| Quick Links |
| Home |
| Propellants |
| Rocket Motors |
| Rockets |
| Rocket Electronics |
| Ground Support |
| Launch & Static Tests |
| Software |
| Links |
| Motor Class Table |
| E-Mail Scott |
| Don't Click Here! |
My next flight will be the the Prelude Rocket, with an expected apogee of over 10,000', it sure would be nice to get the rocket back. Considering the time and money invested in rocket of this size, I think I can afford to spend a few bucks on a radio system.
I looked at a number of systems, some required a ham radio license, others were $600 to over $1,000. After scouring the internet I found Communications Specialists, Inc. The package they sell is intended for model airplanes, but should cross over to rockets just the same. The receiver is about $200, and another $50 per transmitter, not cheap, but certainly not overpriced if they perform.
I was going to see if my hand held scanner would work with the transmitter, but as it turns out the frequency the transmitter operates on is not on my scanner. Probably a good thing too, because the receiver they sell is likely much better filtered and more sensitive than a scanner would be. So I ordered the system, it's nice to see a company ship the same day you order. Why can't rocketry suppliers offer that kind of service?
Here's the system. In back is the directional antenna, below the antenna is the transmitter fitted with the long wire antenna, and three shorter wire antennas. Front from the left is the receiver, rubber duck antenna, spare transmitter antenna nuts and washers, transmitter batteries, antenna nut driver and transmitter battery covers.
When the system arrived, I had to give it a quick test. I installed the longest antenna that came with the transmitter (17") and left the transmitter on the ground in my yard. I drove about 3/4" from my house and gave it a try. At that range, line of sight, the signal came in very strong. So I drove out to over a mile and tried it again, still a good signal, it was getting weak, but no problems picking it up. I hadn't expected any problems line of sight, but what about a worse case scenario, the rocket lands in a ditch?
So the next test I went to our farm pond, the pond has an earth embankment about 7 feet high, then another drop to get to the waters edge of about 8 feet. With the transmitter laying near the waters edge I set out with my GPS in hand. With the receiver set to "close", I lost the signal at about 200'. Switched to "medium" the signal grew faint at about 600'. Switching to long range I set out across the field to find the real range of the transmitter. At about .2 miles I walked into depression in the field so that I even lost line of sight of the pond, the signal remained strong. At about .3 miles out, the signal started getting weak, and at about .33 miles the signal was very hard to pick up. At this range (.33 miles) I was still in the depression and didn't have line of sight to the pond. As fate would have it, there was a grain wagon in the field, so I climbed up on the wagon to get another 8 feet or so of elevation, it really helped the signal strength.
Now I have a good understanding of the limits of the system. Line of sight is well over 1 mile. If there's a hill in the way, or the transmitter lands in a ditch, the range is still a good 1/3 mile. I can see the way to use the receiver is to go to the highest ground and get a fix on the location, then walk or drive in that direction until close enough to pick up the signal continuously.
Polarity is also very important. Not only do you need to aim the antenna directly at the transmitter, but the antenna needs to be rotated to match the orientation of the antenna on the ground. The system really does work great, the antenna is highly directional and should allow a person to virtually walk right up to a rocket on the ground.
I guess the question is; "Does the transmitter have adequate range?". Consider a worst case situation where a flight to 10,000 feet or so hit some fast moving air currents and drifted 1.5 miles from the launch site. I always check the upper level air currents before a flight, so I know what direction the rocket will drift. Simply starting the search by traveling in that direction should quickly bring me in range of the transmitter, by using the track log on my GPS I can easily avoid over tracking an already searched area. The battery life of the transmitter is what really sold me on it, the battery has a life of 4 to 6 weeks. Rather than having to find the rocket in hours as with the FRS radio, I have days or even weeks to perform a leisurely search. The transmitters are fairly cheap at $50 each, and the receiver has some 50 channels. So it's a simple matter to buy several transmitters, one for each rocket.
I've been getting the Prelude Rocket ready to fly, and needed to decide on a location for the transmitter. Finding a good location for the transmitter has been more of a problem than I anticipated. First, the longest antenna is 18", making the package with the transmitter about 18.5" long. I considered mounting the transmitter in the lower body tube with the antenna extending between the motor tube and the outer body tube, but in the event the rocket lands with the antenna down, pretty much all the signal would be blocked by the large aluminum motor. I was also worried about mounting the antenna next to the altimeters in the electronics bay, worried the other electronics would interfere with the transmitter. The next option was to mount the transmitter in the nose cone, but that would require use of the shorter antenna. So another test was in order.
I used the long antenna on the transmitter, and laid the transmitter on a plastic cooler in my yard, about 16" off the ground. Then drove out of town 1.43 miles. The signal was strong at that range, there was a small hill between the transmitter and my location so I didn't have line of sight. I drove out another mile and tested it again, still not having line of sight I had a faint but good signal at 2.43 miles.
I performed the test again, this time using the mid length (13") antenna. At 1.43 miles I had a faint signal, about the same as the last test at 2.43 miles. At 2.43 miles I couldn't pick up the signal at all. So it seems in this case I lost at least a mile of range by using the shorter antenna.
One last test was in order. I decided to mount the transmitter in the rocket and see what kind of range I'd get
with the rocket laying on the ground. I decided to mount the transmitter in the electronics module, extending the
antenna through the lower bulkhead and into the coupler area of the rocket. I glued a 9" length of plastic
tube on the lower end of the module to keep the antenna straight. That left 1/2 of the antenna next to the altimeters
and 1/2 of the antenna in a fairly "clean" area.
Here's the rocket on the ground with the transmitter inside.
This time the assembled rocket was laid on the ground, and I set out to determine useable range. At .63 miles the signal was fairly strong, at .77 miles the signal was hard to pick up. So the real range in the rocket is about .75 miles.
10-19 20-29 30-39 40-49 50-59
10 218.025/ 20 218.275/ 30 218.525/ 40 218.775/ 50 219.075
11 218.050/ 21 218.300/ 31 218.550/ 41 218.850/ 51 219.100
12 218.075/ 22 218.325/ 32 218.575/ 42 218.875/ 52 219.125
13 218.100/ 23 218.350/ 33 218.600/ 43 218.900/ 53 219.150
14 218.125 / 24 218.375/ 34 218.625/ 44 218.925/ 54 219.175
15 218.150/ 25 218.400/ 35 218.650/ 45 218.950/ 55 219.200
16 218.175/ 26 218.425/ 36 218.675/ 46 218.975/ 56 219.225
17 218.200/ 27 218.450/ 37 218.700/ 47 219.000/ 57 219.250
18 218.225/ 28 218.475/ 38 218.725/ 48 219.025/ 58 219.275
19 218.250/ 29 218.500/ 39 218.750/ 49 219.050/ 59 219.300