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Welcome to my AO-40 web page! Click on pictures to enlarge image.

    My AO-40 antennas                                                                            Dish and Feed 
a040-ant2.jpg - 59046 bytes ao40-ant3.jpg - 38865 bytes


I began working amateur satellites in January 2002. I started with the FM birds and ISS packet (as many do), and had quite a bit of fun. I even had a voice QSO with Valery Korzun (RZ3FK) aboard the International Space Station (ISS)! This was a great experience, and a great building block!

As soon as I found the linear transponder LEO (low-earth-orbit) birds, there was no turning back! In July 2002, I disassembled my satellite antennas (I moved to a new QTH), and shortly afterwards, RS-12/13 (my favorite bird) perished.

I decided to try the most advanced amateur satellite yet - AO-40! This would be a whole new challenge - I had no experience with frequencies over 70cm!

Many hams believe that satellite equipment is expensive. Not true! Satellite operation *does* require use of a full-duplex rig, or two separate rigs. If you own an all-mode radio, you already have the most important part of your downlink system! This does not need to be a 2 meter rig!

Don't worry if your IF radio is not brand-new or top of the line! Don't worry if you only have an HF rig! For example, I have a simple Hamtronics CA-144 receive converter (2 meters to 10 meters), and have used it to hear AO-40 on my Radio Shack HTX-10 (a Bargain 10M rig)! This unit takes the primary downconverter's output and further converts it down to 29 MHz (2401 MHz to 145 MHz to 29 MHz). You can build a kit (such as Hamtronics), or possibly design your own -- these are simple projects! I may use this arrangement for full-time telemetry monitoring, or to allow another operator to tune around the passband during QSOs. In any case, this makes a decent backup receiver for AO-40!

desk.jpg - 102212 bytes Don't believe it if you hear that satellite operation requires a special $2000.00 rig and lots of technical knowledge. Here is a picture of my radios set up for Field Day 2003. These two rigs make a very capable satellite station, and are able to be run off a single power supply. The only required items not shown in the picture are the dish and converter, and UHF yagi for uplink. The Icom IC-706Mk2G is the uplink radio at MHz, and the Icom IC-245 is the IF radio tuning 145.3xx. BTW, the code key is a special, one-of-a-kind, homebrew item and is not for sale.. hi hi

After you have your downlink working, you can concentrate on building your uplink system. Many options exist here, also! If you do not have a radio capable of 435 MHz SSB/CW uplink, you can use your HF rig, and 'chain' together transmit converters for your 70cm (or even 1269 MHz) uplink!

Even if you do have to buy some equipment, it is possible to build your satellite station inexpensively. If you're willing to spend carefully (buy used equipment, Ebay, etc) I believe that you can have your satellite station going for the cost of a new HT! Which will be more fun to operate?

I was most recently QRV on AO-40 with a 36" x 26" Primestar dish, helix feed, and Transystem AIDC 3731 d/c. My Icom IC-245 serves as the IF radio at 145 MHz, and the IC-706Mk2g is the uplink radio at 435 MHz. This downlink equipment works quite well together, and is capable of detecting the transponder noise floor at reasonable distances and squint angles. It took months of experimentation to discover this combination. The article below details the evolution of my downlink.

This site is mainly geared toward beginners. I have not included complex calculations, etc, just a sample of what equipment and techniques have (or haven't) worked well for me.

Building my AO-40 downlink

I have been receiving AO-40 since November 2002. I began buying surplus satellite TV gear (mostly on Ebay) to modify for AO-40 receive. A lot of surplus equipment is available, and much of it operates around 2.1 - 2.6 ghz, so it is usually pretty easy to modify these units for our 2.4 ghz amateur satellite allocation.

sigsource.jpg - 5973 bytes An essential tool is a 2400 MHz signal source. These are usually very simple circuits, which can be built easily, or purchased in kit form.

The signal source is a great help, as it puts out a very weak signal (ideally at 2400.000 MHz). Listening for this signal will help you to find the downconverter's output signals on your IF radio. For example, if your downconverter uses a 2256 MHz local oscillator (LO) and 144 MHz IF, you should hear the 2400.000 MHz signal at about 144.000 MHz. Remember that most downconverters are very temperature sensitive, and may need to be warmed up to avoid frequency drift.

When first listening for the signal source, listen +/- 50 khz or so. You'll find it eventually! After some experimentation with known frequencies (such as AO-40) you may decide to 'fine tune' your IF frequency using the trimmer capacitor on your downconverter (often located next to the crystal) so that tuning your IF rig is more intuitive. E.g - If you have a 144 MHz IF, 2400=144, 2401=145,etc. Any frequency adjustment you make is multiplied by the scheme used in the d/c (usually 256!)

calamp-i.jpg - 61639 bytes

My first attempt to receive AO-40 was with a California Amplifier brand integrated antenna/downconverter, model # 130003. This unit originally operated from 2500 MHz - 2686 with an IF of 222-408. Unmodified, this unit cannot hear 2400 MHz very well, if at all. Details of the modification can be found here . The modification is explained in great detail.

Many thanks to Fernando, CX6DD for all of the great information. I would not have been successful with my 130003 without his help! Performing this mod also helped me to discover how to modify a different downconverter that I purchased.

Results- This unit is capable of receiving AO-40's middle beacon (just above the noise), and possibly some of the strongest CW, but forget about using this for AO-40 (unless you use this as the feed for a dish - more on this below)

This unit uses a linear polarization patch feed (horizontal or vertical depending on orientation) , and is useful for locating the satellite or dish aiming. You can expect some noticeable QSB on AO-40. This unit also hears UO-11's beacon fairly well.

When first listening for AO-40, be sure to pay close attention to the squint angle calculated by your tracking software. Try listening when the squint angle is as low as possible. FYI- My best receive system yet does not function well above 20-25 degrees squint. If your tracking program does not display squint, try using Predict (Freeware) This software is available for Windows and Linux platforms.

From the Amsat web site: "Experience shows that the S-band downlink signal falls off by approximately 1 dB at 10 deg squint, 3.5 dB at 20 deg and 8 dB at 30 deg. Above 30 deg the level drops quite sharply, and severe fading is also experienced."

The next thing to try was a separate downconverter and antenna. 31732.jpg - 17248 bytes I chose the California Amplifier 31732 downconverter, which was readily available in late 2002. These converters are of similar quality to the popular Drake 2880 downconverters, typical noise figure is 1.7 db. I experimented with two of these downconverters, and found that one heard AO-40 well. It did not work very long, however (more on this below). The second unit did not seem to have much gain, and needed a preamp to hear AO-40 period.

pm.jpg - 73130 bytes Another downconverter that I've experimented with is a Pacific Monolithics model# PM-CTV3301. The company that made these converters is out of business, and I've been able to find very little information about these units, but let me tell you one thing -- These units hear AO-40 very well after a minor mod! The published LO is 2278, and the stock crystal is 11.98947 MHz. I've not converted one of these units to a 144 MHz IF, but otherwise, these units are very capable for AO-40 use! Email me for specific info on the mod! I do not have access to a noise figure meter, so I do not know the NF of this unit.

rhcp2.jpg - 61514 bytes Next, I needed an antenna. I wanted circular polarization, so I built a simple 12 turn homebrew RHCP helix. The helix is easy to build, and the dimensions are not too critical. The circular polarization should eliminate QSB. This unit was made from scrap materials including a length of PVC pipe and an aluminum plate. The total cost was about $5.00, the cost of the type N connector. I had great results with the 31732 converter and this antenna, far better than with the integrated unit. I was able to hear not only the beacon (a couple of S units over the noise!), but many CW qsos and even some SSB (very weak)! It was now obvious to me - I needed a parabolic dish! I'd never experimented with a dish antenna before, and I was intimidated by all of the new terms and abbreviations. F/d ratio, focal point, focal length, it was all new to me!

Putting the pieces together

ao40-ant1.jpg - 63278 bytes I looked around on Ebay, and managed to get a used 18 inch by 21 inch satellite TV dish for about $10.00! The price was certainly right! I had read that a larger dish, one-meter or so is the recommended minimum for AO-40, but I was just getting started, and didn't know quite what to expect. I also thought that this small dish would always work for our higher bands in the event that it didn't work well for AO-40.

lhcp_helix2.jpg - 71814 bytes Now that I had the dish and converter, I had to build a feed for the dish, and assemble everything. I built a simple 5 and 1/4 turn helix, very similar to my standalone helix, but with one very important difference. The dish feed helix is wound LHCP instead of RHCP. The dish reverses the polarization - this is very, very important! The reflector is a scrap piece of metal, and again, the total cost of the feed was about $5.00, the cost of the type N connector.

nconn.jpg - 46957 bytes Assembling the dish feed helix is easy! Howard, G6LVB has a great web site that details how to build a helix and matching section. The helix was wound on a 40mm PVC pipe. I used #10 A.W.G copper wire, and wound about 6-7 turns. I deviated slightly from Howard's plan, using the 3mm chassis connector shim shown here next to my chassis type N connector. Using this shim helps speed construction, although I'm sure the PCB and copper foil work just great also.

After constructing the dish feed and mounting it to the dish, check your work by listening to the AO-40 middle beacon. You may decide later to optimize the helix for your particular dish. This is often accomplished by cutting off 1/4 turn at a time until you're satisfied. If you're like me, you keep cutting until the signal starts getting worse (you cut too much off). Make these adjustments while listening to a weak signal - not the middle beacon. You may end up building a couple of these before you get it just right!

If you have never aimed a dish before, be patient. One thing to know is whether you have a prime focus or offset-feed dish. Most former-satellite TV dishes are offset by about 20 degrees. This means that you'll need to aim about 20 degrees HIGHER than the scale on your dish. E.g - If AO-40 is predicted to be at 30 degrees elevation, aim your dish to about 50 degrees. Adjust az and el to peak the signal.

My dish came with the original LNB and feed strut, so I mounted my feed in the existing location. It was pretty easy, no calculations necessary. All I needed to do is attach a bracket to support the downconverter, and experiment with moving the feed around a little from there. After finding the best position, I used some electrical tape and cable ties to temporarily mount my feed and converter.

After many evenings of testing outdoors, I was finally hearing the satellite really, really well. This was the strongest I'd heard AO-40 yet! Besides hearing the middle beacon (several S units over the noise), I could copy CW (armchair copy) and entire SSB qsos! I began capturing telemetry, and was rewarded with 'CRC OK' blocks, even out to apogee! I was now ready to try my uplink into the satellite! The journey from integrated unit to standalone helix to parabolic dish took some time, and I've learned quite a bit along the way! I'm excited to have gained some experience with microwave frequencies!

On the bird - at last!

After quite a bit of experimentation, luck, and help from many other amateurs (Special thanks to Jerry Brown, K5OE), I was first active on AO-40 in January 2003.

On February 7, 2003, I had a great QSO with Tom Brown, K5UIC. I was using my 18" dish, helix feed, and Cal Amp 31732 d/c -- squints were in the single-digits! This was perhaps the best signal I ever received with the small dish and 31732.

Note: During times of heavy server load, the audio may not stream correctly. Right-click on link as 'Save Target As'. This will save the file to your local disk and provide better audio playback.

Listen to an AO-40 audio clip (MP3 format) - file size 716,115 bytes

The recording quality isn't great, it was recorded analog onto an old cassette player, digitized, edited, and converted from WAV to MP3. Much of the hiss and noise is due to an impedance mismatch between my rig's output and cassette player's input, and improper audio level adjustment. Look for a 100% digital recording of a QSO soon.

Operating via amateur satellites is by far the most exciting ham adventure I've ever had. Each time I work another station I'm amazed that my simple station is capable of making contacts through a spacecraft 35,000 miles away! I have had many QSOs - the majority are from the U.S.A, but I've worked some DX also! So far, I've worked these countries on AO-40:

Argentina           Japan

Australia Canada


Operating notes

My current setup is temporary, the antennas are set up on my back porch, and are aimed manually. To operate from the shack, I had to find a way to aim my antennas when setting up for a pass, and also for the occasional adjustment. It also occurred to me that I needed a way to tune the radio while outside aiming the antenna. I decided to find a way to bring the hand mic from my Icom 706 outdoors! It has UP and DN buttons for tuning on the mic! I was surprised to see from the mic connector schematic in the manual that the 706 also includes audio at the mic connector! ioplug.jpg - 66675 bytes I ran a length of Category 5 (CAT5) twisted-pair cable from the shack to the dish mount, and made sure to clip pin 4 (PTT). This will prevent accidental transmitting through the downconverter. I constructed this harness to connect between the RJ45 jack outside to my headphones and hand mic. This harness also omits pin 4! I have had tremendous success with this setup!

A note about dish pointing: A good way to aim the antenna is by using a weak signal. First, peak the middle beacon, then tune the radio until you find a weak CW or SSB QSO. Peak this signal, and you're all set!

Something else to consider - most folks use a 144 MHz transceiver as the IF rig after the downconverter. Your new downconverter will suffer a certain death if you accidently transmit into it. I've nearly fried a couple of converters just by booting my station computer! The rig is connected to a PC interface, and when Windows boots up, it pulses the serial port pins (RTS or CTS), which is the same way software controls the T/R switch! Be careful of this!

Here's a great solution to this problem! I recently had a QSO with Steve, K6UX, who suggested operating the receive rig in split-frequency mode! This is an easy (and free!) way to protect your downconverter.

My Icom IC-706MKIIG has a wide coverage receiver, but will only transmit on our ham bands. I set the TX frequency to 122 MHz, a spot where the rig will not transmit! Perfect! My transceiver (temporarily) operates as a receiver only, and with no hardware modification! Thanks again, Steve!

Too much gain?

adj_atten.jpg - 6284 bytes Many downconverters have too much gain at the IF frequency. These converters were designed for worst-case situations - long, lossy cable runs, multiple splitters or power dividers, etc. Most of the time in our application, we have too much gain in the shack. I've experimented with several fixed attenuators, such as the 6db CATV attenuator (Radio Shack 15-257 $3.49), but I recommend using an adjustable 0-20 db coaxial attenuator (Radio Shack 15-678, $8.49) . Another idea is to use common CATV splitters for attenuators - most have their attenuation clearly marked on each port.

The reason to use the attenuator is tough to explain, but here goes. A typical downconverter connected to your IF rig will result in an s5 to s7 s-meter reading while receiving no signal at all. Your rig's AGC treats this high noise level as a signal, and many times the rig will accidently mask a weaker signal. In this case, the weaker signal is the satellite!

An adjustable attenuator is great, allowing you to dial down the converter gain until the S-meter reading is about S1 while receiving no satellite signal. When you begin listening to AO-40, the middle beacon will likely show up at about s5-s9 or so.

Another benefit to using the attenuator is that it should provide some protection in the event that you accidently transmit into your downconverter. The attenuator's output should be connected directly to the IF radio, and the attenuator's input to the bias tee or power inserter. This should ensure that the attenuator fails before the bias tee should you transmit. Hopefully, little or no RF energy will travel to your converter.

A BIG development!

ao40-ant5.jpg - 57876 bytes I acquired a much larger dish in March 2003. The new dish measures 36" x 26". It was made for receiving Primestar satellite TV, which is no longer available. I had read that many guys have had great success using these dishes on AO-40, and that often, the dishes are free for the asking! As an added bonus (to satellite ops), some of these dishes were ground-mounted, making removal even easier!

Such was my luck, I spotted this dish near where I work, and after introducing myself to the homeowner, I explained that I am an amateur radio operator, and I'd like to use the dish for receiving radio signals. That's all it took, it was mine - for free! The next time you see a Primestar dish, stop and say 'hi' - you may have the opportunity to tell the public about amateur satellites, and maybe even get a free dish!

I can honestly say that the new dish results in a major increase in received signal, most likely 3-6 db, which is a very big deal on AO-40!

R.I.P. CalAmp 31732!

Shortly after aquiring the new dish, my California Amplifier 31732 downconverter bit the dust. I really had good luck with this converter, I didn't even need to use a preamp. It seems, however, that my results were better than average. On the bright side, maybe now was a good time to lower my noise figure, and otherwise improve my downlink.

ao40-ant6.jpg - 46213 bytes April 2003 - I couldn't let something like a dead converter keep me off AO-40! Believe it or not, I've been using one of the integrated California Amplifier units to feed my Primestar dish, and have made contacts on AO-40! No doubt about it, the integrated unit will work as a dish feed, but circular polarization is preferable, if not required with AO-40. I decided against trying to modify the patch feed into a circular polarization patch. By using this unit as a dish feed, I was able to operate on AO-40 until the one-month shutdown on April 19, 2003. This shutdown happens twice a year, and must be done to position the spacecraft for good solar angles and antenna pointing (squint) angles.

Hello AIDC-3731!

aidc_dc.jpg - 70267 bytes My informal survey of AO-40 users showed that most were using Transystem downconverters. I did some research, and found that the performance of these units should be well worth the cost. These ready-to-use units cost less than comparable units in kit form, and are virtually unmatched by any other unit available. According to Bob, K5GNA, the AIDC-3731 has better front-end selectivity than any other s-band downconverter available.

I recently purchased one of the super-low noise figure models. It features a 144 MHz IF, built-in two stage low-noise preamp, 38db gain and a .9db noise figure! WOW! For more information about these great converters, send an email to K5GNA .

Patch Feed

patch.jpg - 55338 bytes I finally got around to building a patch feed in September 2003. I've found several designs for patch feeds, but I wanted circular polarization, so I decided to try the W0LMD design. Robert, W0LMD has a great web site much of it devoted to dishes and dish feeds A big thanks to Robert for sharing his designs - this is the true spirit of ham radio.

It took just a couple of hour's work to build this feed. If you have access to metal-shop type tools, I'm sure this feed can be made in an hour. I'm quite impressed by this feed! This feed works as well (if not better) than the best helix I've built. I believe that when my dish is tower-mounted, this feed will be low-maintenance. Total cost was about $15 - although I have enough left-over metal to build another patch feed.

I have just begun experimenting with the patch. I will update this section as I make more observations. So far, it seems that the patch illuminates my Primestar dish better than the helix did.

I was receiving AO-40 at 20+ degrees squint on September 20, 2003, and both SSB and CW copy were good. I could not operate above 20 degrees squint with my helix feed. I believe that my helix was underilluminating the dish.


Bottom line, it is possible to hear AO-40 with a small 18" dish (at optimum squint). However, the quality and noise figure of your downconverter will matter more than ever! Take it from me - unless you absolutely have to use such a small dish - Don't! The fact is that copying other stations is difficult, and you risk transmitting over stations that you cannot hear. If the high-gain antenna (S1) aboard AO-40 was operational, I'm sure that the Drake 2880 and California Amplifier 31732 downconverters would have been good enough, and small dishes or stand-alone helix antennas would have worked.

The equipment failures on AO-40 have actually had some positive effects. If a lower frequency (145,435 MHz) downlink was working, many of us (myself included) may not have even considered a 2.4 ghz downlink. We've been challenged to improve our skills and equipment, and become more familiar with microwave frequencies through expermentation. I, for one, was surprised how much information and assistance was available for this band. A great amount of information came from the Amsat-BB.

Another positive effect - those who've built 'AO-40 class' downlinks should have incredible results with future satellites carrying S-band. Just think how well you'll hear Phase 3e if it uses a high-gain antenna on s-band!

One great quality of our higher frequencies is smaller antenna size. A 144 MHz antenna capable of hearing AO-40 would be much too large to carry for rover activity, field day, etc. In contrast, a one-meter dish will fit in most vehicles, and can be set up in just minutes!

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Last Updated September 6, 2012
©1997-2007 Kyle Yoksh