# GPS-tracker radio range: how much is enough?

## What is enough range for the rockets you fly?

• ### None of the above- or i'll never need one- please explain

Results are only viewable after voting.

#### FROB

##### Well-Known Member
Hi Folks!
The topic of this week's poll is GPS and radio telemetry;
If you're like me, and you'd like to get such a setup to easily and accurately track your rockets, (or balloons, RC airplanes, or anything else or that matter)
Tell us what you think is the minimum acceptable range either in the air or on the ground (at recovery time)
for your current needs or for what you are planning to build in the near future.

Of course its tempting just to go for the longest range offered but there's a catch you have to keep in mind:
As radio power (range) goes up, so does the cost, the size, and the amount of power it uses.

As an example, lets say for 50,000 feet range in the air (Line of sight) the best designed radio needs ~ 1Watt of transmit RF power- and uses about 3 watts of electricity-
though for our uses it can be run on a pretty low duty cycle, maybe 50:1 or so, so actually ~50mW average power consumption.
Every doubling of range requires at least 4x the transmit power and battery size, and adds significantly to the cost-
at the lower power levels, its maybe 50% added cost, increasing exponentially so at higher power levels, it can go up by 200% or more.

You will notice the range on the ground is listed at about 1/5 of the air "line-of-sight" range- thats a very approximate guess since it depends a lot on things like vegetation, terrain, buildings humidity, and how the thing landed. The point i you should expect the range on the ground to be a small fraction of what you'd get in the air. Normally, if you're getting live telemetry up until it almost touches the ground and loses contact, you just go to the last known coordinates from telemetry and you'll likely re-acquire the signal as you approach.

The question I'd ask you to comment on is, which is the limiting factor in your choice? Is it the range in the air, or the range on the ground?
Again as in my other polls, if this actually bears fruit as a working system, i will draw a winner to receive one "beta" unit from everyone who posts a thoughtful comment on the subject.

Last edited:

#### jderimig

How about a tethered helium balloon (or another rocket....) carrying a repeater to pick up the ground based signal? Then I think you can keep the output power small and economical.

Also the airborne range is going to be very high even with modest power at lets say 900Mhz. The receiver can record the 1 Hz signal on the way down and extrapolate the ground level coordinates after LOS.

#### FROB

##### Well-Known Member
How about a tethered helium balloon (or another rocket....) carrying a repeater to pick up the ground based signal? Then I think you can keep the output power small and economical.

Also the airborne range is going to be very high even with modest power at lets say 900Mhz. The receiver can record the 1 Hz signal on the way down and extrapolate the ground level coordinates after LOS.
Hi John,
thats an excellent idea. A radio relay unit would not be that hard to do once the basic radio is done.
A large toy balloon (like some of the Valentine's day specials i saw yesterday- )
could easily lift one with a small Lipo cell a couple hundred feet - A kite also, if there's enough of a steady breeze, but then you might not want to launch in those circumstances.

You're also right about extrapolating the final position from the history on the way down.
Easy enough to do manually even if the software doesn't do it automatically, though that shouldn't be too hard to program either.

Last edited:

#### bobkrech

##### Well-Known Member
I think I would suggest a combination of methods.

1.) Transmit the current GPS position during the entire flight through a few minutes after landing.

2.) Switch to once every 5 minutes for an hour after the landing.

3.) Switch to once an hour an hour after landing. Stop after 6 hours.

4.) Transmitter actuation of GPS transmitter on demand.

Logic.

1.) If you have a laptop and GPS tracking software, you should be able to track the trajectory of your rocket in real time. While you may not be able to track it to the ground, you can certainly dead reconn the landing site to a rather small area.

2.) Once the rocket is on the ground, the rocket location will not change, so there is no reason to constantly broadcast the transmission.

3.) In all likely hood, if you proceed to the last known projected location of ground impact, you should be within a few hundred yards of the rocket. If you have a hand held remote transmitter, you could trigger the GPS transmitter to send out the rocket location. You should be able to quickly find the rocket if it is intact from that range.

Bob

#### FROB

##### Well-Known Member

It's interesting to note that so far:
- Nearly half of you would be satisfied with something that can do 5 miles range LOS
- For most of the others, 20 miles in the air seems to be the other magic number. Probably a 1 watt radio needed there.
- For the two extremists who want 50 miles in the air, depending on the data rate required, that will likely mean a 4-20W radio;

So the 5-mile one can be license-free, The 20 mile one will likely need an amateur radio license to operate, and the 50+mile one definitely will.
Also, the 50+ mile one will probably be a 2-part affair, which is the 5-mile one plus an external RF power booster.

Is that OK with everyone concerned ?

Last edited:

#### FROB

##### Well-Known Member
Ok, so i'm thinking it should be made to fit in a 29mm airframe.
Does anyone feel it would be really useful to have a GPS tracker smaller than that? If so please give some examples why.

I'll be doing the final board design in the next few days, so now's the time to speak up if you have any thoughts on the subject.

Thanks!

#### TheAviator

##### Well-Known Member
This kind of item strikes me as something that would be used mostly by the large ModRoc (F/G Motors) and up. I don't know what the price point on something like this is, but I wouldn't really want to spend $50 or more (read: expensive) on a GPS system to get back a$20 rocket with a single use motor (read: cheap), especially if it gets hung in a tree somewhere.

That being said, I think you'd be able to capture most of the market with something that could hit 50k. Most rockets stay under that ceiling, and judging based on dual deploy systems and such, you're not likely to see anything drift farther than max. altitude. Therefore, the LOS range is the most important because the landing zone can be extrapolated fairly easily based on the last few data points received, and then the signal can be re-acquired when the receiver comes within range of the transmitter again.

Also, if this does make it to the market, be sure to include special instructions for carbon fibre airframes, as they tend to attenuate RF signals. One of my friends nearly lost a handlaunch glider at less than 200 feet because he forgot about the shielding effect.

Last edited:

#### mattvd

##### Well-Known Member
Is there any GPS solution for less than $300++? If I could find anything even close to$50 I would snap it up in a minute!!

#### Mike Di Venti

I don't think so. Most receivers are about $200 for somethnig decent and could be used for other things as well. i guess one could set up a scanner for the transmitter freq. and track that way. scanners aren't that costly, but can be. #### troj ##### Wielder Of the Skillet Of Harsh Discipline, Potent Is there any GPS solution for less than$300++? If I could find anything even close to $50 I would snap it up in a minute!! Nope. The cheapest way (that I've found) to do tracking of any sort is via Big Red Bee's BeeLine products, with 70cm Ham radios. Their GPS transmitter package is$289 (transmitter, battery, USB interface, antenna -- everything you need, except the receive side).

The challenge is on the receive side. I use a Yaesu VX-2r (~$140) and a Byonics PicPac as the decoder (~$70 for the kit, when they were still available) plus $60 for an Arrow Antenna 7-element Yagi. I've used that solution, and it works well. But, I want to upgrade to the Yaesu VX-8r, which has the APRS decoder built in; that radio is$400.

With the PicPac off the market, you can do the same with a TinyTrak and someone with the electronics knowledge to get an LCD mounted on it (a friend has that combination). Still significantly cheaper than the VX-8r.

In addition, all the BeeLine stuff requires an amateur radio license ($15 to take the test, and the time required to study). If you don't want to invest in GPS, you can buy the BeeLine tracking transmitter (~$90 for the kit -- charger/programming module, transmitter and battery), plus a radio and antenna.

##### Well-Known Member
25k is more than enough
for most of the Florida launch fields....

License free and around $200.- would be a must have.... #### rdmmdr ##### Well-Known Member then you shall have 2 ea. xbee proxsc modules 80.00 the price just went down 1 ea gps engine rated to 30 g's 60.00 rocket side power supply and board 10.00$ 3.3 volt regulator and filter

xbee usb interface board 25.00
cables and antennas 40.00
box 3.00
total 218.00

tracking software is free. "gpsflight is 1200\$", don,t think so.but lets say we wanted to get the altimeter data. add a pic with three serial channels, write the software for the laptops or for another 150.00 just add one more channel and use two laptops. so for 365.00 you get everything

so now that we know the what lets go for the how. take one of the xbee radios and the gps engine (see here)
id_num=11216
and a interface board/power supply(see here)
http://www.makingthings.com/store/accessories/xbee-connector-pack.html

you will not use the side headers. solder the caps, regulator and xbee headers to the board and solder the powerleads from the gps to the regulated outputs on the board. solder the power leads for your 9 volt clip to the unregulated inputs. soldier the rx of the gps to the xbee tx and the tx from the gps to ths xbee rx. attach the antenna to the module and glue every thing to your mount, don't glue the antenna or the xbee in yet. i use 3m 5200 for this , since it holds great and won't corrode the board like silicon can. so for less then any hour you have the rocket side done.

now for the hard part connect a usb to usb mini cable to your laptop connect the other end to the xbeeusb board(see here)http://www.sparkfun.com/commerce/product_info.php?products_id=8687

insert xbee and connect antenna, box optional

for configuring see the tutorial here
http://www.makingthings.com/documentation/tutorial/xbee-wireless-interface

for an hour and a half worth of work you have a working tracker. 215.00 plus shipping

rick
tripoli level 3 11994
tcc