the differing number of elements.

So, you have an antenna, and a dual band transceiver, now what? The next step is to figure out what satellite to talk to. The best place to find the status of Amateur Satellites is the AMSAT Satellite Status page. An alternative can be found at As of the writing of this blog, the only FM repeater satellite active is the SaudiSat SO-50. The uplink is 436.795, the downlink 145.850, and a PL Tone of 67.0Hz is required. More are in the works, and there are a few that do cross band SSB, but for now, this is the major bird.

Okay, so you know what satellite to talk to, now what? You need to know when it will pass overhead, and approximately when. Hands down, the best site is Heavens-above. Go there, get your location specified as best as you can, and see what you have in your area. I suggest you choose a pass at least 60 degrees for your first one (The elevation number), to give you plenty of time to make sure you can make the contact.

So, where will the satellite pass overhead? There are a couple of options here, but I'm inclined to use STK, as I also use the program at work. The key thing is to get a clue as to the direction it will pass, starting from the Acquisition of Signal (AOS, the point where the satellite crosses the horizon), to the LOS (Loss of Signal, where it leaves view). When the satellite should be in view, point your antenna in that direction.

Okay, so now you have a time, direction, and the frequency. Now what? Set up your station at least 5 minutes before predicted AOS. Make sure your location has good horizon visibility. Due to the Doppler affect, your transmit frequency will be lower to begin with, and higher at the end. The receive is the opposite, higher to begin with, and lower in the end. 440 has a doppler shift of 5-10KHz, 2m has one of 3 kHz. Bottom line is, you will need to adjust your 440 frequency as the satellite moves through the sky, if transmitting start low 5KHz, and slowly raise to 5Khz higher than the predicted frequency.

And that's really all there is to it. Good luck on making your first contact! For more information, see AMSAT's Working your First Satellite page.

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