might a bandpass filter help with 2.4 V-Tx locking out FASST Rx? - RC Groups
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Oct 22, 2009, 01:15 PM
Registered User
lichy's Avatar

might a bandpass filter help with 2.4 V-Tx locking out FASST Rx?

Hey Guys,

So everybody nows, using a 2.4GHz Video Transmitter will make FASST lock out.

I have made a test on a cheap 80$ Spektrum Analyzer, and it looked like this:

Well I'm not an expert, but to me this looks like these two won't interfere with each other, but in fact, they do. So hf-noob me would say, Fasst locks out, because the VTx that is like 40cm away from the Fasst antennas shouts so loud, that the receiver can't hear the transmitter on the ground anymore. I learned the basics of electronics in school, and I know that there is an electronic component that's called a Bandpass-Filter. As far as I understood, using a bandpass, you could filter the frequencys from 2460 to 2500Mhz, so the Fasst receiver wouldn't hear it anymore, meaning it would be able to operate like without the VTx.

So as I said, I know that there is a bandpass component, but I don't know if there is one in the right size, that in fact filters frequencies above 2460 MHz, and I also don't know if this would solve the problem at all.

Is there anybody that is familiar with the matter and would be so kind to exlain it to me? That would be awesome

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Oct 22, 2009, 01:30 PM
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No, won't work, as a bandpass filter hasn't got steep enough filter slopes, nor the small bandwidth required to do it. Just pick another frequency for RC control or video and stop trying to get 2.4 + 2.4 to work, as you will never get the range or flexibility the other solutions offer.


Oct 22, 2009, 02:22 PM
JettPilot's Avatar
A bandpass filter will NOT work, because the video and the FASST system are on the SAME band, the filter will pass 2.4 GHZ video, not block it....

Oct 22, 2009, 06:33 PM
Flying FPV from the lab.
aaron_gx's Avatar
I think trappy said he had great luck with 2.4G vtx on channel 8, avoiding video interference from other's radios, and vice-versa. I know there are a few vtx's that only support 4 channels.

But, sander is right, dont try and force enemies to get along.
Oct 22, 2009, 06:51 PM
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trappy's Avatar
In all cases you need a R/C link that outperforms video in every situation (distance, LOS, object penetration). This means R/C on a lower frequency with better antennas then the video. Having twice the same frequency will get you into trouble even if you get it working.

aaron_gx: Yup, no interference from 2.4ghz buddies. Futaba FASST I had the guy talking to me sitting right next to my patch antenna. Only realized he was on 2.4ghz after we both landed. Spektrum I did get the odd white line ... once every 2 or 3 seconds.
Oct 22, 2009, 07:30 PM
Registered User
mmormota's Avatar
While in theory such a filter is possible, Sander is correct, in real world a filter with acceptable size and price can't be steep enough.

The best separation you can get is setting the switch in the Fasst Tx to "France", this skips the highest channels from the hopping. And set the video Tx to the highest channel. Unfortunately it's not enough, the range is low and there is interference in the picture as well.

Just choose different frequencies for the video and control, no better solution this time.
Maybe later someone develops a time multiplex solution, a wi-fi or similar system for our hobby.
Oct 23, 2009, 02:26 PM
Registered User
lichy's Avatar
Thanks a lot for these great replies guys! I think I'm pretty clear about the situation now.

Oct 24, 2009, 12:31 AM
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videocruzer's Avatar
I took one of the 2.4 systems and asked one of the guys at the radio shop to put it on the scope. the first thing he said was even if we had the equipment that was fast enough to see the hopeing. even if we new where to look you would not even see it.
anyway its what he said
Oct 24, 2009, 04:26 AM
Suspended Account
A FHSS transmitter is almost impossible to trigger on with a simple scope, that doesn't mean there's not signal being transmitted (otherwise your RC control wouldn't work). Ask the guy to try again with a high bandwidth spectrum analyzer and you'll see the FHSS hopping merrily along the band.


Oct 24, 2009, 09:02 AM
Unregistered User
I can confirm what aaron_gx mentioned. If you have a 8ch 2.4ghz video tx there is no radio interference from FASST on the 8th channel since it is just outside the FASST frequency range. But as many has mentioned, far from ideal with regard to signal reception and safety.

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