# RTL return altitude and transmitter range

hi,
I have two questions. One is that can I set value of RTL_ALT to more than 80m? please let me know. Randy told me that I can’t. But in My application I need it to be more than 80m. How can set it more than 80m?

Another thing. I need a suggestion to get a transmitter that have 20Km range and that transmitter will also has to be compatible with arducopter. Can anyone suggest me any specific models.?
I am looking for a transmitter that just look like this one they used in this video. Please help me. Thanks in advance.

As far as I know you there isn’t a practical altitude limit for RTL so yes you can set it at more than 80m although as this is for 'copter I stand to be corrected.

Look at the Dragonlink LRS and others like it, see this: bit.ly/1jJ6wH3

@Graham Dyer Randy mackay a developer of ardcopter told me that RTL_ALT Limit is 80m. thats why I asked to be sure. he told me to post the ques. here.
Yes I already google about the long range transmitters. But my ques. is : Is dragonlink V2 is compatible with arducopter? i am working with quadcopter.

And does anybody knows the range of graupner Mc-32? They mentioned that it has a very high range. But they didn’t Mentioned how much they mean by high . So please let me know the range if you know that. and thanks for you reply.

If Randy said the limit for RTL is 80 meters then that’s what it is. He is the lead developer and wrote most of the code so he should know. It seems odd as there is a parameter for RTL to return at the current altitude rather than a fixed altitude. I wonder what would happen if it was set and you were flying at 100 meters and went in to RTL?

Here’s the function that limits RTL alt:

```static int32_t get_RTL_alt() { if(g.rtl_altitude <= 0) { return min(current_loc.alt, RTL_ALT_MAX); }else if (g.rtl_altitude < current_loc.alt) { return min(current_loc.alt, RTL_ALT_MAX); }else{ return g.rtl_altitude; } }```

This function is called at the beginning of the RTL climb and at the beginning of the return. This means that if you set it to 100m, it will climb your copter to 100m and then descend it to 80m during the flight back. I don’t think this is correct behavior - I will talk to Randy about it.

github.com/diydrones/ardupilot/pull/847 will change RTL to return at current altitude or RTL_ALT, whichever is higher. No limit.

We have set the upper limit on RTL to be 80m. The normal default fence height is 100m. That puts it below the 120m (400’) limit used by the FAA, and at 80m the RTL altitude is below the fence height with some margin for error.

The Dragonlink v2 receiver is compatible with APM/Arducopter, it has normal servo connections just like any RC receiver, it just operates on 433MHz rather than 2.4GHz. More information on the product page: dragonlinkrc.com/v2/node/9 (Note that Dragonlink is just the transmitter and receiver, you still need a RC radio.)

Range from a normal modern 2.4GHz RC radio is about 2km line of sight.

here is the code which I got it from here . The altitude limit to come back home is really 80m. and I don’t know why??? cAN anyone answer? or is there any way to change it??

github.com/diydrones/ardupilot/pull/847/files

-#ifndef RTL_ALT_MAX

• # define RTL_ALT_MAX 8000 // Max height to return to home in cm (i.e 80m)

-#endif

You can change the code and compile for yourself