What is the recommended antenna for a gps device like a Yaseu or a Kenwood? Do people use the standard whip or rubber antenna that comes with the unit? I get the last position in the air thing, but what do people do when the rocket is on the ground and the signal is lost? Do people use a long antenna on their vehicle to try to get some elevation? Just curious. Does a Yagi antenna have any use in gps telemetry, or is that only for direction finding of RDF signals.
Hi Chris. Your Space Cowboy had such a beautiful flight, it was a darn shame it was lost - out there at the launch console, I thought we had a pretty good bearing on it too
I use the
Big Red Bee 100mW GPS unit (it is set to radiate at that power). My radio is the Yaesu VX-8GR. I've done a lot of experimenting with this out on the playa and found that:
With the stock Yaesu rubber antenna
With the transmitter on the playa surface, range is 1/4 to 1/3 mile - can't even hear a beep, no data
With the transmitter on top of the Black Rock, reception at the AeroPac launch site is superb - loud, clear, all data. This is ~12 miles.
With an external high gain mobile antenna
With the transmitter on the playa surface, range is 1/3 to 1/2 mile - can't even hear a beep, let alone data
With the transmitter on top of the Black Rock, reception at the AeroPac launch site is (also) superb - loud, clear, all data. This is ~12 miles.
As you will recall, the antennas we have on our RZR are about 6' off the ground. The antenna I use for the VX-8GR is a
Diamond NR770, this has a gain of 5.5 dBi on the 70 cm band.
The NR770 antenna, 38 inches long, 5.5 dBi, mounted on the RZR. SWR is 1.6
I had installed this with the intention of being able to pull in a signal from the Big Red Bee while it was on the ground, or at least, pull it in from beyond visual range (1/2 mile in the heat of mid day). Ha ha. Incremental improvement at best...soooo....I generally use the stock rubber antenna. This has been fine for my current altitudes of ~25,000' and certainly picks up the signal & data throughout the flight, as well as very well during drougefall and under parachute.
The VX-8GR retains the last received packet, so even after when the signal is extinguished by the giant ground plane of the playa, it still displays the last GPS position of touchdown.
When using a 7-element Yagi on the Black Rock, results are pretty much the same as the NR770 - 1/3 to 1/2 mile when the BRB is on the ground. Yech. The place for a Yagi would be ultra-high altitude flights, or in instances when the flight portion has the Big Red Bee in a poor transmitting position (partially shielded, perhaps).
Summary: right now, as fairly typical L3 flyer on the Black Rock, I am happy with the stock rubber antenna. When I move to 2-stage, I will probably return to the external NR770 antenna.
Hope this helps.
All the best, James