Rigs and Coax for Amateur Satellite Operation

Satellites

The various amateur satellites can be used for commuication if the proper antenna and rig is used. The first thing to understand is that some satellites orbit close to earth (referred to as Low Earth Orbit (LEOs)). Other satellites have their orbit carefully set so that their orbits exactly match the rotation of the earth. These satellites are called Geostationary satellites. These satellites are used by TeleVision Receive Only (TVRO) systems but not amateur satellites. Another type of satellite orbit is the eliptical orbit the swoops down close to earth and then swings far away. AO-10, AO-13 (Extinct) and AO-40 are this type.

Amateur satellites are intended for 2 way communications. Like FM repeaters, they receive on one frequency (band) - called the Uplink, and transmit on another frequency (band)- called the Downlink. Rigs designed for FM repeaters are usually half duplex, either transmitting or receiving at a time, but not both simultaneously. Rigs designed for amateur satellites operate in full duplex mode because they are often called upon to set the transmit frequency relative to the received signal.

Some satellites are designed as Telemetry repeaters; some are made for FM voice, and others are made for SSB and CWoperation. The FM LEO satellites, such as AO-27 and UO-14 (extinct) operate on a single 2M uplink frequency and a single powerful 70cm Downlink frequency. About 1/8 the world will being trying to use this one FM frequency for about 10 minutes. The strongest signal wins. By carefully timing when I transmitted I was able to work UO-14 using my handheld running 1 watt into a 1/4 wave whip. One time. Many mobiles have been able to briefly commuicate through UO-14 or AO-27.

The SSB and CW LEO satellites like FO-20 and FO-29 are one of the biggest operational challenges. The doppler effect is extreme and the entire pass only lasts 15 minutes or less.

The high orbiters AO-10 and AO-40 are comparatively easy, but offer special challenges themselves. AO-10 has a 435 MHz Uplink and a 145 MHz Downlink. It lost its battery backup and control computer years ago, so it only operates when orbiting in the sunlight, and is very weak. Large antennas with reversible circular polarization are the norm. Proper antenna aiming, doppler shift tracking, and polarization changing will be rewarded with a contact.

AO-40 is currently like AO-10 in many ways except that the receive fequency is at 2401 MHz, so your average rice box won't work directly. Typically a downconverter is used that converts 2401 MHz to 145 MHz.

RIG

Most AO-40 operators start off with one of the all mode VHF/UHF transceivers. You'll need 435 MHz (70CM) SSB or CW for transmit, and 145 MHz (2M) for receive after a 2401 MHz to 145 MHz downconverter. There are 4 front runners:

Yaesu FT-736R - Comes with 2M and 70CM capability. Claimed SSB power output is 25 watts on either band. Includes power supply. No longer made, but often found used for ~$500, up to $1000 if accessory modules for 220 MHz and/or 1200 MHz are included. Frequently found with 70 CM 100 W amp (& 2M 150 W amp) & power supply. Add another $500 to $700. Has a tendency to transmit into your downconverter which can blow the output stages in the downconverter.

Yaesu FT-847 - HF, 2M and 70CM capability. Claimed SSB power is 100 watts on HF, 50 watts on VHF & UHF. Price is ~$1300, not including a power supply-another $150. Probably the most popular rig on AO-40. For some strange reason, it has no VOX. I thought that was standard since 1954 on my Central Electronics 10A. A 1200 MHz module is not availble for this rig.

Kenwood TS-2000 - HF, 2M, and 70CM capability. Claimed SSB power is 100 watts on HF - 2M, 50 watts on 70CM. Price is ~$1800, not including a power supply-another $150. Can also be purchased with a 1200 MHz module or factory retrofitted for another $550 (recommended). Has more bells & whistles than any rig should be allowed to have, all reachable through obscure menu manipulations. It has a built in DSP that is quite useless on AO-40's white noise. Has no capability of powering line powered preamps, popular with the LEOs. Works great on AO-40, but a lemon on some satellites like AO-27 (45 over birdy right on the the AO-27 receive frequency.) Kenwood seems uninterested in correcting several known problems with this rig and has been offering $500 off on these turkeys. Operation on AO-40 is convenient and the cpomputer control port can be used for automatic doppler correction when receiving the beacon.

Icom 910H - 2M and 70CM capability. Claimed SSB power is 100W on 2M and 75W on 70CM. Current price is ~$1150, not including a power supply-another $150. Unlike the 847 and 2000 above, it does not include HF capability, so is not usable standalone for some the the satellites with 10M and 15M linkage. Several accessories are available such as a user addable 1200 MHz module for $500 (recommended) and antenna mounted preamps for the 3 bands (~$200 each), though the preamps do not have a very spectacular noise figure. ICOM also offers an expensive downconverter for 2401 MHz . It has programmable line powering of the preamps. In the interest of self support, there is no mention of what line powering means in terms of voltage, current, etc, but seems to be about 12 VDC. Also has plug in CW filters & a DSP module that actually removes some of the AO-40 white noise. Somewhat inconvenient operating AO-40, as the full duplex nature of satellite work requires constantly riding the AF gain, and the AF gain control is at the top of the front panel. On transmit the output indicator uses the S meter scale. Innovative. When asked how much power I'm running, I just say, "S7". When I first got my new Icom 910H, I was very upset to discover that there was no way to work the FM satellites in satellite mode. I called ICOM and got a real person in less than 5 minutes! However, though friendly, he was unfamiliar with satellites and has not returned the call to answer my questions. After a few hours twiddling the knobs, I discovered a way in non-satellite mode to work UO-14 and AO-27. Working AO-40 was a bit upsetting too, as the tuning dial went backwards compared to any other rig. Then I found that by turning off the SUB button, the tuning direction changes. The bottom line is - don't loose the Operator's Manual! It ain't much, pigeon English at best, but this is not a beginners rig! The directions tell how to work FO-20 and FO-29 (Japanese satellites). I guess the other amateur satellites don't count to ICOM. Click here to find out how to work US satellites with an ICOM 910H. My ICOM 10 watt 1200 MHz module actually puts out only about 6 watts. But with my 14' dish, I only run about 1/4 of a watt anyway.

Spectrum Analyzer

I recently picked up an ICOM PCR-1000 for about $300 which is a PC based receiver that tunes from Audio frequencies to 1300 MHz. I put a coaxial Tee in the 2 meter input line to the transceiver and feed the 145 MHz ouput from the downconverter to both the transceiver and the PCR-1000. I then downloaded some English spectrum analyzer shareware with a particularly obnoxious habit of putting on a "nag screen" every 10 minutes until you register it for $45. I can now monitor the AO-40 spectrum and see when and where new stations pop up. It usually shows Leila marching up and down the band, when nobody is on, bleeping away from the Middle beacon around 2401.320 to 2401.420! She does not do this below the beacon, so others and I have had enjoyable Leila free QSOs around 2401.300 MHz. KG6IAL has captured the Radar pulses running up to 20 db STRONGER than the beacon on his PCR-1000 .

The spectral picture from KG6IAL at the right shows the middle beacon (normally the strongest signal) at -110 db and a radar pulse going off the top beyond -100 db. The spikes above and below the radar pulse are two QSOs in progress.

Coax

Surprise, surprise, you need good coax at UHF and above frequencies.

The 2401 MHz downlink frequency usually goes into a downconverter mounted right at the dish. The output of the downconverter at 145 MHz is not so critical. I generally use RG-6 cable with a molded type F connector. The AIDC downconverters have excess gain, and a bit of loss is actually an advantage. But one thing to consider is that 145 MHz is also occupied by powerfull repeaters, and if the coax has marginal shielding you could have FM repeaters showing up in the middle of AO-40. The UEK-3000 itself does well at picking up these 145 MHz repeaters at my QTH. Some AO-40 hams use a DownEast preamp at the dish and then run the amplified 2401 MHz low loss coax into the shack where they locate the downconverter. Unfortunately the preamp easily desenses from the uplink signal but the downconverter is more stable since it avoids frequncy drift due to temperature extremes.

I use low loss AIRCOM coax on my 435 MHz uplink and 1/2" Andrew hardline on the 1269 MHz uplink. The hardline is too stiff for moving well with the dish, so I use flexible double copper shielded ECOFLEX 15 5/8" coax from SSB @ $2 a foot from the base of the 14's tower to the tri band patch feed. The overall loss on my uplink coax is about 3 db, meaning 1/2 of my uplink power is lost before it gets to the dish. But with 20 to 30 db of gain, I can afford 3 db loss. I recent got some 7/8" Andrew hardline to replace the uplink cables. I don't really need it but the price was right. Large diameter hardline shows up frequently at Denver Hamfests beause it was used on analog cell phone towers that have been replaced by the higher frequency digital cell phones. Many serious satellite operators use the thicker version of LMR coax to achieve low loss on their uplink.

Robert W0LMD