A nice thing about amateur radio is that the hobby covers so many things. Today, I’m interested in satellites. I’m getting my thoughts together on what information one needs to work them. I think the information I need includes:
- The time the satellite will rise above the horizon. This is called the acquisition of signal (AOS).
- The location or azimuth of where the satellite will come up over the horizon.
- The time the satellite will fall below the horizon. This is called the loss of acquisition of signal (LOS).
- The azimuth of where the satellite will fall below the horizon.
- The time of closest approach (TCA).
- The uplink frequency used to transmit to the satellite.
- The downlink frequency used to receive from the satellite.
- The peak elevation the satellite will reach.
There are many web sites and applications that can provide this information. I typically use Ham Radio Deluxe on a desktop computer and have a few mobile apps on my phone. These apps download satellite information, Kepler data, and present it in different ways to make life a little easier. Here is a text representation from Ham Radio Deluxe of FM satellites I monitor.
Satellite AOS LOS Duration Peak AZ Peak EL
AO-91 9/14/2019 14:41:08 14:54:14 00:13:06 269.6° 14.6° AO-85 9/14/2019 18:44:24 18:57:53 00:13:29 109.6° 18.3° SO-50 9/14/2019 20:17:54 20:29:29 00:11:35 42.6° 11.4° AO-85 9/14/2019 20:23:29 20:38:48 00:15:19 302.0° 50.6° SO-50 9/14/2019 21:57:33 22:12:01 00:14:28 92.0° 89.4° AO-92 9/14/2019 22:28:50 22:39:11 00:10:21 70.0° 16.7° AO-92 9/15/2019 00:01:55 00:13:00 00:11:05 264.0° 23.7° AO-91 9/15/2019 00:57:45 01:08:57 00:11:12 90.0° 13.9°
Figure one shows elevation graphics of the satellites. The higher the pass, the higher the higher the graph peak. In theory the higher passes should provide better signals.
Figure two shows the radar view. This graphically shows where the satellites will rise above the horizon – the acquisition of signal, the path the satellite will take, and where the satellite will fall below the horizon – the loss of signal.
The time of closest approach is the highest point of the pass and where Doppler shift should not be necessary. Graphically, this should be half the length of the pass shown in the radar view. These satellites operate on 2 and 70 centimeter frequencies. Although not significant on 2 meters, one does need to adjust the frequency due to Doppler shift on the 70 centimeter frequencies.
If you have the luxury of connecting your radio to your computer, software like Ham Radio Deluxe will adjust Doppler shift frequencies. Since my antenna is a handheld, I have to be outside to work satellites and therefore, I’ll need to adjust for Doppler shift manually. I’ll try to make this as painless as possible by putting a range of frequencies with 5KHz offsets in memories and change memories as the satellite passes. Here are the frequencies programmed in memories for satellite SO-50.
- Memory 1 – 436.805
- Memory 2 – 436.800
- Memory 3 – 436.795 – the downlink frequency -no Doppler shift.
- Memory 4 – 436.790
- Memory 5 – 436.785
As far as I can tell, Ham Radio Deluxe does not provide the frequencies for satellites. I usually get that information from web sites or mobile apps.
When I go outside, I’m going to figure out which way is North, either with a compass or use the one on my phone and look to the horizon where the acquisition of signal should be and make a mental note of a landmark and turn and do the same thing for where the loss of signal will be. From there I’ll estimate the peak elevation and visually trace the path the satellite will take. Hopefully, this will be enough to get me started. As the satellite actually arrives, I’ll open the squelch and point the antenna towards where the satellite should come up over the horizon and listen for changes and move the antenna and adjust the frequency as the satellite crosses the sky. At mid-point, the frequency on the 70cm band should match the satellites as Doppler shift isn’t necessary. Lastly, remember that these satellites spin and one needs to also twist the antenna if it isn’t circularly polarized. We’ll see how it goes.