The Phase 3D Spacecraft

AMSAT Top

P3D - What's In It For Me?

by Andrew A. Skattebo KA0SNL

Think Microwaves

Page 2 of 3

Let's get one thing straight from the start. When we're talking about operating through P3D we're mainly talking about using UHF and microwave frequencies. These frequencies provide reliable communications for our long-distance phone conversations and bring us crystal clear digital satellite television so why shouldn't we be using them to provide high-quality communications for hams? The benefits of using microwaves include compact antennas, almost no background noise and justification for our valuable spectrum allocations.

On the chart, you will see the new "bird" will have a 2m downlink but it has a smaller passband than the higher frequencies and is planned mainly as an interim band for existing operators to use while upgrading their stations. If you're a new satellite operator you won't have existing gear and can plan from the start to take advantage of the higher UHF and microwave bands and the advantages they offer.

Don't let this progression toward microwaves scare you off. Microwave technology is no longer the exotic realm it use to be. It simply requires a new outlook and a willingness to accept new ideas. Most microwave equipment is available off the shelf or in kit form ready to assemble. The most common way of getting active in microwaves is to use transverters. These magic boxes convert your 2 meter or 10 meter radio into a microwave station easily and are relatively inexpensive.

There are many books available with information on building and using transverters and the Premier issue of CQVHF has an article by Gordon Beattie on just this subject. Spend some time becoming familiar with this concept and you'll be well on your way to setting up your own station.

Frequency
Chart

To get a better idea of what frequencies and bands we are talking about using on P3D, take a look at the chart. This gives you the full range of frequencies and the band's associated letter designations. As an example 23cm (1260MHz) is "L" band, 13cm (2.4GHz) is "S" band, etc. If you combine the satellite's uplink (the frequency you transmit on) and the satellite's downlink (the frequencies you listen on) you get an operating mode or configuration for the satellite. For instance, if satellite's operating mode has you transmitting on 1269MHz (L band) and listening on 2.4GHz (S band) then you are operating in "configuration L/S" . Power permitting, it will even be possible to run multiple uplink and downlink pairs at the same time such as UL/VS. Since P3D will have many combinations of uplink and downlink frequencies available, (Any transmitter can be linked to any receiver as long as the two are on different bands) a flexible approach to your station design will keep you from getting locked into a specific operating configuration.

SATELLITE OPERATION PRESENT & FUTURE


Mode B
Station

Right now I have two big antennas to work mode U/V (currently refered to as "mode B") on AO-13, (435MHz up, 145MHz down) a 14 foot antenna for 2m and an 11 footer for 70cm. Around 50 watts of transmit power on 70cm is required to be heard through the satellite. Also there's a high gain antenna required for S band (2.4GHz) receive. These are not exactly very portable and require effort to rotate and maintain. Due to numerous moves in and out of rental units I have been one of those hams unable to set up a permanent "home" station and have limited my satellite operating to a "portable" set up that I can assemble and take down in an hour or two. When I'm home and the weather's nice I throw up the antennas, hook everything up and manually point the array at the satellite . Then when I'm done or the pass is over, I have to take everything apart and store it until next time. This is more effort than most hams are willing expend and does not lead to spontaneous or frequent operation. Also, the large antenna array required and the weak signals received tend to turn off prospective satellite operators. The new satellite has the power to change this picture.


Mode L/S
Station

Figure 2 is a diagram of a future satellite station. You can see that it is configured for L/S operation. This is only for illustration purposes. The design of the station is such that by simply changing receive and transmit converters and their associated antennas you can operate any configuration the satellite has to offer. The basic building blocks of the station are the two transceivers. One is a two meter all-mode radio and the other is a ten meter all mode. I use these as an example because that's what I'm currently using successfully on the satellites and they can be found at reasonable prices for those setting up a station. There are dedicated satellite radios but they are expensive and not really required for the type of operation I do.

For the uplink the 2m all-mode radio feeds a 1269 transverter with an output of 10 watts. A full transverter is not really required since there is no downlink from the satellite on this band but it would be useful for other weak signal work at these frequencies. The transverter feeds its output to a small 12 turn helix antenna about 21/2 feet long. Current information shows that this set-up will provide an adequate signal to the satellite.

On the downlink (receive) side a downconverter converts the S band signal from 2.4GHz to 2m. To use the 10m radio for receive another converter is required to convert the 2m signal down to 10m. A second 2m all-mode could be used in place of the HF radio to reduce complexity if that's what you have. A small 14 turn helix a little more than 1 foot long feeding the converter should provide armchair copy under most conditions. No straining to hear this signal! Comparisons between AO-13's S-band signal and planned performance for the mode S transmitter on P3D show that an even smaller antenna will be enough to copy the strong satellite downlink!

There's your station: two radios, two (or more) transmit/receive converters, and two very small antennas let you talk to a large part of the earth on only 10 watts of power! Of course a few other pieces of equipment are normally used in satellite operation. For instance rotators for aiming the antennas and a computer tracking program are part of most operator's stations. Also, this example does not include equipment for high-speed packet or reception of the digital pictures from the on-board camera. It is the basic, bare-bones example of a station that you can use to communicate though the satellite using mainly voice or CW. It can however, be the building block leading to other modes and bands.

 

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Portions of this article originally appeared in CQ VHF Magazine, October 1996

Contents © 1997 Andrew A. Skattebo

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