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EggFinder GPS to over 50,000'...second time

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High Desert Rocketry

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For those of you with an EggFinder GPS or thinking about getting one, I flew another on another weather balloon to test its range.
The balloon was launched about 25 miles away and the prediction was to climb to > 90,000' and pass over a mountain range. I waited on the other side and began receiving the signal while it was still 5 miles away at 56,000' on its way down.

Both the transmitter and receiver were equipped with the standard thin wire antenna. I did purchase the optional LCD display, I recommend, and black plastic box to make carrying it easier and avoid needing a laptop computer. If you get the Blue Tooth and mapping app like 'Rocket Locator' for your phone it is even easier.

I mounted the receiver in the box so the wire antenna completely fits inside (I hate antennas sticking out of things).

This was our second one on a weather balloon. We had similar results a couple of years ago.

IMG_4629.jpgIMG_4628.jpgIMG_4544.JPG
 
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jrkennedy2

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Were you able to recover the transmitter? Seems like a balloon might go a long ways...

Anyone know an easy signal strength circuit I could put in-line between antenna and LCD? I want to compare wire-stick, rubber-ducky, and flat-panel antennas. Figure I'd put the transmitter on a hill-top, on a pole, a mile or 2 away (line of sight) and see the signal dbs between the 3. Something to try.
 

cerving

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Were you able to recover the transmitter? Seems like a balloon might go a long ways...

Anyone know an easy signal strength circuit I could put in-line between antenna and LCD? I want to compare wire-stick, rubber-ducky, and flat-panel antennas. Figure I'd put the transmitter on a hill-top, on a pole, a mile or 2 away (line of sight) and see the signal dbs between the 3. Something to try.
Anything you add between the antenna and the receiver is going to significantly degrade the signal. Internal RSSI circuits are generally inserted after the filter stage so they don't pick up background RF noise, and have a very high-impedence buffer so they don't degrade the input signal. The Hope RF module in the Eggfinders does have some RSSI capability, but it doesn't work very well... I wanted to put that into the very first Eggfinder LCD software build but it was not reliable. Yes, that sucks... but for the vast majority of rocketry hobbyists the range on the Eggfinder is more than "good enough".
 

kevinkal

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That's impressive with both stock wire antennas. Thanks for posting.

Does anyone know how much power the Hope RF module transmits on the Eggfinders?
 

jrkennedy2

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Anything you add between the antenna and the receiver is going to significantly degrade the signal. Internal RSSI circuits are generally inserted after the filter stage so they don't pick up background RF noise, and have a very high-impedence buffer so they don't degrade the input signal. The Hope RF module in the Eggfinders does have some RSSI capability, but it doesn't work very well... I wanted to put that into the very first Eggfinder LCD software build but it was not reliable. Yes, that sucks... but for the vast majority of rocketry hobbyists the range on the Eggfinder is more than "good enough".
Oh well! Just a hobbyist idea anyhow...

Yep, the range is more than adequate. Just that antennas are black magic to me and the more I fiddle with them maybe the magic will go away. :)
 

OverTheTop

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Putting the antenna inside the box will detune it a little off frequency. The relative dielectric constant of the plastic is different to the relative dielectric constant of air (defined as 1). It "sees" part of the case due to proximity. Because it is off frequency some efficiency is lost. This reduction of signal is on top of any shielding effects, if there are any.

Light travels at a certain speed in vacuum (almost the same in air) but is slowed by other dielectrics.. This makes the antenna electrically a bit short, shifting the tuning up a little. As an example, on a PCB trace the speed of light is about 1/4 of what it is in free air (relative permittivity ~4.2, so factor of 4.2 slower, typically).

Assuming you have some extra signal available in the link budget you will probably not see much change. It will make a difference in range. Not sure how much. With your setup the effect is likely to be minimal because of the slight spacing away from the plastic. The effect would be greater if it was in contact with the case along the length. You will only notice the reduced signal strength at the extreme end of range where signal strength is on the edge of working or not.

What a great test! Thanks for the real-world testing :)
 

High Desert Rocketry

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Were you able to recover the transmitter? Seems like a balloon might go a long ways...
Randy, I've done HAB projects that have gone up over 100,000' and come back down on chute less than 1/2 mile away and others that have gone through the jet stream traveling over 100 mph and carried a long way off. I've always been able to eventually recover the payloads.
 
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