This is the script for the Houston AMSAT Net and EZSATS. Authorization is given for the use of this information over any ham band. Please give credit for the script where credit is due.
|Originator:||Bruce Paige, KK5DO||AMSAT Area Coordinator
|Date Posted to Internet:||3/26/95|
Last time we talked about working some of the satellites that have beacons. Well, what if you have not quite decided to get a satellite station together because you don't really know what you should buy. Hopefully these next few segments will help. Tonight we will talk about some of the satellite radios that are out there and what you should look for.
What type of radio should you get if you want to operate satellites? That's not too difficult a question but there are a lot of choices on the market.
The radio can be two separate radios that are capabable of transmitting side band signals or you can use a specialty radio designed for satellite use such as the Yaesu 736R, the ICOM 970H and the new 820 or the Kenwood TS 790A. Icom has since come out with the Icom 821.
When selecting the radio that best suits your needs, some of the considerations to keep in mind, besides cost are output power, tuning features, and the ease of adding 9600 baud tnc (in case you later decide to work the packet satellites). There are probably more but I feel that these are the primary things that you must be able to do with your satellite rig.
The first feature I consider important is the power output. Besides using the radio to uplink to the satellites, you may also want to use the radio for side band and terresterial. If you do and you are going to use a linear, then you will want to make sure that you can drive the input of the linear to its fullest so that you will get the maximum out of the linear. When working the satellites, maximum power is almost never required. The only times I have found I have to use maximum power is when the satellite offpointing is so far that you can barely reach the antennas. However, if you cannot hear yourself because the off pointing angle is so great, all the power in the world will not help you reach the satellite.
The second feature to look at is how to store a pair of frequencies into memory and then load your VFO later to work a satellite. I have experience with the Yaesu 736R and the ICOM 970H having owned both. The Yaesu 736R allows you to load your satellite pairs. When you select a memory location and want to work those frequencies, the 736R loads the VFO but does not allow you to manually tune it. In order to do that, you must press the Memory to VFO button. This will load the memory contents into VFO but also loads the trash in the VFO into the memory. So to replace the memory with the correct contents, you must immediately press the memory store button before moving the VFO's. Now you can freely move either VFO and adjust your transmit or receive.
With the ICOM 970H, as soon as you select your memory location, the VFO's are immediately available to be tuned with no other adjustment. The problem I have found with the ICOM is that if I want to store a non-standard split, such as those used for operating the Shuttle, you have to first store the main frequency. Then you use the set function and enter the frequency offset. The 736R on the other hand allows you to enter the two frequencies and then save the VFO values to memory. A bit easier than the ICOM.
For Kenwood TS 790A the tuning is somewhere in the middle between the Yaesu and the Icom. You can load your frequency pair into memory and if you want to tune the VFO, you must press the memory to VFO button. The difference is the Kenwood memory locations are not overwritten when you do this as the Yaesu ones are.
The next feature worth looking into is the ability to use a 9600 baud tnc on your radio. Hooking up a 1200 baud tnc is fairly easy. Anyone can connect a few wires to your speaker or earphone jack, one to the microphone jack and another to the ptt switch. The problem with 9600 is you must connect your recieve to the discriminator output and the transmit to the veractor. If you have an ICOM 970H, the mods require no cutting or soldering. The great thing about this is you can always remove your connections if you need to send the radio in for warranty. The Yaesu 736R requires you to solder to a few spots and replace a 10khz filter with a 12 or 16khz filter. This is not difficult but requires a bit more time and is permanent. The new ICOM 820 is 9600 baud ready. The new ICOM 821H is also 9600 baud ready and handles the G3RUH protocol better than the 820 did.
The mods for the Kenwood TS-790A, the Yaesu 736R and the ICOM 970H are available from the AMSAT FTP site.
Now, for the adventerous, you can take two HF radios, purchase two transverters and operate that way. One major draw back is the frequency you tune to. When you tune let's say to 28.105 you must convert that to let's say 145.905. This may is a bit cumbersome, because you have to continually convert the frequency from the working frequency to the transverted frequency. Several people are still operating this way and are very confortable with it. And finally, you can use a VHF radio and a UHF radio.
Both of these final two solutions to operating a satellite are ideal if you already have the radios and do not want to spend much more money on the speciality satellite radio. If you are just starting out in satellite radio, you might want to consider one of the speciality radios. In any case, once you get the equipment and get on the air, you will really enjoy satellite communications and you will learn how your radio works and become proficient at it.
Updated 5 July 1997. Article courtesy of Bruce Paige, KK5DO (firstname.lastname@example.org). Feedback to KB5MU.