Amateur Television
Amateur TV can be used for a number of significant ROCKTV applications. Remote recovery is one of the immediately useful. Assuming that the user has remote piloting capability upon descent, the concept here is to guide the returning vehicle to a safe landing spot. In practice this usually means guiding the vehicle towards a field and away from obstacles such as trees, buildings, etc.
There are a number of small television transmitters on the market today. The first major decision is whether to use a licensed or license-free transmitter. License free transmitters are appealing from a convenience point of view. Just hook them up and use them. However, the major drawback is the lack of power and therefore the lack of distance. These transmissions are "line of sight" which means that a clear, direct path is required with no intervening obstacles. The good news is that typical ROCKTV applications are suited for line of sight operation. There is typically nothing but blue sky between the rocket and the receiver. However, license-free transmitters are limited to 100 milliwatts or less. This usually limits the range to about 1000 feet best case.
An example of a license-free transmitter is the Mircotek PIXSEE Handie Lookie. Its dimensions are 4.5 x 2.7 x .9 inches. It can run on a nine volt battery. It is range is between 150 feet and 750 feet line of sight based on the quality of the receiving antenna. It requires a convertor for most televisions to receive its transmission. Because of its restricted range, it has limited usefulness for ROCKTV applications. It is available from PC Electronics. See below.
Licensed transmitters require an FCC Technicians license to operate in the United States. Most other countries require a similar license class. However, the Technicians license require passing a multiple choice test of 55 questions drawn from a pool of 600. Though the material includes technical theory and FCC regulations, children between nine and twelve years old routinely pass the test.
The main advantage to using licensed transmitters is POWER and therefore distance. Even so, investing in excellent receiving equipment is still mandatory. This allows the lower weight requirements for the rocket for a given transmission distance.
Another advantage to licensed transmission is FREQUENCY. There is a happy coincidence in the FCC's frequncy allocations. It turns out that US amateur radio operators are allowed to transmit in the 420 to 450 megaherz range. This happens to include the cable TV frquencies of channels 57 (421.50 Mhz) and channel 58 (427.250 Mhz). Cable TV companies are not allowed to radiate beyond their cable on these frequencies. However, this means equipment designed to receive these frequencies can be used to receive amateur TV tranmissions. This means that TVs and VCRs labeled "CABLE READY" can receive ATV by hooking up the proper antenna and tuning to cable TV channel 57 or 58. (Note that this is not the same as television channels 57 and 58.) This cuts down on the cost of a good receiver. However, there are reasons to use frquencies other than cable channel 57 and 58. The 900 Mhz band and the 1200 Mhz band require dramatically shorter antennas than 420 Mhz which means less drag and more flexible placement options in or on the rocket.
Examples of licensed ATV transmitter candidates for ROCKTV recovery applications are the Wyman AM ATV for 430Mhz, the PC Electronics TXA5-RC, and the Microtek ATVM-70.
Wyman Research, Inc. recommends their FM-ATV for superior operation in radio control airplane and balloon flights. The frequency modulation of the television signal delivers a higher quality picture while far less ghosting and fading. They also have 900 Mhz and 1200 Mhz versions.
Resources:
PC Electronics, Inc. 2522 Paxson Lane, Arcadia, CA 91007. USA (818) 447-4565.
Wyman Research, Inc. 8339 South, 850 West, Waldron, IN 46182 (317) 525-6452