75mHz RFI issues

[southern or]

Alright, I have 3 stock FM 75mHz controllers and a semi rebuilt F14 controller and ALL of them having chatter issues on all of the channels I have crystals for (around 12 sets). I've tried different receivers but ALL of the controllers, receivers, and crystals are Futaba, even the multichannel decoders. Any ideas so I can do a proper mockup test? I'm REALLY not wanting to pack up all of my operating stuff and searching for a place to setup (servos, motors, dive system with ballast tanks, you get the idea), plus that's a lot of money to be hunting for a clear signal with. The F14 alone is priceless due to it's rarity on the used market and lack of current production for the US market.

[southern or]

Re: 75mHz RFI issues

I should add that I'm using 2 programable (as in they need to be programed) ESCs. That means I need a clean signal or else it won't take.

[Guest]

Re: 75mHz RFI issues

A few things to consider-

1. Are you using original manufacturers crystals?
2. Are the batteries fully charged for both TX and RX? Are you using a BEC, if so what make, and what voltage are you running at?
3. Do you live in an area close to poweful radio transmitters?
4. Are you trying the radio out when runnin gunsuppressed brushed motors?

I never get any chatter with my radio equipment. If you can't get things quiet when running on the bench, it doesn't bode well for when it's in the water.

[southern or]

Re: 75mHz RFI issues

I'm not using a BEC. The plan is to have one ESC power the receiver and servos, then a separate battery for the dive system. I'm looking at 3-4 batteries for the whole setup, 5 if I can track down a Futaba HC receiver battery. Right now I'm testing the crystals (ordered separate, but are the correct make and model) to find a channel that's clearer then the rest with servos only and a low capacity receiver battery powering them. The receiver batteries are always full when I use them and the transmitters have voltage meters built in so I know when they're low. Right now the F14 is at about 80% (AA batteries, funny enough, it also takes a HC Futaba battery that I can't seem to find) and my other higher end Futaba transmitter has a built in rechargeable battery that gets charged with the low capacity receiver batteries (same wall wart charger). Most of the time the chatter is so bad the ESCs can't even acknowledge the signals from the throttles for programing. I'm using Futaba R168DF receivers with Futaba RX SHORT TYPE crystals (Type 72-7)-but I have some long ones too. I haven't bothered with trying them out yet, but I have Robbe multi prop decoders No. 8042. Plus I haven't had time to read about how to set them up yet.

I live on a half way up a hill overlooking Portland and Gresham with someone's microwave receivers (4-5) about 500 feet above me. across the valley (we'll say around 12-13 miles) are a 5 of AM, FM, and Digital TV antennas. Behind the hill are 3 more. I haven't even tested the motors yet so that isn't an issue so far. I also have the luxury of living on the 4th floor (walkup) in a concrete/stick constructed building so shielding doesn't exist. Below us are 6 cell towers, and across the 205 is the MAX with it's suspended power cables at about 1/2 of a mile away, but other then that the power cables for the my hill are buried. The park where I'll be running the sub is only about 5 miles away in the valley floor and is closer to cell towers and the 3 other towers behind us. The other location I've been allowed to use is closer to the 5 towers on the opposite hill across the valley-BUT a out-of-state sub club came and ran there so I "shouldn't" have any issues.

It *used* to be that the FCC fined anyone who's broadcasts bled over into another channel or bandwidth. Having worked at a cable based TV station that got RFI from a FM tower's broadcast I found out just how slow they are to respond to transmission bleeding. took us 7 months to get them to act and during that time we had to only use hard wired mics and lost our ability to use phantom power. It just made it worse. We also had problems with their signal overriding our grounded and hard wired video signal that was on our licensed channels for cable. We broadcast via cable directly to the cable providers so we never sent or received wireless signals-except for wireless mics. After that fiasco, I seriously doubt the FCC will do anything if I file a bandwidth interference complaint.

[Guest]

Re: 75mHz RFI issues

Not sure what to suggest then. Sounds a bit odd to me.

[vasily]

Re: 75mHz RFI issues

We don't have the right to file a broadcast interference complaint for our use of 75mhz. Our use of the RC channels is a permitted use under Part15, but not a licensed use. The language in Part 15 that allows us to use the airwaves reads that our receivers must not interfere with licensed users, and must accept interference caused by licensed users. (That's a paraphrase, but it's pretty close.)
And, even if we did have a licensed right to operate free from interference, the FCC has very limited resources. Licensed ham radio operators sometimes suffer the slings and arrows of outrageous interference, and the FCC can only get to a dozen of the worst offenders each year.
I know you've tested your own equipment, and you're obviously experienced, but have you moved it to a new far away location and tried it there? Do other R/C fans suffer the same interference in your neighborhood?
Jim

[southern or]

Re: 75mHz RFI issues

I thought 75mHz and 72mHz were protected frequencies for hobbyists, so how can you get a license for a channel in the 75mHz bandwidth? I'm just guessing, but wouldn't licensing have fallen then to the manufacture?

As for other hobbyists, most if not all who even used anything other then 2.4gHz have made the switch to 2.4gHz after having operated in AM which is pretty open in this area as a bandwidth but I'm not familiar with AM hobby rights and I've never seen a F-14 or anything close to it in the AM market. I will say this though, the few people I know that operate on FM (about 2) are using 40mHz setups with great success despite that being a closed and illegal hobby bandwidth.

Another rather interesting side note about this area is that between wireless routers and cellphones, 2.4gHs is starting to get crowded. On one of my surface ships for example, it took 3 tries to get the receiver and transmitter to lock. They work fine now.

Thanks for the input so far, but I'm not actually that familiar with 75mHz setups or rules. My background is in TV Broadcasting and even then 99% of broadcasting issues like RFI fell to the station engineer, not the control room or master control crews. I am really good at solving XLR RFI though and that's also a bit of a dying art.

[southern or]

Re: 75mHz RFI issues

Out of the parts and systems I listed, am I running a PCM or PPM setup?

[Guest]

Re: 75mHz RFI issues

I looked up the model of receiver. it's a dual conversion PPM type receiver.

I take it you are using a Futaba dual conversion crystal in the receiver.

[southern or]

Re: 75mHz RFI issues

I'm not sure.

[bob_eissler]

Re: 75mHz RFI issues

Have you tried moving the transmitter a little farther away from the receiver? Sometimes the receivers get swamped by the signal. Disconnect the angle keeper if you have one. They can really get everything upset if they are not set and attached right. Are the transmitters and receivers both set ppm- or ppm+ ?

[chips]

Re: 75mHz RFI issues

I thought 75mHz and 72mHz were protected frequencies for hobbyists, so how can you get a license for a channel in the 75mHz bandwidth? I'm just guessing, but wouldn't licensing have fallen then to the manufacture?

The FCC requires an Amateur (HAM) Radio license for anyone operating on 50 or 53 MHz; the 50/53 frequencies are for any kind of model - aircraft, surface or subsurface. Gear on the Ham frequencies is rare to find now.

No FCC license is required for radios operating on 27, 72 or 75 MHz or 2.4 GHz. The FCC decided a in the late 1980's that 72 MHz would be aircraft only; and 75 MHz would be surface models - submarines included. 27 MHz is open for any model.

FCC Radio Control (R/C) radio service info - two parts relate to the discussion.
"The R/C Radio Service is licensed by rule. Licensed by rule means unless you may operate an R/C station without an individual license."
"You must stop operating an R/C device if the device causes interference."

Here are the FCC regs - Part 95 Personal Radio Services, r/c models are under Subpart C.

[southern or]

Re: 75mHz RFI issues

Thanks so far. I have no idea how to set the F-14 (The one I really need) from PPM to PPM+ or PCM. The decoder has a switch, but the receiver doesn't.

[Guest]

Re: 75mHz RFI issues

It should say on the crystal tab if it's a dual conversion crystal. if it isn't then that is likely to be the source of your trouble.

I don't own an F14, however I do own an FC16, which is basically an F14 with a computer bolted on. The mainboards are somewhat different, however I would expect the tuner to be the same or very similar, as I can't imagine Futaba going to the time and expense of designing a bespoke version.

I've never had any glitching or funny business no matter how close the rig is set-up, so i would be looking at another cause for your interference.

[southern or]

Re: 75mHz RFI issues

Thanks,
I looked a lot harder and turns out that FUTL97 crystals are really meant for a ground controller Futaba made that had 3 channels (3PM X?) and different receiver entirely. I NEED FMC872 crystals which are Dual Conversion. Or so I think.