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relee

extreme a/v noise @ heli cam

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Hello experts,

converted during last week from a (50 Euro) 2.4 GHz Tx incl. cam to separate building blocks - but the result is awful. Did yesterday a range check with just the 2.4 Tx + Rx + cam and everything was beautiful. Today I combined the video gear with my heli and the result is quite shocking :angry:video shows the landing of the heli, when the noise gets less

Here are the details:

2.4GHz 100mW audio/video transmitter (TM-240200mini)

Yellow Jacket Standard Diversity Receiver with 2 2.4GHz 3dBi Rubber Duck antennas

SONY 520 Line cased camera (PAL)

Heli: DNHP Centurio

Blades: SAB 620mm CFK

Controller: Quick RAY 90A

motor: AXI4130/16 gold line - brushless outrunner

CCPM servos: JR/Graupner DS8231

gyro: FUTABA GY-401 with S9254

Heli Command 3A

RC Rx: SMC20DSCAN 35 MHz

RC Tx: MC-22s JR/Graup. 35MHz

The white + yellow wires (audio + video) go directly from the cam to the 2.4 GHz Tx. The cam uses a 11.7 V (LiPo) and the ground lines are shared with the Tx (otherwise the video Tx quality was poor). 2.4 GHz Tx is on it's own battery (shared ground)

I do have 2 or 3 suspicions:

1) both cases (cam + Tx) do not share the same physical ground; only the electrical

2) the audio / video signal cables are non-shielded - due to the provided sockets / cables

3) the Tx antenna might be - due to it's soldering - defined to catch noise (only applicable within heli)

4) the main chassis has a common ground - the cam + Tx are on a epoxid platform - which has no mechanical ground

Interestingly: the noise starts as soon as the motor / blades start running; when the heli lands, and the motor stops the noise get's dramatically less - but as you can see within the video - it's not completely gone, till the main rotor slows down

Would anyone have the personal experience, that the given Tx with the flexible antenna can be changed to work with a SMA based rubber duck antenna?

Any advise would be greatly appreciated.

Cheers,

relee

post-5-1191278806_thumb.jpg

Edited by relee

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Some A/V transmitters do not support loud audio noise driving the microphone.

Here is a simple bench test to try: Clap your hands very loudly, directly in front of the microphone (get as close as you can). Do you see video noise that corresponds to your clapping?

The solution may require mic removal. However, you can experiment by isolating the mic from all hard surfaces. Also, try burying it in foam.

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I'd say either what Mr.RC-Cam said, or just mechanical vibration on the transmitter. Some HATE that. You can try tapping the transmitter case to see if it causes lines, that can be enough. If it's the problem, go and fetch a good pack of foam and wrap it inside, ensuring there's no rigid link between the TX and the heli.

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The video looks very much like sound noise to me so I would go for removing the mic first as Mr RC-Cam says but the same interference can be from vibration as Kilrah says so mounting in foam would be good too. After that it only leave interference from a shared battery but I think you say it is not shared with the motor ?

I would tie that aerial to somethink too to stop it waving in the wind.

Terry

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Thanks folks,

vibrations are not the cause. This heli is extremely vibration arm - check it out on youtube.com author "DreleeD" - all movies for "DNHP Centurio".

Thanks Mr. RC-Cam for your hint on the microphone. CONFIRMED ISSUE clapping

Any good advise on how to remove / isolate the mic?

Trillions of thanks to you folks - who get us newbies going.

Cheers,

relee

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If the mic is in the camera, then the audio signal would normally be the white wire.

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Thanks again Mr.RC-Cam

Issue fixed by removing the white (audio) signal - the audio wouldn't have been of too much help inside the helicopter anyhow ;)

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I sense the pest got me .... :blink:

simply cutting the audio line between the cam and the Tx was fixing the "clapping" .... but when I took the gear today to the field .... still noise :angry:

I must admit, I'm a "digital" person ... no great sense for analogue technology / or even high frequency.

and here is the video where you can hear the motor spinning up: LINK

Q: do I have to ground the Tx audio-in signal ?

Any help greatly appreciated.

Here's the picture of the cut wire:

post-5-1191278892_thumb.jpg

Edited by relee

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Your system appears to have more than one problem. Now it is time to verify that the Tx is not susceptible to vibration too. As Kilrah suggested, tap it with something (I like to use a screwdriver handle).

Most of these Tx's need to have its metal sardine can lid soldered at each corner; A press fit is not good enough. Some folks tape them instead, but I prefer to solder them. On some Tx's that suffer from vibration induced noise, the issue is related to the components. There's no practical cure for those situations (other than choosing a better Tx).

Earlier you mentioned that the Tx/Camera used the same battery pack. If this is the same battery that is used to power the heli motors, then that will usually cause a lot of noise. A dedicated battery is normally needed for the A/V equipment.

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From the first post I assume the batteries are separated, and he even put a separate one for cam and TX. On this kind of heli you most likely use more than 3s too for propulsion.

Before I go on, is that 2nd clip supposed to show something bad? Looks perfect to me.

No need to ground the audio, at least I never had problems with that.

If there is indeed something more that isn't shown in the video, I'd remove the TX (I don't like that metal/metal contact with the alu plate) and rather put some foam inbetween. Maybe simply some double-sided adhesive foam to avoid the rigid mount the cable ties create.

Vibration looks to be low on the vid, but it can differ quite a lot depending on the rotor RPM too.

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Before I go on, is that 2nd clip supposed to show something bad? Looks perfect to me.

Ahh, I didn't see that link. I agree, the new sample video looks fine to me too.

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the new video has audio in it .... which by definition shouldn't be there :unsure: since the Audio line was CUT. I didn't wanted to bother you with another crappy video (noisy again) so I only put the sequence of the spin-up into the video, where you can listen to the spin up of the rotor :ph34r:

I'll also test the vibration thing .... with the cheap Cam incl. Tx I used a sticky foam (since I couldn't get the screws in) ... excellent point, thanks

Any good explanation, why the video has audio in it, when there is no mic attached?

And yes, the main motor runs on 8s1p; Tx has it's own battery 2s1p (with 5.0 Volt regulator); Cam has it's own battery 3s1p; Tx electrical ground and Cam electrical ground are joined.

Edited by relee

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Any good explanation, why the video has audio in it, when there is no mic attached?

It is probably from the mechanical vibration. Is the small amount of ghost audio causing video problems? If it is, can you show us a new example of what it is doing?

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Thanks for your ongoing help with this .... I wouldn't knew where to turn otherwise.

To answer your question about the "ghost audio" I don't have any other proof. Only during spin-up and spin-down I can easily identify the audio signal - otherwise it's way to loud.

Here is a VIDEO during the flight today to show the video issues I'm facing with. The Tx / heli nose points towards 0 degrees (North), the diversity Rx is at about 110 degrees, Antenna is left of the heli ~ 270 degrees. So the antenna is right between the heli and the Rx.

What I don't like at all about the Tx is, that the "antenna" is hanging down left of the Tx. I tried a 2nd flight, where the antenna wouldn't be "blocked" by the heli .... and to have the antenna side-by-side of the Rx .... but still not too much luck with it VIDEO The heli nose is at 270 degrees, antenna at about 180 degrees, Rx @ 110.

My personal guess is, it's all related to:

1) the entenna not reaching out of the heli chassis (Gfk - no carbon)

2) high frequency vibrations towards the Tx - which I can fix address

I decided to use a metal blade to mount the Tx onto, due to it's heat .... but it can be easily changed.

Edited by relee

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Do me a favour and stick your tx to the bracket with some servo tape and no cable tie and see if it helps. can you also tell me what the board on the end of your aerial is ? maybe a picture of it if you can.

Terry

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can you also tell me what the board on the end of your aerial is ? maybe a picture of it if you can.

The antenna on that TX is this little PCB. The cable between is just a coax.

EDIT: Just watched the videos, stable static... starting to suspect ESC interference...

Edited by Kilrah

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The pcb is probably a bit directional which won't help matters.

Yes just watched the video too, strong electrical interference not mechanical.

Terry

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I could flip the setup - so that the antenna points downwards ... through a hole in the frame.

Can't I replace the antenna against a rubber duck?

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Yes you can use a rubber duck type and point it down.

Is there any chance that you interference is from an outside source ? wifi or phone ?

Terry

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@ Terry: no mobile phone / WiFi for the next 1000 meters

@ Mr. CR-Cam: can't I use a regular 8 USD SMA based rubber duck antenna?

no external interference - other than the heli - used exactly the same location / setup (Tx+Cam+Rx+Recording+Car+Shoes+Person) while doing a "walking" range check the day before :unsure:

so far implemented:

1) soldered every 4 corners of the Tx (sorry for the warranty)

2) orientation of the antenna is now towards the bottom

3) metal plate removed (cooking time's ahead - since the Tx get's quite warm)

4) mounted the Tx with a shock absorbing double sided sticky tape

AND YES - if someone has a recommendation for a good Tx (please less or equal than 100 mW, better less than 10 mW - please PM me)

post-5-1191280303_thumb.jpg

Edited by relee

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... can't I use a regular $8 USD SMA based rubber duck antenna

Sure, as long as you correctly install a mating SMA connector on the Tx.

BTW, the DiY rubber duck works the same as a $8 3dBi duck, yet will cost you nothing (you can use the existing coax). For improved performance, use the YB2normal ground plane design. This is a DiY site, so expect to receive DiY recommendations. :)

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@ Terry: no mobile phone / WiFi for the next 1000 meters

OK, we will asume no wifi or phone interference.

3) metal plate removed (cooking time's ahead - since the Tx get's quite warm)

100mW TX should not get very warm unless voltage too high.

All we can do is keep knocking the most likely causes off the list.

You can just use an 8USD aerial if you are happy you can connect it ok.

I think it's worth sorting the aerial before you go too much further with the fault diags. I will watch you videos again just to make sure Im not missing something.

Terry

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