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FPV 1.3ghz + RC 2.4ghz tx Interference

#1
I flew my wing around with no fpv plugged in. I plugged it in and did some tests everything seemed fine. I took off, flying straight out for about 10 second when i looked at my monitor and started flying fpv. The plane started to tilt and nosedive and I moved the controls and nothing happened. I moved the sticks to the extremes and nothing. My plane impacted the ground splitting it in half. The only logical explanation is that my 1.3ghz Ready Made Rc tx interfered with my frysky module modded turnigy 9x, but everyone else who has this setup has not experienced this. Is there any explanation?
 

PaulT

New member
Mentor
#2
Since you are running your fpv frequency lower than your radio I would suggest getting a harmonic filter.
I have heard of this before and most people I have talked to run a higher frequency for the fpv for this reason.
 

lobstermash

Propaganda machine
Mentor
#3
Partially right there, Paul. The 1.3 system puts out harmonic interference as well as noise in the 2.4 spectrum. A low pass filter will take out the latter, but you'll get harmonics pretty much regardless. 900Mhz is fine with 2.4 with a low pass filter.

Many people who fly with 1.3 use 433Mhz or 72Mhz for control.

The more detailed explanation is that up close, everything is fine because both radio systems (control and video) are receiving most of the signal being transmitted, so if there's a harmonic or noise, the next radiowave will hit the tx fast enough to make the interference unnoticable. However, as you get further away, much less of the signal is received and interference becomes more exaggerated. Typically the lower frequency wins, so you get to watch perfect video while you crash. The interference usually starts hurting the control signal at around 500m or so (varies with the quality of the antennas/equipment) and if you've got the telemetry FrSky gear on board your transmitter will start beeping at you.
 
#4
1.2 GHz FPV and 2.4 GHz RC don't work that well. You can try to use a lowpass filter but that does not always works. You are better of buying an UHF system (433 MHz) or an 72MHz radio. UHF systems are expensive but have great range and 72MHz radios are great to but have less range then 433MHz rc but more range then 2.4GHz RC.
 
#5
Apart from the frequencies being a close multiple of one another, polarization always plays
a significant role in the interference and harmonics you are going to get.

For example, if you have a video tx at 1.3GHz and an Rx at 2.4GHz both with vertical polarization
you will have strong signal interference and probably crash. Changing the polarization of the two
frequencies will allow you to get much better results. Adding a lowpass filter helps a lot, too.

Next time mind where your video antenna is pointing and point your 2.4GHz Tx antenna 90 degrees
vertical to it. This will ensure the polarization is different, thus minimize interference as much as possible.
 

PaulT

New member
Mentor
#6
Is getting things partly correct the same as party incorrect?
Thankfully there are always smarter people than me, on here.
When I was started to look at FPV, this was a common problem that Darren has experienced, and was mentioned in quite a few search's I did on the net.
"so you get to watch perfect video while you crash.":D
 
#7
I have seen plenty of people with success with my setup and I knew about harmonics and possibility of interference but I overlooked the need for a low pass filter as I thought everything would work fine. Boy, was I wrong and I certainly paid the price for it. Despite that though, I learned my plane is a perfect fpv platform and with further tuning I may, someday, be able to have a successful flight.
 

lobstermash

Propaganda machine
Mentor
#8
Is getting things partly correct the same as party incorrect?
Haha, the public servant in me coming out... The partially incorrect bit was in regard to higher/lower frequency. There's nothing wrong with using a lower/higher frequency for control than video, as long as you choose the right frequencies and equipment.

I had the perfect video while crashing once when I flew directly behind myself while hunched over the tx! It prompted me to go FrSky, so that it beeps at me when the signal weakens.