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Interference between 900Mhz: FrSky R9 Slim+ & Sik Radios?

Hello guys,

I have 900Mhz FrSky R9 Slim+ and 900Mhz Sik Radios running at the same time. I have short range on FrSky and a lot of delay on Sik Radios. What should I do?

Use 433Mhz Sik radios.

I’m in the US and was under the impression that 433Mhz was only for Europe, is that true?

I think it is actually. But I used one anyway on a multirotor until I switched to an ESP8266 radio. Of course they are not equivalent functionality with the short WiFi range but with Frsky Passthrough telemetry also it was serviceable.

433 is perfectly legal in the US if you hold an amateur radio license and follow the requirements to operate modem/telecommand radios in the 70cm band. Such as do not use frequency hopping, and do not interfere with 440 repeaters. If you use them illegally in the US without knowing what you are doing, keep in mind amateur radio stations are federally licensed facilities and they have the equipment to track down where you are within about 200 feet. You will be turned over to the FCC if you operate them illegally without a license. Ham radio operators police their bands pretty religiously.

I’ve been using 70cm telemetry radios for several years in the US, call sign AC9KH. Which is another requirement - you must identify your station.

Excellent answer, thank you!

@rolyexpress I use the same FrSky 900Mhz radio system, although with the R9 receiver (not the Slim). It is fairly easy to learn the regulations, take the test and get your Technician Class amateur radio license to operate 433 radios. You don’t have to know much technical radio stuff to get the Tech license, it’s mostly regulations, and what bands you are allowed to operate. The 433’s are the best alternative if you want to use the 900MHz RC.

Another alternative is the CUAV PW-Link WiFi radios. They work on any flight controller I’ve tested them on (they have ground, power, Rx, Tx wires like any modem radio), have a pretty reliable range of ~400 meters out in the open away from 2.4GHz interference. With an off-the-shelf WiFi repeater (“range extender”) at the ground station with high-gain antennas I have gotten 800 meters range with the PW-Link radios. They create an ad-hoc wireless network that you connect to with either your computer or range extender like any other WiFi network. And with a good strong signal with no dropped packets they are very fast.

You could switch over to 2.4G for aircraft control and run an Amp, I think 4 Watts EIRP is the legal max in the U.S… I run this and have a good range for a 2.4G Tx/Rx.

1 watt is the legal maximum for FCC Part 15 with frequency hopping, fed to the antenna, on the 2.4GHz band. It is the same on any of the ISM consumer bands.

The 4 watts of effective isotropic radiated power is a function of the antenna gain, meaning you can run an antenna with a gain of 6dB over isotropic with 1 watt power input (30dBm) to the antenna system. Yielding a total EIRP of 36dBm, or 3.98 watts.

Yes. That is my exact setup pretty much. Sometimes I use a 9dB antenna but don’t tell anyone.:grinning:

9dBi antenna gain is perfectly legal with a 27dBm transmitter (500mW) input to the antenna. With a typical 15dBm WiFi router, for instance, putting out 32mW you can run a 21dBi dish or directional antenna if you want, to get 36dBm EIRP in the forward lobe of the antenna’s radiation pattern.

For point to point it is different. The regulation states that for every 1dBi the Intentional Radiator is reduced below the initial 30dBm, that the antenna gain may be increased from the initial 6dBi by 3dB. So, in other words, for a 500mW transmitter you can run an antenna system with 15dB gain over isotropic, yielding EIRP of 16 watts on point-to-point transmissions.

The answer to range is always antenna gain. Doubling the power input to the antenna only increases gain by 3dB.

My point was I use a 1 Watt 2.4G transmitter with usually a 6 antenna. And have antenna tracker with RFD 900 and patch antenna just keeping myself in the EIRP legal range

In this case, though, the FrSky 900MHz system is being used, which has undeniable advantages on the RC link over using 2.4GHz. It requires longer, or loaded, antennas which is the only real disadvantage.

So Rolando needs to come up with a solution for his telemetry link, as 900MHz telemetry does not play nice with the RC running on the same band, in close proximity to each other.

His current options are to use the ham 70cm band, or 2.4GHz WiFi for his telemetry link. The 70cm ham band is by far the superior choice.

Actually there would be one more option. That is to use 2.4GHz WiFi for short range telemetry link to ground station tablet or computer to set params or load missions. And use the ArduPilot FrySky telemetry on the RC link to the Taranis. There is an open source script for doing this developed by Alex Apostoli

The only downside right now is that if the telemetry link is dropped on the R9 radios due to getting out of range, it does not pick up the telemetry again until you re-boot the receiver. But that being said, I use it and have never had an issue with a dropped link on the R9’s, only when during testing it for range have I discovered the telemetry re-bind issue.

That’s what I suggested and use on Multirotors, a Plane and a Rover. The ESP8266 radios work great for configuration, calibration, mission upload and log download (slow) and along with Frsky passthru on the Taranis I get all I need.

The 433 radio worked fine with the R9 but WiFi is easier to deal with if you have IOS, Anrdoid and Windows ground stations. I should have mentioned before that I have a Amateur Radio License also (K1DKE) which I got a few years ago specifically for this hobby.

I agree, it’s a great solution for the FrSky radios. I have one TriCopter with the WiFi telemetry radio on it and it is blazing fast on param download to the GCS compared to modem radios. It will actually eventually download a log file too, which normally times out on the 915/433 modem radios and fails to download.

I’m moving to R9 as well and was wondering if you observed the same weirdness about telemetry range between frsky native and frsky passthrough, we had a chat about it a while ago.

Actually, Alex, I’m about to test that right now after I got your new telemetry script running the way I like. I just made a short hover test with it so far on the helicopter. I have a limited place to fly from at my shop due to spring flooding and standing water. I had to stand about 15 feet from the helicopter, which is very scary with a big helicopter :grimacing:

I’m going out to the field to do a range test as we speak…

K04HRM here. I am in a similar dillema as rolyexpress. I do have my technicians license however so 433 is an option for me. My question is, “how do you identify when using these telemetry radios”?

The regulations for ham operators are contained in CFR Part 97.215 for telecommand of remote controlled aircraft

Specifically, paragraph a
(a) The station identification procedure is not required for transmissions directed only to the model craft, provided that a label indicating the station call sign and the station licensee’s name and address is affixed to the station transmitter(s).

There is also power limitation of 1 watt, what type of modulation can be used, etc… It is pretty simple, but review the requirements of that section first.

From the practical standpoint, make sure you do not cause interference to 440 repeaters. The transmission from an aircraft telemetry radio will travel a long distance on the 440 band. The telemetry radios are frequency-hopping design and won’t normally trigger a repeater that requires a CTCSS tone to break squelch. Nor will they interfere with normal communications between mobile or fixed stations and repeaters. You can test this with your own 440 rig set up properly with the offset and PL tones required to hit any local repeaters in the area you are flying in.

If you do find that it interferes you can program your telemetry radio to use a fixed channel or frequency that does not interfere (something that Part 15 radios cannot do).

Servers by jDrones