Hi C

It looks like your "wire" antenna might actually be OK for your project.
You have demonstrated that it works when the rocket is nearly 10 miles
away
when you hoped for 20 miles. Evidently, the antenna doesnt need to
function while the rocket is accending.
Are you able to improve the ground based antenna The equipment you now
have would need only 6 dB improvement to provide the 20 mile range.
I'd like to know more about your ground based antenna system.

Jerry KD6JDJ (who has lots of small
diameterTeflon dielectric coax to donate to a real project)

Jerry:

The "ground station" is not much; just a small receiver with a
standard 1/2 wave dipole attached using an sma connector. The
receiver is battery powered and connected to a laptop using a standard
serial cable. We had thought about using a Yagi during the previous
flight but it just got left by the wayside with everything else that
had to be done.

The basic telemetry and downlink system is manufactured by Ozark
Aerospace (Erik Hall) but uses a Digi Int. 9Xstream radio modem
(www.ozarkaerospace.com and I use the ARTS TX-900G and RX-900). I
actually built my own transmitter and GPS system using a 5 watt data
radio and Garmin GPS with a small Li-Ion battery pack. But that system
was "lost" during a not so successful flight in Texas a few years ago.
Hence, for this design I opted to buy something off the shelf that
already worked.

Most people using this system have fiberglass airframes so for them it
is a simple matter to use a commercially available antenna mounted
inside of the airfame. But this is an all metal design so I had the
telemetry board made so I could connect my own antenna. FYI, the
rocket is 15 feet long, 6" in diameter and weighs over 100 lbs empty
and close to 200 lbs. on the pad. It is all aluminum, except for the
nose cone which is laminated birch. I'm using metal for the airframe
because it just easier to work with and the first 8 feet of the rocket
is metal anyway as that is the motor case.

The published range for this Digi Int. transmitter is 20 miles, though
people doing amateur high-altitude balloon flights have reportedly
observed even better reception from high altitudes (i.e., over 80 K
feet). This rocket did about 85,000 feet last September at Black Rock,
Nevada so it is doubtful that we will get GPS data at apogee anyway
due to the COTS limitations. But I'd like to get as much as possible
and will probably eventually convert to the 9Xtend modem which goes up
to one watt xmit power.

Curt

Hi Curt

I strongly suspect that you can use the antenna you now have on the
rocket. There is a possibility that you hadnt optimized the pointing of the
stub on the base station. You might be able to get enough system gain by
using a simple Turnstile Antenna at the ground station ( Wikipedia ).
If you decide you want more signal than you get with a Turnstile, it would
be easy to build a 900 MHz Helix or Crossed Yagii.
It seems very important to use a Circularly Polarized antenna at the
ground station.

Jerry