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Project #010 - 430Mhz 500mW Long Range RC Tx/Rx

DISCLAIMER: This design is experimental, so if you decide to build one yourself then you are on your own, I can't be held responsible for any problems/issues/damage/injury that may occur if you decide to follow this build and make one yourself.

The standard 35Mhz RC Transmitter Radio does have a pretty good range if the truth be told, however, when flying FPV the plane can quite often fly well out of sight (video goggles, and a camera on the plane becomes your eyes!). So, I looked around for a ways to increase the power/range of a spare 35Mhz radio I had lying around.

After much research I stumbled upon Thomas Scherrer's 430Mhz 500mW Long Range system (LRS). A system designed for easy 5 - 10miles range! In addition, his system uses a complex wide band multi frequency hopping (FHSS) which makes it virtually imune to jamming, and also an ultra fast diversity antenna switching system (2 Rx antenna) to help when the plane is flying at all sorts of angles etc.
Note: There is actually a 7W booster available, so gawd knows what sort of range that gives! Thomas's webpage is here.

The kit comprises a cased Tx module (c/w whip antenna) and Rx pcb. The idea being that the Tx module is cabled to the buddy port of the radio where it picks up the PPM output of the radio. The Rx pcb is installed in the plane thus replacing the usual 8ch 35Mhz Receiver. There is actually 8ch & 12ch Rx pcb's available, I chose the 12ch version it has an RSSI output (see the DakarOSD article for how I made use of this).

Most folks 'strap' the Tx module to the back of their radio, and possibly a battery velcro'd somewhere. However, I wanted to integrate my Tx Module directly into the radio, and replacing the 35Mhz antenna completely with the 430Mhz whip. I wanted it all completely hidden away, no wires, no mess.
So, I ripped apart Thomas's Tx module to release the pcb's, 1off Tx board and a power supply board. Then I ripped apart my Futaba 6EXP and found space inside it for the LRS.

Some quick info regarding Bind & Failsafe:-

BIND
1. Power on Tx with button pressed.
2. Power up Rx.
3. Recycle power to Tx.

SET FAILSAFE
1. Power on Tx with button pressed.
2. Power up Rx.
3. Set throttle etc to hpw you would like failsafe.
4. Press button on Tx.
5. Recycle power to Tx.

Here are photos showing how I fitted the LRS system to my radio:-

Here's my untouched 6EXP and the 430Mhz kit alongside. You can see the Tx module in it's aluminium case c/w BNC connector for the whip antenna shown, and also the Rx pcb and dual Rx antenna's.

 

After taking apart the Tx module, I revealed the Tx board and power supply board. The black cable is the DC power supply cable, and the 2off small wires coming off the Tx board are for a NO switch used for setup of the system. The short silver cable is the antenna connection.

 

Here's the 6EXP in bits in the next two photos. First thing I did was remove the extendable 35Mhz antenna. The orange board you see is the original 35Mhz Tx amp board which also doubles as the buddy port connector, more on this later.

 

Next, I wanted to make the system as economical on battery power as possible, so I saw no sense in having the original 35Mhz Tx within the radio to be powered up not to mention having to worry about 35mHz channels/xtals. The easiest way was to disable the power to it. I couldn't remove it completely, as I said above it also doubles as the buddy connector. So I simply disconnected the red wire from the solder terminal marked VRF, which is effectively the power to the 35Mhz amp. With this disconnected 100mA is saved.

 

Next, I made up a mounting plate for the new boards using 1.5mm aluminium plate. The holes line up with the 430mHz tx board.

 

And here's the 430Mhz system fitted. The thick black cable you see is coax running up to a BNC connector fitted at the top of the radio where the old 35Mhz antenna was.

 

And here's a small push button switch mounted on the facia of the radio in order to set up the system.

 

Here's a clearer view of the BNC connector and 430Mhx whip mounted nicely on top of the radio.

 

Finally, I changed the battery type and capacity in order to give the system at least 10hrs continious use, more than enough for a days flying. Snipping the small plastic tags in the battery bay gave me just enough room to squeeze in a 2400mAh NIMH 12vdc battery pack.

Ian.