Is there any way to transmit an amateur radio call sign? Firmware change?

I would like to experiment with amplifiers and larger antennas, and possibly with using the 433MHz radios in the US.

I have an amateur radio license here in the US.

Is there a way to insert call sign information into the data being exchanged by the radios? Perhaps by changing the device ID to your call sign or something of the sort? 

It would be awesome if you could just open up Mission Planner and type in your call sign in a box and then save it to the radios and have them transmit it with every data packet. 

Views: 1324

Reply to This

Replies to This Discussion

Sorry, I realize this is a stale thread, but has there been any progress on this? The only other thread I've found with reference to this subject matter was consumed in a fight over appropriate use of GPLicensing. 


I have been giving this some thought. If you use a more powerful ground radio that would require an amateur radio license, it could conceivably fall under the telecommand part 97 rule and you could simply put your call sign label on the transmitter. By using a high gain directional antenna on the ground station, along with a receiver preamp, you could get increased range to the air radio. As long as the air radio is just a stock, part 15 compliant device, it might be a workable strategy for increased range.

Unfortunately, without a way to insert your call sign into the data coming from the air radio, it can't be considered "telecommand" since the air radio isn't sending command instructions like the ground radio, it's only transmitting "telemetry", which would require a regular call sign if the part 15 radiated power levels are exceeded.

Would a MAVLink msg work for this?

I'm sure a new message could be inserted into the APM / Pixhawk code to send just the "Call sign" in text not binary. Could this satisfy the FCC call sign requirement? Looking at the code a see a few (type="char[16]") values that are already in the code to send

"Onboard parameter id, terminated by NULL if the length is less than 16 human-readable chars and WITHOUT null termination (NULL) byte if the length is exactly 16 chars - applications have to provide 16+1 bytes storage if the ID is stored as string"

The way I read, that if a serial window is open, it will show as a readable message in the data stream.

I have seen this question before, and have wondered just what the FCC would consider for a call sign for telemetry radio. 

Myself I have been using a Turnstyle antenna adjusted for 900 Mhz on the plane, and a patch on a antenna tracker. been able to go out as far as 4 miles at 400 ft. I have a set of 1watt radios that make me wonder about this subject.

Well for packet radio and APRS modes, the call sign is transmitted as part of every data packet. If there were a simple way to do this from an end user perspective (enter your ham call sign into a box in Mission Planner) I think it would satisfy the station ID requirement for the air radio. The ground radio should be okay with just an adhesive label for the call sign.

What would be even better would be new firmware for the radios that allowed the call sign to be transmitted, without depending on the flight controller to send it. If the flight controller fails but the radio is still powered, you would still need to transmit the call sign. Current firmware allows users to configure power output, channels, etc. Adding a call sign seems like a natural addition to a future firmware release.

APRS uses AX.25 protocol. I am barely familiar with that, and not at all familiar with MAV link.

Sorry if this is a repeat, it seems I did not post my previous reply properly. For tracking my rockets, I use an Arduino between the GPS module and the data transceiver with a small program that appends my call sign as a header to the NMEA sentences (I also take the opportunity filter unnecessary NMEA sentences).  

KD0GG-11>CQ:$GPGGA.... Then on the receive end I have a Rasp Pi and/or Arduino to strips the header off, parse the data to route non-NMEA telemetry and pass the NMEA string to the tracking app and or Google Earth.  

This is kind of a blend between Burt's suggestion of using the processor in the MAVLink and the X.25 packet mentioned by Ron.

Following the MAVLink path, looks like some work has already been done in this area with the Minim-OSD module. This is primarily for use with a video feed.  This is an add-on extras to the basic fw. Don't know much other than what I've read so far. Will probably pickup a minim-osd module from ebay (<$10) to try.  


On the minimosd, the call sign is entered using the configuration program and stored in the the OSD.

It doesn't get the info from MAVlink messages.

My question was, would it satisfy the FCC requirement for call sign. 

I think getting a new MAVlink message added to the APM and entering it with the mission planner is far easier then updating the firmware in the radios.

Easier for the end user or for the developer?

The issue with it being a MAVLink message is that the call sign must be transmitted at least every ten minutes and at the end of communications. Packet radio inserts the call sign into every packet. If it is in a message that is followed by some other telemetry, and then you cut power, the call sign would not be transmitted at the end of communications.

Updating firmware in the radios using Mission Planner is easy. I don't know how easy coding new firmware might be, or changing Mission Planner to work with it.

The OSD would only satisfy station ID for the video transmitter, not the telemetry radio.

The call-sign that the minim-osd provides should satisfy FCC requirements if you were transmitting video and data on a regulated ATV frequency.  

It probably won't cover us if we were transmitting data using a data modem is on a different frequency (than the ATV feed) or if we are using just a data modem/transceiver without the video feed.  Just my $.02.

Regarding call-sign being transmitted at the end of communication:  I'm not certain that is absolutely necessary with packet radio.  Take APRS for example, the call-sign is transmitted at the beginning of every packet, The systems I've seen do not transmit a final sign-off call-sign before shutting down. 


But I am specifically looking to use 433Mhz telemetry radios in the USA, independent of video. The reason for this is that since the 70cm band is a common, popular amateur radio band, there are tons of great, readily available antenna options, and a host of DIY antenna plans for this band. You can find 900MHz antennae as well, but they are not nearly as numerous as the 70cm band, and there are even fewer DIY plans for yagis and other high gain directional designs as for 70cm. 

For FPV flying and simple telemetry like voltage, current, etc. the video transmitter with callsign would be sufficient.

If you want to use a ground station and higher power or 433MHz in the US, then there needs to be a way for the call sign to be inserted into the data itself.

I was just looking at the code for the radios, looks like this is a area that might be able to insert a MAVlink message from the radio itself.

It sends it's own messages for RSSI and noise both from the local and remote.

Looks like Tridgell wrote the code for it. Looks like this code hasn't been touched for over a year, and most likely if it's not broke don't fix it.

the code is here if you want to look.

It would take code for both radios, update to mission planner for both the radio configuration, and decode the new MAVlink message. 

The other way, would require the same amount of trouble, create a new MAVlink message for the APM or Pix to send out, Mission planner update to config the APM. doing it this way the code for the APM is changing all the time and we might get the developers to do it, as the radio firmware hasn't been updated in years.

I have a set of 1 watt radios that I wanted to find a way to send call-sign for just airborne radio.

Reply to Discussion


© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service