Cross band repeat with a ham radio handheld and a drone

[AZDave]

There a few small and relatively inexpensive handheld VHF/UHF ham radio dual band transceivers that have cross band repeater capability, and they are light enough that with a bit of difficulty a drone (I have an MA2) should be able to carry it aloft for a short while. In theory, a person on the ground with a handheld radio could transmit to the radio suspended under the drone on, for example, a UHF frequency and the radio under the drone would translate that to a VHF frequency for immediate retransmission. Somebody miles away would hear the VHF transmission, transmit back on VHF, and the radio under the drone would translate back to UHF for the person on the ground. This might be useful for communication in a hilly, semi-remote area since the drone could legally be flown up to 400 feet above the nearby hill. I'm just curious if anyone has ever tried something like this. I know there are hams who have been camping in a valley and have hiked up to the top of a nearby hill to set up a cross band handheld for exactly this purpose ... it just seems like a drone would be easier and more effective for temporary use.

Just a thought ...

 

[SkyeHigh]

The output from the transceiver, though on a different frequency band, could easily swamp the receiver input on your drone with such close proximity.

 

[AZDave]

The output from the transceiver, though on a different frequency band, could easily swamp the receiver input on your drone with such close proximity.

Almost for sure not. The frequencies are WAY different, the output power of the handheld is a few watts, and the handheld antenna is inefficient. There is a wireless ISP that uses my ham radio tower and some of his equipment operates on frequencies similar to what the drones use. I can transmit with over a thousand watts to antennas on that same tower and his stuff doesn't blink an eye.

In any case, it would be a simple matter to test it ahead of time instead of just speculating like you did.

 

[SkyeHigh]

Almost for sure not. The frequencies are WAY different, the output power of the handheld is a few watts, and the handheld antenna is inefficient. There is a wireless ISP that uses my ham radio tower and some of his equipment operates on frequencies similar to what the drones use. I can transmit with over a thousand watts to antennas on that same tower and his stuff doesn't blink an eye.

In any case, it would be a simple matter to test it ahead of time instead of just speculating like you did.

I’m not speculating. I spent much of my life as a transmission engineer. I wasn’t an amateur. It’s not just the frequency that matters.

 

[AZDave]

I’m not speculating. I spent much of my life as a transmission engineer. I wasn’t an amateur. It’s not just the frequency that matters.

And I got my degree in electromagnetic field theory, spent my entire work career in RF and other electronics, and have been an active ham radio operator for 56 years ... building much of my own equipment.

 

[SkyeHigh]

Yeah, Whatever.

 

[Skydreamer]

how can radio signal interfere with drone signal if both are on different frequencies?….i am thinking drones being used to inspect cell tower,radio towers etc

 

[GFields]

I have removed a few rude posts and will close this thread down if it continues. Stay on topic and stay civil. Thanks

 

[KB9Radio]

It would be a a very short term cross-band repeater, however in the case of getting an emergency message out would probably work pretty well. You would want to suspend the HT in a way that would keep the antenna vertical, or mount an antenna on the drone and connect it with a tiny coax. It may cause some interference between the drone and controller but you would probably be hovering at that point and it wouldn't make any difference. You could set up the vhf for a distant 2-meter repeater where your odds are better someone is listening. Sounds like an interesting project, I'm trying to think of some ARES use for it.

 

[Skydreamer]

It would be a a very short term cross-band repeater, however in the case of getting an emergency message out would probably work pretty well. You would want to suspend the HT in a way that would keep the antenna vertical, or mount an antenna on the drone and connect it with a tiny coax. It may cause some interference between the drone and controller but you would probably be hovering at that point and it wouldn't make any difference. You could set up the vhf for a distant 2-meter repeater where your odds are better someone is listening. Sounds like an interesting project, I'm trying to think of some ARES use for it.

how,what would cause interference?

 

[jimlips]

how,what would cause interference?

Any relatively high-level transmitted frequency can overload (or "desense") the front end of a receiver in close proximity - it doesn't necessarily have to be in the same frequency band. Just from experience, I would recommend giving it a try and report back so the rest of us can benefit. Sounds like a fun project. I've got a Yaesu FT-530 that does cross-band repeat, but it weighs over 1 lb (516 grams). Not sure what the limit on my drone is. I have tried lifting objects with my Phantom 3 Advanced, it seems to have the most power. But I'm not sure about what my Mavics can lift.

 

[Felix le Chat]

Just spitballin' here.
In America: the FCC (Federal Communications Commission) determines a transmitter power of up to but not in exceeding 1,000mW or +30 dBm.
In Europe: CE (Conformité Européene) determines a transmitter power of up to but not in exceeding 100mW or +20 dBm.
DJI drones are set to broadcast the control signal at a lower strength than these maximum limits.

FCC: ≤26 dBm at 2.4gHz:the same at 5.8gHz.

CE: ≤20 dBm at 2.4gHz and ≤14 dBm at 5.8gHz.

If your transmitter is "...a couple of Watts..." - at full legal stretch: the drone would only be transmitting at 1 Watt (1,000mW). The actual transmitter power is less than 1 Watt. If you strap it to the belly/back of the drone: I wouldn't be surprised if the "couple of Watts" walkie talkie signal swamps the control signal.

Best way to safely test this? boot up the drone & controller, flip to the TRANSMISSION tab in the menu. Put the hand-held walkie right next to the airframe and key-up. If the graph goes bananas... there's your answer.

Take a look at the black sticker inside the battery bay. Left sidewall.

Quote. "This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions. 1. This device may not cause harmful interference and 2. This device must accept any interference received. Including interference that may cause undesired operation." Unquote.

 

[KB9Radio]

how,what would cause interference?

Even if you're only transmitting 1 to 2.5 watts, you're only an inch or two from the drones antenna and it wouldn't be surprising to get some desensitization in that situation. The further away away you are from the drone, the more desense would affect the link to the controller. Even though the drones operate at 2 & 5 GHz bands, they also run very low power I'm sure. So depending on how good of band pass filtering they have, a vhf/uhf transmitter a few inches away could easily affect it some. Even when the HT on the drone is receiving, it will be simultaneously transmitting back to your HT on uhf. Antenna spacing is important and on the drone you won't really be able to get much space at all. It might not bother enough to notice at all. Like I said, it will be an interesting experiment.

 

[Cafguy]

It is done and your only obstacle really is are you properly licensed by the FCC to use such a system? IF SO then remember --The antenna goes to the Back.

Much better done with Balloons Really.

 

[AMann]

I’ve done it with an Alinco 1/4-watt credit card 2M HT and a RadioShack simplex repeater controller - …I’ve done it with an Alinco 1/4-watt credit card 2M HT and a RadioShack simplex repeater controller… - that was fun and it worked very well if you don’t mind the mirror reply and delay created by using a simplex repeater- …that was fun and it worked very well if you don’t mind the mirror reply and delay created by using a simplex repeater…!

I didn’t notice any desensitization affects on the M2P, and the radio was sitting sideways with the mini duckie antenna sticking off the side.

Also thought about using a little ATV transmitter and camera on it as well, but that project is on hold for now.

 

[Cafguy]

Also thought about using a little ATV transmitter and camera on it as well, but that project is on hold for now.

I have a Mavic Pro 1 that I didn't want to buy a new gimble and camera for, So I Hot glued an old Cinewhoop Stack on it and a nano-Cam, It all runs on a 2s battery stuck on top with velcro.
Works like a champ with my old FatShark goggles. Not alot of camera range though but enough to fly around the small park.

 

[AZDave]

Even if you're only transmitting 1 to 2.5 watts, you're only an inch or two from the drones antenna and it wouldn't be surprising to get some desensitization in that situation. The further away away you are from the drone, the more desense would affect the link to the controller. Even though the drones operate at 2 & 5 GHz bands, they also run very low power I'm sure. So depending on how good of band pass filtering they have, a vhf/uhf transmitter a few inches away could easily affect it some. Even when the HT on the drone is receiving, it will be simultaneously transmitting back to your HT on uhf. Antenna spacing is important and on the drone you won't really be able to get much space at all. It might not bother enough to notice at all. Like I said, it will be an interesting experiment.

There is nothing that requires the HT to be only an inch away from the drone's antenna. It could be suspended 3 feet or 10 feet or even 50 feet below the drone via a string, and of course (neglecting reflections) signal strength is an inverse function of the square of the distance.

The uneasy aspect of actually testing this is that the most likely scenario for a problem would be when the signal from the RC is weak ... meaning that the drone should be relatively far away from the controller. That makes for an awkward test unless two people are involved, and if only one person it could be difficult to retrieve the drone if something goes sideways. But Cafguy in his post above says it works even with the HT riding piggy back on the drone so I have my answer.

 

[Cafguy]

There is nothing that requires the HT to be only an inch away from the drone's antenna. It could be suspended 3 feet or 10 feet or even 50 feet below the drone via a string, and of course (neglecting reflections) signal strength is an inverse function of the square of the distance.

The uneasy aspect of actually testing this is that the most likely scenario for a problem would be when the signal from the RC is weak ... meaning that the drone should be relatively far away from the controller. That makes for an awkward test unless two people are involved, and if only one person it could be difficult to retrieve the drone if something goes sideways. But Cafguy in his post above says it works even with the HT riding piggy back on the drone so I have my answer.

Also the Antenna Hint comes from someone who told me that if you face the antenna forward it could cause trouble with the front Sensor on some Drones. not sure if it helps in any other way.

 

[jimlips]

This sounded like a fun thing to try, so I did. I hung my FT-530 (Yaesu HT - capable of cross-band repeat) about 6' below my DJI Phantom 3 Advanced via paracord. It worked, and my buddy said I was full-quieting about 5 miles away (on low-power setting).

Not really practical for finding a lost hiker - esp. with my batteries from 2019 - they normally only last about 15 minutes, and with the extra weight (16 oz), they only lasted about half that. But it was a fun challenge!

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