Cross-band Radio Repeater Experiment for High-Altitude Balloon Flights

Overview:

The GPF Balloon Brigade will use an airplane equipped with a trasponding radio in conjunction with ground-based  radios as a means for repeating the ground-based radio signals over greater distances.  The goal is to greatly expand the operational range  of ground-based radios  to aid us in the search for our high-altitude balloons after they fall back to earth.  A cross-band repeater will be placed in the airplane and will send any signals it receives back down to the ground-based radio operators.  The airborne input frequency will be 446.450 MHz, FM; the output will be 146.450 MHz, FM, 25w into a vertical J-pole <or whatever it is>.  By cruising at an altitude of approximately 11,000 feet, the airplane will essentially serve as an extremely tall radio antenna, boosting the signals it receives and sending those signals out to a distance of several hundred miles.

Date:  Saturday, March 8, 2008 (weather permitting)
Time: 10:30 a.m. - 5 p.m. (or thereabouts)
Location:  Rolla, MO and environs

Objectives:

• Determine the approximate size of the “radio footprint” established by equipping an airplane with a cross-band radio repeater.
• Determine if the orientation of the plane used in this experiment impacts the size and orientation of the footprint in any meaningful way.

Experiment:

• Nathan Neulinger will fly his airplane (tail number N1365U) at an altitude of approximately 11,500 feet.
• His plane will carry the cross-band radio repeater. Nathan Bookout (callsign KC0VNP) will serve as the on-board radio repeater operator.
• Ground-based radio operators will periodically send out signals during the ascent and descent of the flight.
• Signals will also be sent out during the cruising phase of the flight at altitude.
• Ground-based transmitters will emit their signals at a frequency of 446.450 MHz.
• Ground-based receivers will pick up the repeater signal at 146.450 MHz
• A “net controller” (Joe Counsil, K0OG) will coordinate the radio traffic between ground-based operators during this experiment. 
• Participants in the radio transmission/reception portion of the experiment are asked to keep radio chatter to a minimum – what we are looking for is the maximum distance between two radio operators when accessing a cross-band repeater stationed at 11,500 feet.
• We will attempt to record the latitude, longitude, and altitude for each radio contact established between participants.

NOTE:

Everyone transmits to the crossbander on 446.450 MHz . Everyone listens on 146.450 MHz .

This is reversed from the convention hams use when using a satellite for communications. In that operation, the radio operator on the ground would be uplinking on the long frequency (146.450) and downlinking on the short one (446.450).

We have to do this on our flight because the UHF (446.450) antenna has too high of SWR for the duty cycle we will have on this flight. This could cause the radio to become very unhappy during the flight (permanent
damage:-)

Flight Track:

One possible flight track suggested by Nathan Neulinger (since its his plane and he's flying it, I guess we'll let him be the one to chart a course) is as follows:

TOTAL DISTANCE: 329 nm (or 378 statute miles)

We will be transmitting APRS (as KC0VNQ-11) information during the flight.

How to Participate:

Contact Joe Counsil via radio (K0OG) or email (k0og@arrl.net).  If you are interested in participating as a radio operator, please be sure to give us your call sign when you contact us.  We will set up a list of participants.

Please give us your transmitter power and antenna type and height above ground.

You will transmit on 446.450 MHz, FM, and will receive on 146.450 MHz, FM.  If you have a radio station capable of working satellites, it will work well for this experiment.  You can also use a dual-band mobile or HT radio, and quickly switch between bands between your transmit and receive.  Another possibility is to use two separate radios, one for transmit on 2m, and the other for receive on 70cm, possibly connected to two separate antennas, or connected to a dual-band antenna through a diplexer.  Do not attempt to connect two radios to the same antenna without a diplexer installed since the transmit power from one radio will feed into the receiver input of the second radio thus causing damage.

What to Expect:

1. Joe the net controller will contact two participants in turn.
2. One participant will respond and will be given clearance by the net controller to attempt to contact the other participant via the airborne cross-band repeater.
3. The two participants will establish contact (or not) with each other.
4. Joe will then repeat this process with another pair of participants.
5. Each contact session should only take a couple of minutes (at most) to complete.
6. We will continue contacting participants until the airplane has landed.

Potential Footprint:

Based on our calculations, we estimate a “radio footprint” of approximately 300 miles or so in diameter.  As the first balloon attempt only traveled approximately 75 miles from Rolla (its origin), our radio footprint should be more than adequate to track the next balloon attempt, scheduled for March 29, 2008. This will also be more than enough coverage to enable the balloon chasers to communicate with each other via radio during the flight. Chasing a high-altitude balloon in flight is similar to chasing a tornado, except that you don't have a nice black funnel cloud to chase. However, considering the fact the next balloon flight is on March 29, which is during tornado season here in Missouri, we may end up running away from tornados even as we are chasing our balloon. In any case, it should be interesting.

Copyright © 2008 GPF Balloon Brigade

Initial Test: Sunday, March 2, 2008

On Sunday, March 2, 2008, the GPF Balloon Brigade met at Rolla Downtown Airport (K07) in order to test the cross-band repeater. We wanted to make sure the repeater worked at all before we unleashed it upon the world at large.

Nathan Neulinger offered the services of his airplane. Bryan Thompson, Ryan Lantzer, and Eric Sigler performed their techno-geekery to make sure they could receive data from the payload, which was placed upon Nathan's airplane.

Mark Bookout (KC0VNQ) and Nathan Bookout (KC0VNP) served as the radio operators for the initial test.

Malcolm Hays took a few photos (see below) and provided some much-needed moral support. Jennifer Song also provided much-needed moral support.

Mr. Hays also found out what it is like to go up in a small aircraft with very strong crosswinds.

It looked (and felt) a lot like this:

Here are some actual photos from the initial experiement (click images to enlarge). Mr. Hays was securely, and permanently, affixed to the ground while these photos were taken.

Longer antenna for lower frequency signal

Shorter antenna for higher-frequency signal

Balloon payload (minus the camera)

Successful landing in vicious crosswinds

OVERALL RESULTS: The initial experiment worked. We got some good data from the payload. The unit switched from its low altitude profile (below 2500 feet) to its higher altitude profile (above 2500 feet) as intended.