AO-40

There are many types of satellites. Geosyncronous broadcast satellites are the best known. These satellites, often costing billions of $, orbit 22,000 miles up at the same rate as the Earth rotates and so they appear to be standing still. Another type of satellite orbits rather close to Earth and this type is called a Low Earth Orbitting or LEO satellite. Finally, the AO-40 type is one that orbits high like the geosyncrous satellites, but is not geostationary, which provides sporadic coverage to Hams all over the world.

Operating on a Ham satellite is much different than on a HF or VHF band. HF and VHF operation is almost always half-duplex, meaning that you are either transmitting or receiving at any given moment, but not simultaneously. Ham Satellite operation is Full Duplex, more like a telephone in which you can simultaneously transmit and receive. This requires either a special rig or a separate conventional transmitter and receiver. Remember when you tried to make a telephone call and you got this terible echo to your voice. This happens with the amateur satellites, so you will be constantly riding the AF gain on the receiver. Full duplex is required because, with Doppler and other effects, you want to be able to tune in your own signal. That's where any station calling you for a contact will appear.

Some of the amateur LEO satellites like UO-14 and AO-27 are single frequency satellites, generally FM, like an FM repeater. Your transmitter sends a signal to the satellite on one frequency and the satellite translates your detected audio to another single FM frequency on another band. It is a case of sharing a single repeater channel with 1000's of amateurs at the same time...It makes CB channel sharing look kinder, gentler. The advantage of this design that it concentrates all of the satellite's transmit power on a single frequency. The disadvantage is that only the strongest station makes it through. Success for a low powered station belongs to the sneaky. There are not many hams North of my QTH in Colorado. I worked UO-14 one day with my 1 watt Handie-Talkie & a 1/4 wave whip, standing outside my basement door, by waiting for a descending pass come over the North pole and Canada. Just as the satellite was in view over Colorado I made a 15 second contact with the lone Canadian on the satellite. A few minutes later, the whole USA could work the satellite, and I was at the bottom of the heap.

Other LEO satellites, such as FO-20 and FO-29, are operated over a band of frequencies. You select a frequency within this band for your uplink and the frequency is linearly transposed to a downlink band of frequencies. The advantage of this design is that several dozen stations can operate simultaneously. The disadvantage is that the satellite's power is spread out over all the transmissions, making the output signal much weaker. Because the orbit is low, your signal is generally strong, and a good satellite tracking system gives you a good strong contact, lasting about 15 minutes max. Occasionally someone gets on satellites like this with very high power, and the result is he hogs all the satellite transmitting power, killing all the other QSOs.

AO-40 is a satellite that was launched November, 2000. Right now, it is orbiting around the equator between 700 miles to 38,000 miles up. When it is 30,000 miles up or more, about half the world can communicate through it.

Exactly which half changes every day, ~repeating on a 4 day cycle, so Hams get some satellite tracking program for their home computer. The program tells where the AO-40 satellite will be at any given time and can even provide automatic rotator control. These tracking programs also work on the other amateur and commercial satellites and the orbiting space station.

I started off using a 3' barbecue grill dish mounted on top of a 50' tower between my other satellite yagis. Because I was interested in getting the best picture possible from SSTV satellite contacts, I modified an old 10' TVRO dish to pick up the 2401 MHz signal coming down from AO-40. I eventually replaced the barbecue grill dish with a larger PrimeStar dish with a 5 1/2 turn helix feed, and in the Fall of 2002, I added a 14' fiberglass Dish with a Tri-band circular patch feed..

Many people are using a 3' barbecue grill dish which which has become the rubber ducky of AO-40. BBQs pick up the rather strong beacon well, especially when the satellite 's propagation is most favorable, but most now agree that it is just not a serious receive antenna. The PrimeStar dish has over twice the area and is right circular polarized like AO-40 instead of linear polarized like the barbecue grill dish's feed system. The result is that the PrimeStar beats the BBQ by 4 db due to its larger size and a solid reflector surface, and the right circular polarization beats the BBQ's linear polarization by another 3 db. The BBQ grill dish cost $130; the PrimeStar dish was free; given to me by K2LCT. It was easy to tell the BBQ users on Field Day. They couldn't hear anybody (including themselves) and call for continual repeats of call, name, grid, etc.

The 10' dish has 78 sq. feet of surface, whereas the PrimeStar has about 8 sq. feet of surface. This tenfold increase in surface area provides 10 db more signal, so the net difference from the PrimeStar to the 10' dish is a 10 db gain in favor of the 10' dish. When signals are very strong it doesn't make that much difference. But most of the time, the satellite is not at its best and the 10' dish really makes a big difference. My latest addition, the 14' dish is 3 db stronger than the 10' dish because it has twice as much area.

My house and a forest full of pine attenuators block my 10' dish from receiving AO-40 when it is East of 145 degrees azimuth (European passes) so I generally use the 14' as my standard AO-40 antenna now. The 14' dish is mounted high so that it sees over the top of my house but some distant trees block it from seeing below about 4 degrees in elevation. The PrimeStar is on the top of a 50' tower, so it sees over these trees but not some distant 14,000' mountains (I live on a 9000' altitude mountaintop in Colorado) which sets the minimum elevation view at 2 degrees. The bottom line to all this is that with a standard barefoot all mode transceiver I can work anyone from Western Russia, Europe & Africa through the US and South America to Australia, Eastern Russia, & Indonesia anytime both of us are able to see AO-40.

How I Work AO-40

AO-40 carries several receivers and transmitters, but some space accidents have crippled several of them. Now the mode of operating AO-40 requires a way to send a 435 MHz or 1269 MHz SSB (LSB), or CW signal to a moving, non-geostationary, satellite, and a way to receive a 2401 MHz SSB (USB) or CW signal. The desired mode is full duplex, in which you hear your own signal returning on the receive frequency. Most people on AO-40 use 435 MHz and SSB, listening on 2401 MHz, and that is what I use during poor conditions. Most of the time I now use the 1269 MHz uplink and listen on 2401 MHz.

You might think that the signal would be blasting away when it is 700 miles up and weak as sin when 36,000 miles away. Not so. Another factor enters in called Squint. The antennas on AO-40 are not omnidirectional; they have a favored pointing angle just like your 20M beam antenna. If the satellite is pointing its antenna sideways when 700 miles up, and right at you when 38,000 miles up, you won't hear it right overhead and close, but you will be able to work almost 1/2 the world on 10 watts when it gets 38,000 miles up. When the squint gets over 25 degrees, most stations don't bother with AO-40, as the signal will be quite weak. The squint is calculated from 2 parameters published by AMSAT called Alon and Alat which you need to load into your tracking program.

The next level of difficulty is the satellite's operating schedule. AO-40 may be right over your QTH, but turned off! AMSAT controls its operating schedule which is frequently changed with minimal notice. The schedule is based on the satellite's position in its orbit. A term called "Mean Anomaly" (MA) is defined as a value from 0 to 255 (like 8 bit binary) where 0 is the lowest point in the elliptical orbit, and 128 is the highest point, and then going back through 255 to start over at 0 for the next orbit. Sometimes, the orbit and the sun and your QTH are not in a favorable alignment. Since the satellite needs the sun for its solar arrays, the sun get preferential treatment. So AMSAT has set a schedule when the best compromise, including Squint, is possible. Currently (7/4/03) AO-40 is turned on for 2 way amateur operation from MA 30 to MA 220. Usually nobody shows up until the lower squint levels.

I use the software program NOVA to find out exactly where AO-40 is. Nova utilizes mathematical formulas, called Keplers - Keps for short, your geographical coordinates, and your computer's clock, to calculate exactly where the satellite is in relation to your QTH. If everything isn't entered correctly, you'll never find it by yourself! The latest Alon and Alat numbers for AO-40 are also entered. I also tell NOVA that I am only interested in the portion of orbital time between MA 30 and MA 220, and when the squint is < 25, and visible from my QTH in Colorado. NOVA has a utility routine that will print out a schedule for my QTH, so I set it to analyze the next 10 days. I keep this schedule on my operating desk; it rules my life on AO-40. For instance, I saw that the squint was getting down below 1 degree Friday 2/15/02 at 10:50 AM with the satellite over the Pacific Ocean, the footprint covering an area from Nova Scotia to New Zealand, so I knew it would be hot. It was. The satellite had all kinds of activity for the occasion. I worked stations from Montreal to New Zealand, using 5 watts of SSB to my 10' dish.

When the satellite pass starts, I start up NOVA on my computer. It will tell me where to point my antennas. My VHF & UHF yagis and a PrimeStar 40" x 30" dish with a 5 1/2 turn helix feed are on a 50' tower next to the house with a Yaesu G-5500 azimuth and elevation rotor turning them. I designed a unit last year, called a Satellite Tracker Jr. , which takes NOVA's COM port output and the analog position outputs of my Yaesu G-5500 rotator's control box . I activate tracking, and the yagis and PrimeStar dish are now locked onto AO-40's moving position. I also turn the 10' & 14' dishes automatically to AO-40's azimuth and elevation bearings. I use a large dish system I designed called Satellite Tracker Sr., described later on this webpage.

An article by K6LG in the July , 2003 issue of QST told how to use a 10' TVRO dish without changing its polar mount. This is certainly a nice idea, but unfortunately the tracking programs can't be used to automate the tracking, making manual operation the only option. The bigger the dish the narrower the beamwidth (a 10' dish on 2401 MH is about 2.8 degrees wide; the 14' is just over 2 degrees), so use is more difficult and you will already have your hands full tuning the rig for Doppler shift. Before I automated the tracking, I was usually moving the 10' dish in azimuth every other transmission.

Since AO-40 is over the equator, my antennas never point North of 90 degrees or 270 degrees azimuth. If the satellite is over the Atlantic, it will be somewhere between 90 degrees and about 135 degrees azimuth. My 10' dish is blocked on this pass, so last year I used the PrimeStar dish on the Yaesu G-5500 rotator for this European pass, along with the 435 MHz 40 element KLM cross yagi, which sees over the house and trees. When the satellite is over S. America or the Pacific, I have a clear shot with the 10' dish, so I will switch to the tri band patch (2401 MHz, 1269 MHz, and 435 MHz) on the 10' dish and get a much better signal. The PrimeStar dish is attached to an SSB UEK-3000 downconverter and 10' dish's 2401 MHz patch is connected to a surplus AIDC 3731 downconverter. The output signals at 145 MHz are brought into the hamshack on RG-9913 cables to a switchbox and into my ICOM 910H's 2 meter coaxial connector. The 14' dish has a better sight picture so is now generally the only dish used for an AO-40 satellite pass.

AO-40 has a loud beacon signal called the Middle Beacon (MB), about 10 db stronger than any other signal, somewhere around 2401.330 MHz. I say "around" because the doppler shift will move this apparent frequency around a bit, say + or - 25 KHz. When NOVA tells me that the satellite is turned on, and with my dishes and yagis pointed where NOVA tells me the satellite is, I just tune around 145.330 MHz on my rig until I hear the distinctive screech of the beacon signal sending telemetry.

If you can't hear this beacon, go no further! A very useful tool is a signal source that puts out a detectable known signal on 2.4 GHz for times when AO-40 is not up. I recently built a small signal source consisting of a 50 MHz TTL oscillator in a small die cast box with female type N chassis connector and a 4.8 volt rechargeable nicad battery for power. The TTL oscillator's case is fastened to the die cast box with heat sink grease so the oscillator will be more stable. I made a several different 2.4 GHz antennas for testing antennas' and feed systems' polarities.

Now this AO-40 beacon is not like tuning in a strong HF signal, It's much weaker, and at 17,500 MPH, it's definitely a moving target! My 10' dish has a 2.8 degree beamwidth at 2401 MHz, but even 10 degrees off, I can faintly hear the beacon. I have the 2M preamplifier in the rig on, and start moving the dish in Azimuth, peaking the S meter reading. After reaching an Azimuth peak then I do the same thing for Elevation. A few iterations and I have it as loud as it will get. At least for 5 minutes or so. Once over 20 degrees high in elevation, most of your corrections will be moving the satellite slightly to the West, unless it is in retrograde, in which case a slight correction to the East is needed. An occasional up or down elevation nudge will also keep the signal peaked. Just looking at the direction the displayed bearings on NOVA are going lets you manually correct the bearings in the proper direction. But you will more than have your hands full with basic satellite communications and doppler correcting so that I why I designed and use automated trackers.

Once peaked on the beacon, you can venture out to look for stations using the satellite especially if the squint is <10 degrees. SSB signals will be found from about 5 KHz to 70 KHz above the beacon. CW signals are generally below the beacon, but some lonely spirits on CW seem to like to nuzzle up to the voice stations and call CQ. SSTV operation is somewhat rare, but is generally found around 2401.350 MHz in the USA and 2401.370 Mhz up in Japan.

The most obvious thing you will find is that you are wearing out your tuning dial! The doppler shift from this satellite's movement will cause the received frequency to steadily cruise upward. Most stations just go with the cruise. Another reason is the downconverters themselves, while crystal controlled, are not all that stable, and may cruise down or up in frequency compounding the dial tuning problem. But it is nowhere as bad as the Low Earth Orbiting satellites (LEOs).

At some point you will get the urge to abandon your SWL habits and join the fun. Most likely you will have your rice box connected to a large yagi that works OK on 435 MHz. The trick is setting the transmit frequency.

AO-40 is operated full duplex like all the other SSB satellites. You tune the transmitter so that you can hear yourself. Once you hear yourself, you lock the transmit and receive frequency together so that when you tune in a station, your transmitter is on his (her) frequency. AO-40 requires a "Reverse" split lock - as the receive frequency goes up, the transmit frequency needs to go down.

Now the BIG QUESTION. I hear the beacon, where do I set the transmit frequency????     It is amazingly simple! With the Beacon tuned in at a medium tone range, set your transmit frequency to 435.666 MHz. Now reverse lock the rig's receive and transmit vfos together.

If you want to do battle with the gigantic, try the Mode L uplinks. AO-40 has two receivers on the L band listening for 1268 Mhz and 1269 Mhz, called L2 and L1 appropriately. The L2 receiver in AO-40 is about 6 db weaker than the L1 receiver, so plan to run 4 times more power if using L2. Now the BIG L band QUESTION. I hear the beacon, where do I set the transmit frequency????  It is also amazingly simple! With the Beacon tuned in at a medium screech, for L1 set your transmit frequency to 1269.388 MHz. For L2, set your transmit frequency to 1268.456. MHz. Now reverse lock the rig's receive and transmit vfos together.

For crying out loud, don't hit the transmit PTT yet! You may QRM the telemetry beacon, even less popular than calling CQ on top of the W1AW code practice frequency. With the frequencies locked, tune way up towards the top end of the satellite's passband where nobody operates. I usually tune up to 2401.400 which reads out on my rig as 145.400 MHz. Unlock your vfos and start saying "Hello, this is W0XYZ" or, if you are a Mathematician, "Hello 1, 2 , 3......". As you talk, tune your RECEIVER VFO to find yourself. If you set things as I described perfectly then you should be within a couple of KHz away. That first return will be a moment to cherish forever. Don't be a LID, setting your receiver vfo in the middle of the SSB transmissions and finding yourself by tuning the transmitter, meanwhile swishing all the QSOs in progress. A particularly repulsive AO-40 LID has his transmitter connected to some kind of a dot making keyer that he swishes around over the other QSOs as he tries to find himself. Be considerate. Just go to the high end or low end and find the transmitter, not the receiver.

Once you have found yourself, you will notice quite an echo effect as your signal goes to the satellite and back at a mere 186,000 MPH. It really gets extreme when the bird is 36,000 miles away. The present operating schedule has the bird fairly close, but if this your first long distance bird instead of just another LEO, you will be big time distracted by your return echo. Some people use earphones to eliminate the feedback whine, but    t a l k   r e a l    s t r a n g e   a s  t h e y   a w a i t   t h e   r e t u r n   o f   e a c h    e c h o e d    s o u n d .    Just turn down the AF gain and talk naturally. It will all get there OK, trust me.

After a couple of months of continuous satellite operation, HF seemed strange - the frequency wasn't drifting.

I also feed my external speaker through a ClearSpeech DSP base unit (shown above the TS-2000). The DSP takes all the 2.4 GHz white noise and hetrodynes away, and I can copy someone at the noise floor. The ICOM 910H has a DSP option that when used at level 4 into the Clearspeech DSP it removes all the DSP artifacts of the ClearSpeech unit leaving just the voice on the other end with a trace of distortion. Besides being 2 S units stronger, the 10' dish with its circular feed also seems to have far less fade than the barbecue grill dish's linear feed. An SSTV interface unit connects the Kenwood and SoundBlaster card together for Satellite SSTV Satellite PSK31, and AO-40 Telemetry decoding. It has special SSTV passive bandpass filters to filter out the lids that try to QRM SSTV transmissions and was used to copy the SSTV pictures shown on this webpage. The switchbox at the top selects the 3' barbecue grill dish's output or the 10' dish's output. It also has a $29 Hamtronics 2M preamp & zero gain pad, so if 2M transmit should accidentally occur, the cheap preamp blows and not the expensive downconverter!

If you are particularly successful at getting a good signal to AO-40, sooner or later you will hear a bleeping signal that sounds like a European Ambulance. Welcome to Leila. Your return signal should be 10 db below the strength of the beacon. On the 435 MHz uplink, a special detector called Leila (an a few names less politically correct) will bleep you if you get too strong. Unfortunately the 10 db figure is a moving target, especially so as you are not listening to the beacon when in a QSO. AO-40 and Leila is also picking up some strong 400 MHz RADAR 17 ms pulse signals many times louder than the hams and can be heard bleeping away when nobody is on the bird. So don't let it hurt your feelings if you get bleeped. Think of her as an automatic electronic QSL Card.

Access    http://www.fas.org/spp/military/program/track/pavepaws.htm     to find out what your real competition on 435 MHz is for getting AO-40's attention!

My Suggested Starter System for Working AO-40

Don't be overwhelmed. Start simple and work up to the ultimate system at a later date.

You can buy an all mode rice box for 435 MHz but 2401 MHz is a different story. At 2401 MHz, most coax is more of a resistor than a conductor. So hams on AO-40 mount a device called a downconverter right at the antenna. The downconverted signal now goes through normal coax into the hamshack where it is received on the rice box on 145 MHz.

A wireless form of Cable TV called MMDS operated right next to the 2400 MHz ham band, so hams have gotten hold of the now obsolete ~2400 MHz downconverters, and modified them for ham use. You can also get new downconverters made just for ham use, but at a premium price.

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.

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 for several months.

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). It has programmable line powering of preamps. In the interest of self support, there is no mention of what line powering means in terms of voltage, current, etc. 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.

Amplifiers - Large dishes usually don't need one, but a small, low gain transmitting antenna will definitely be aided by a ~100 watt amplifier at times. 100 watt bricks for 435 MHz are available new or used for around $300 or more. 1296 MHz amplifiers are more expensive. An 80 watt 1269 MHz brick from DL2AM, imported by K5VH costs $490 as a kit. Most 1269 MHz operators with amplifiers use a 2C39 cavity designed by N6CA (shown in the ARRL UHF/Microwave Projects Manual Vol 1). VE1ALQ makes silver plated single tube cavities for $180 and a dual tube version for $280. But with all these amplifers you also need a big power supply. A large BUD is often cheaper in the long run because you won't need an amplifier and you also get a stronger receive signal. I run about 10 watts on 435 MHz and 2 watts on 1269 MHz to my 10' dish for full signal strength. My new 14' dish will cut power requirements in half.

Transmit antenna

First, a little theory.

AO-40's receive antennae are right hand circularly polarized. Transmitting with a left circularity antenna will result in the loss of a couple of S units! Using a linear polarized (a conventional yagi, either horizontally or vertically polarized [makes no difference]) will result in a 3 db loss and a considerable amount of QSB.

AO-40 has a maximum signal strength bleeper called Leila (and a few other things less polite) which will trigger when it detects a 70 CM signal above a critical level. When I use my KLM 40 element right circularity polarized antenna (no longer made) with 15 db of gain (60x), this critical level translates to be between 50 watts and 10 watts from my TS-2000, less power needed when AO-40's antenna points my way (called low Squint angle). With a squint angle < 10 degrees, I can trip Leila with 10 watts on 435 MHz. This is as loud as you can get away with.

Now, translating 10 watts with right circular 15 db antenna as a "Max Desired" under the best conditions is equivalent to:

20 elements - linear array (-3db) @ 20 watts

12 elements - linear array (-6db) @ 40 watts

7 elements "Arrow Antenna" (-9 db) @ 80 watts

Eggbeater (-15db?) @ 320 watts

Remember, these are the powers needed for a maximum signal @ the optimal (lowest squint angle) time. Generally the band is quiet with squint > 20, which requires twice as much power to reach maximum.

Keep your eyes open for an old KLM cross yagi in either the 18 element or 40 element configuration.. Most have a polarity reversing relay that is almost guaranteed to be defective. But a little cleaning puts the antenna into really effective range.

1269 MHz is very attractive, as you won't be directly bothered by Leila (but running too much power and your call will be mentioned with profanity!). The directive Systems loop yagis are popular. I have a 45 element version that claims 20 db of gain. The 10w modules in the ICOM 910H, Kenwood TS-2000 and Yaesu 536R will be adequate when the squint is low. For those who need the feel of power, the kit version of the 80 w DL2AM 1200 MHz brick amplifier costs $500, imported by K5VH (512) 894-4374.

So what does it take to be a power user of AO-40? For average communication conditions, it estimated to be 500 W EIRP on 435 MHz and 1000 W EIRP on 1269 MHz. I usually use my tri band circularly polarized patch feed (described elsewhere on this webpage) to my 10' TVRO dish. On 1269 MHz it has 30 db of gain (x1000). I usually run about 1/3 of a watt during great conditions (close range & low squint), but occasionally run "kick ass" power of 1 watt.

 

AO-40 Receive

Unlike transmit, the bigger the better is the rule when receiving. The most frequently used system is a surplus MDS crystal controlled downconverter modified to receive the 2401.3 MHz signal on 145.3 MHz, looking into a 3' by 2' rectangular barbecue grill dish. Many hams have tried converting on of these surplus MDS downconverters themselves, and those on the air are the successful ones. But unless you are a technical giant, get one converted and tested for you by a technical giant! Then, try your hand at improving.

Bob Seydler K5GNA (281) 852-0252 k5gna@aol.com has a low cost starter system. It is called the "Complete System" for $175. It consists of a 3' barbecue grill dish, a converted and tested AIDC 3733 down converter, 2M xtal, Murata filter, F to BNC adapter, power supply and 75' of cable. Such a deal. Bob recently picked a new downconverter called an AIDC 3731. It's smaller, has a lower noise front end, has higher gain, and with its tuned circuit front end, and has no desensing by your 435 MHz uplink. Bob sells select units with a .89 or less NF & a crystal for 2M output for $115 +$5 for shipping.

Bob Gentler WJ6T ( ) ..... has obtained a large number of MDS downconverters made by a company called "California Amplifier". Bob converts them, adding a crystal which makes the downconversion from 2401.300 MHz appear on 145.300 MHz. The price for this unit is $50 + $5 for shipping. Have soup for lunch and make yourself a tin can patch antenna to attach to your Cal Amp downconverter with a Type N double male connector. Or wind a Helix for your offset fed dish.

For the ultimate downconverter, the SSB Electronic's (570) 868-5643 UEK-3000 is the answer for $460.

All these down converters drift. Leave them on all the time, and cover them with foam water pipe insulation otherwise they drift up when the Sun shines and down when a cloud drifts by.

 

Antenna Mounts and Rotators

AO-40 is up 30,000 to 36,000 miles over the equator most of the time. In the Northern Hemisphere, this translates to a slow moving bird, moving from due East at low altitude, through South at up to 50 degrees, to due West at low altitude.

The 3' barbecue grill dish and 11 element Cushcraft will have about a 10 degree radiation angle, vertical and horizontal. Perhaps 1/2 the AO-40 operators can be heard taking a "turn the dish" break every 15 minutes or so. In the old days, it was "going down the hall" or "getting a cold 807". That's progress. It ain't elegant, but mounting the antennas on a heavy duty tripod is all it takes. Use a couple of plastic protractors for elevation and azimuth bearing indicators. WB6LLO came up with a neat system he calls "Quadpod". Unzip these 2 files for pix & details.

You can get fancy with a couple of old TV rotators from the local ham swap-shop or maybe visit a TV repair shop or talk to neighbors with one. The U100 is popular for elevation rotating.

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 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

On 435 MHz, you get a lot of loss. With weak signals, a small antenna, and low power, you can't afford loss. On 435 MHz transmit, use RG-9913 or hardline. RG-9913 isn't the world's most flexible, but trust me, you want it. On 1269 MHz use hardline.

The down converter is mounted right at the antenna, so common wisdom would say the best coax is not needed. WRONG! The downline frequency is 145 MHz, home base for a bunch of local 2M FM repeaters. The stray pickup of even RG-213 can easily drown out the weak down link AO-40 signal. Use RG-9913 or hardline for AO-40, up & down!

Microphone

Use a "DX" rated microphone. HiFi types irritate Leila; she is much less sensitive to higher frequency audio. The Heil HC-4 "DXer's Dream" element goes for $30. It's always fun to tune the band and find someone with a nice booming bass voice. And though he is an S unit weaker than I am, listen to Leila tell him how much she likes him.

DSP

Guess what you get along with weak signals? NOISE. Get a ClearSpeech DSP unit for $150. It is available in two forms; one version has the DSP unit built into a small speaker. Another version is called a "Base Unit" without the speaker, but same price. I take particularly malicious delight in demonstrating DSP to satellite op visitors. I should get a commission from the ClearSpeech makers. The Noise Reducer option for the ICOM 910H, called the UT-102 is slightly effective at reducing AO-40 noise, and removes some of the DSP artifacts produced by the ClearSpeech so I use both together for "telephone quality" QSOs on AO-40. The Noise Reducer in TS-2000 is completely ineffective on the AO-40 white noise.

Another noise reducing trick is to back off the RF gain of your rig so the AGC does not open up during speech pauses, giving you a swell of white noise.

Cost

Expect to pay between $1000 and $5000 to work AO-40, depending on how fancy you want to be, how much you want to build yourself, and how much you already have on hand.

A basic satellite capable rig will cost you around $1500. If L band capable, add another $500. A ClearSpeech DSP unit runs $150.

A 3' BBQ grill dish will run around $100 including shipping, and various other small dishes will be free to $50. A 30 to 45 element uplink 435 MHz or 1269 MHz uplink yagi will be around $200. Coax and control cables will add $200 to $400.

A 5' to 10' TVRO BUD will be free but takes at least $700 worth of sprockets, chains, bearings, and gearmotors to complete its conversion, taking between a week and a month to complete if working steadily.

The feed system for the dish can be free if you use soup can lids; dual and tri band feed systems take about $25 worth of metal and connectors, but require the tools and test equipment to make and tune. Ready made feeds are available for $200 to $300.

Rotation can be free if done by hand, but most use a $650 Yaesu rotator. Automatic tracking adds another $100 to $500.

You will need a computer to provide basic tracking information. Most hams already have a computer handy which will work fine. A used $200 laptop works fine if you don't have a computer. You will also need tracking software. Some is free, and worth every penny. I use NOVA that costs about $60 to register.

I occasionally make complete BUD systems which sell for around $2000 or less.

 

While this sounds expensive, it is less than an HF rig & amplifier with a medium sized tower, rotator and beam. And working satellites is much more fun; the operators are much more interesting. Even working DX is like shooting fish in a barrel.

Dr. Robert Suding - former Rocket Scientist - W0LMD