Due to the use of a PIC, and improvements in the transmitter subassembly, my new transmitter is much smaller than my previous one.
Inspiration and code for the new smaller board came from Programming Pete's and uses his computer program. Pete uses the Radiometrix transmitter. However, my board uses the new smaller transmitter subassemblies which are available for $7.00 U.S. dollars each when purchased through Quality Kits I use a low quintescent voltage regulator to protect the PIC and to allow 9 or 12 volt batteries to be used. The circuit boards
will work on 315, 418, and 433.92 mhz. You may wish to choose one of
the modules for 315 mHz or 418 mHz to avoid interference from the more common 433.92
transmitters being used at launches. Potential interference exists
from TETRA on 315 and 418 mHz and from various uses including ham radios
on 433.92 mHz. |
( Construction information for the obsolete 6 pin transmitter design are is still available here: obsolete transmitter )
Receiver Construction - Both my old circuit board design and a new one are shown.. The circuits are identical but the new board is 2-sided and much smaller.
Receiving antenna construction
I've been getting requests for transmitter and receiver circuit
boards and PICs.
Contact me at charlesb@texnet/net if
you are interested.
In theory, the whip antenna should be perfectly straight and 15.5 cm long for maximum distance in the air. The antenna should be kept away from the circuit board to prevent serious de-tuning of the transmitting circuit. The antenna itself will be de-tuned when it is in a rocket laying on the ground. In actual practice, I've found that wire between 16" and 18" in length works well on the ground where range is very important.
** It is important to tie a knot in the antenna wire immediately before it exits the electronics compartment so that it will not be ripped from the transmitter if it becomes entangled with the webbing. Also, antennas often don't stay with the rockets when put through a hole and dangled outside the rocket with a few pieces of tape securing them.
Antennas don't radiate well from inside carbon fiber or metal rockets. Both are conductors and kill the signal. (Putting a flexible wire antenna in the airframe so that it will be hanging free at after apogee will tell you immediately when apogee deployment occurs.) If the antenna is in the center of a cardboard or fiberglass rocket, it will tend to radiate better than if it is against one side which is laying on the ground.
Transmitter etiquette is important. Arming the transmitter during prep produces a strong local signal which overwhelms distant signals of rockets which may be landing at the moment. So, the transmitter should be turned on at the last moment and turned off when you reach the rocket. If you know of an active beacon on the same frequency, don't arm.
In the air, the range for the transmitter will be MANY miles. Normally at altitudes of only a couple of miles, the signal will be so strong at first that it will be difficult to get any heading. If the rocket is so MANY miles away in the air that the signal is weak, you should rotate the receiving antenna from horizontal to vertical as necessary while the rocket is in the air so that you can get a stronger signal. An attenuator is helpful for very strong signals.
As the rocket gets closer to the ground the signal will become increasingly directional. (You can place your hand around the antenna loop where it is connected to the coax to short out some of the signal and make it easier to find direction if the signal is overpowering. Or, you can use an attenuator.) In the last 15 seconds of descent (even as close as a mile), the antenna should should be as directional as a gun site so that an exact bearing will be easily obtainable. It is very important to use a yagi to firmly establish the precise direction during this time immediately before the rocket comes near the ground because the signal will disappear when the rocket drops to an altitude of less than 100 ft .
On grass a few inches off the ground, range should be close to 1 mile with a reasonable receiver tuned to the correct frequency. The procedure is simple. Go in the direction of the signal received immediately before touchdown and you will re-acquire the signal when you get closer. If you have the heading, and the distance is great, working a grid pattern at the probable touchdown distance is useful. With a 3/4 mile range on the ground, you can cover a 1 1/2 mile corridor by walking in a straight line. So, if you follow a heading, recovery is easy. Remember to scan at least 180 deg from your left to your right as you travel. Normally the receiving antenna should be horizontal once the rocket has landed unless it is in a tree.
If the distance is several miles it helps to precisely mark the heading on a map which is correctly oriented. Remember, the map orientation and heading marked on it must be precise if this method is to be useful. If you have the luxury of two people tracking, you can draw lines on the map for both headings. The spot on the map where the two lines cross will be the precise location of the rocket.
Vendors:
Quality Kits. (note: Although they show the old version of the
transmitter module on the website, they are actually shipping the new 4 pin
version.) They have been good people to work with. They carry the
new transmitter module and the old receiver module for less than $7.00 each and
the new improved but compatible SAW version of the receiver module for about
$10.00. All are currently on 433.92 mHz.
CommLinx part numbers for these transmitter and receiver sub-assemblies on
different frequencies
are RLP315A, RLP418a, RLP433A, TLP315a, TLP418a, and
TLP433A. (However, the only CommLinx distributor
I've located charges $5.00 for the parts and $25.00 for shipping.)
Digikey sells all kinds of electronic parts i.e. capacitors, surface mount components, etc. at reasonable prices.
Hobby Engineering sells kits to make PIC programmers and has good prices on PICs.