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Flutter

nterference between 900MHz tx and 72MHz rx

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I have a problem with a 900MHz tx/rx operating on 1watt very close to a JR 72MHz rx (PCM). The range of the JR rx is degraded significantly due to EMI from the 900MHz system (30ft with antenna down on ground test). Since both radios have to go into a 60 size trainer the separation between components is limited. Is there an effective way of "shielding" the 72MHz rx from the 900MHz system? Should I wrap the 900MHz device in copper entirely ;) ?

Thanks

Edited by Flutter

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Any chance you can post detailed photos of how it is installed? It would be helpful to see how the Video gear is routed with the R/C stuff.

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I don't think the shield on the TX would help. Otherwise you would want to shield the antenna too :lol:

You have that 1W TX that blasts lots of RF energy very close to a receiver that tries to grab a very weak signal... Even the frequencies are totally different your 900MHz could still overwhelm the RX input.

From experience (ground tests) I was having significant range drop already with a 500mW TX next to the receiver (tested a few Futaba models). Distance quickly helps (no need to separate by 1m).

A shield on the RX could maybe help. The antenna input is filtered, but the strong RF power could still induce signals on the circuit's tracks... :unsure:

Edited by Kilrah

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Hello Guys,

Years ago I was using 430mhz 1 watt tx. It was a real problem with the tx swamping the rx. I put the rx in a metel box and built a filter that traped the 430mhz out. It worked well. I am now using 900mhz at 500mw and I am not having any problems even with the rx not in a box.

Ricky

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I am currently using about 15" of separation but this doesn't help a lot. The rc rx is not shielded at the moment (emi penetrates shielding???)

The "antenna down" range with the 15" separation is about 90-100ft....but it should really be 150ft +. The radio tx is a JR 9303 and the rx is a JR R770S.

The rc antenna is routed along leading edge of wing and the 900MHz antenna is positioned vertically in aft of the fuselage.

Does anyone know the relationship between antenna down range and extended antenna range?

I don't have a photo of the setup at the moment.

Thanks

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Does anyone know the relationship between antenna down range and extended antenna range?

A huge ratio!

I bet it depends quite a lot on the TX too. Like a friend has a Graupner MC24, when retracted the antenna is still 30cm long. On my Futaba 9Z, the antenna goes in the case, which is grounded, and only 1cm of the tip goes out. There sure is a significant difference.

From my personal experience the generic "100m ground range without glitches and with antenna retracted" rule I often hear is pretty unusable. If I followed it, I certanly wouldn't have taken off once during the past 2 years ;)

Rather than this I'm now using another technique for my ground range tests. I unfold the antenna completely, put the TX vertical on the ground and walk away with the plane at ground height. That sure makes me walk a little more, but that will be my fitness for the day :P

I'll get maybe 200-300m range in that case.

As an example, yesterday with antenna retracted and 149DP RX, I would have only less than 5-10m range. I still had no glitches at all in flight at ~800m though.

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The ground range distance that you use should be available from the radio maker. For example, Hitec advises 30 paces (~75 feet). JR says 60-75 feet. Futaba says 100 feet (30 meters).

A ground range test procedure is found here: http://www.futaba-rc.com/faq/faq-q331.html

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Like Kilrah says. I recon I always fail the ground range test !

It never seems to give a clear indication as to if I will suffer interference.

Terry

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