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Old Apr 29, 2013, 05:02 PM
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2 mile range transmitter

I am interested in building my own inflight data system with an onboard transmitter. Rather than re-invent the wheel I am looking for a small (tiny) xmitter with a short antenna for use on a sailplane. Should be license free and not directional. Anyone know of schematics or a unit I can buy. It will ne data only though there might be a way using transmitted audio.

Thanks
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Old Apr 30, 2013, 02:42 AM
Stuart
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The range is not a problem, 10mW is enough for about 10kM on 434Mhz or 868Mhz and normally license free, assuming decent RF modules.

The rest rather depends on what you want to do, use a micro controller and RF module you will program yourself, or put together some form of pre-asssembled and pre-programmed module.

And then what sort of 'data' are you wanting to transmit ?
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Old Apr 30, 2013, 06:33 AM
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Brazil, PE, Recife
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xbees 2.4G Pro Series 2 go up to 1km. Then there are the 3DR telemetry radios on either 915MHz or 434MHz. Stated range there is 1 mile, but I reckon this may be a little bit understated. Anyway, you could change the antenna on the receiver to be directional and an extra 6dB should double your range there.

https://store.diydrones.com/3DR_Radi...try-3dr915.htm
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Old Apr 30, 2013, 09:49 AM
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thanks

Actually I have designed a yaw indicator (like a yaw string on a sailplane to aid in turn coordination. ) I will be converting A/D and sending the data stream back to the pilot.
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Old Apr 30, 2013, 10:03 AM
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Illinois
Joined Sep 2001
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Just use a Spektrum radio system and add a custom sensor. There are several threads in this forum from people who have done just that.

Andy
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Old Apr 30, 2013, 08:59 PM
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Quincy IL
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Be sure to check out the FrSky 2.4 Ghz with full down link telemetry. Saves your data on a micro SD card

Less that half the cost of any other system and twice as reliable.
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Old May 01, 2013, 05:27 PM
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New York
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Quote:
Originally Posted by srnet View Post
The range is not a problem, 10mW is enough for about 10kM on 434Mhz or 868Mhz
ahhhhh... snet... snet... snet....
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Old May 02, 2013, 02:37 AM
Stuart
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UK, Cardiff
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Yes me again.

The FSK RTTY 'telemetry' from RFM22 is looking very promising indeed, the FSK Slow Morse has even more potential.

Its difficult to carry out practical full power line of sight tests at ground level due to the curvature of the Earth. However, there is a FSK Slow Morse beacon in orbit (Swisscube) that transmits with the same power as the RFM22, 100mW.

Swisscube can be heard at 2500km, using just an omni antenna and a standard Funcube Dongle.

Coming soon ......... the Lost Model Locator that will receive GPS co-ordinates with Line of sight range greater than 1000km.
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Old May 02, 2013, 03:59 AM
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A satellite isn't a very good comparison. Swisscube transmits at 120mW at only 10 bits/sec, and doesn't have to deal with much atmosphere.

Typical ranges for 100mW seem to be around a mile or two, LOS.
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Old May 02, 2013, 12:18 PM
Stuart
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Originally Posted by jakestew View Post
Typical ranges for 100mW seem to be around a mile or two, LOS.
The calculations around the RFM22 achieving 40km (25Miles) at 100mW LOS, suggest the receive sensitivity was about 7dB below the stated -121dB, so I am convinced there is more range to be had by some further experimenting.
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Old May 03, 2013, 01:21 PM
Stuart
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Originally Posted by jakestew View Post
Swisscube transmits at 120mW at only 10 bits/sec, and doesn't have to deal with much atmosphere.
Atmospheric absorption at the frequency concerned, 437Mhz, is not really significant, although it is at much higher frequencies.
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Old May 04, 2013, 12:10 AM
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Free space propagation losses are certainly significant, and are affected by all sorts of atmospheric factors.

The fact that they don't have to transmit through hardly any atmosphere certainly boost the range.

In any case, you're talking about 2500km ranges when most people are getting 5km if they're lucky. You just don't seem to be grounded to reality in any practical sense.
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Old May 04, 2013, 03:30 AM
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Numbers are numbers, reality check is worse, using RFM22 in OpenLRS system I am not aware about someone to reach 10km to date, without using special antennas...
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Old May 04, 2013, 03:47 AM
I bail out, anywhere, anytime
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The Netherlands, OV, Almelo
Joined Nov 2010
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I see "Old chool" DIY was different than the way it is done these days.
Pre-internet plumber period of clean air and mind, a solder iron and a grid-dipper.
See the photograph. A well tuned oscillator (about 40 years old), free running, was enough to transmit the audiosignal of the variometer over an out of sight range.
Consumption, 9 VDC 10 mA frequency, ++108 MHz.
What was the out of sight range? More than the distance over which I, with a very good sight, could control my glider with a span of 15 ft .

Taurus Flyer
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Old May 04, 2013, 05:35 AM
Stuart
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Originally Posted by renatoa View Post
Numbers are numbers, reality check is worse, using RFM22 in OpenLRS system I am not aware about someone to reach 10km to date, without using special antennas...
As I implied above, I got 40km out of a pair of RFM22s, 100mW, hilltop to hilltop, but I am convinced there is more to come. The telemetry was two way, I was testing the ability to be able to remotely command from one device to another.

The 'special antennas', were 1/4 wave vertical antennas.
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