RF issues on 35m

[john stones 1 - Moderator]

I have been using a JR 9x for10 years Terry, mostly 6v now using life 6.6v with PCM rx's never had an issue.

John

[Allan Bennett]

Posted by terry westrop on 16/11/2014 23:06:50:

... What is an 'opto isolator'.......?? ....

It's a device that electrically isolates two electronic circuits from each other. It consists of an LED and a light detector inside a single package, so the signal (throttle signal in the case of our ESCs) goes into the LED, crosses the gap in the form of light, and is re-formed into a signal by the detector.

With a regular ESC there's a continuous electrical connection between all components via the earth/ground wire, which can transmit interference from the motor and the switching parts of the ESC to the receiver. With an opto ESC this path is absent, so interference is reduced or eliminated. It does require the use of a separate receiver battery though, for if you were to use a stand-alone BEC you would be creating another direct ground path from battery to receiver, thus negating the opto advantage.

[Martyn K]

Hi Terry

I suspect that your problem my be due to close proximity coupling between the aerial and the servo leads. Is the aerial inside the fuselage or outside - traditional - clipped to the end of the fin?

Martyn

[Lee Smalley]

on 35 meg it is unlikely that the aerial is coupling onto anything as it is not actually transmitting anything it is probably having its signal "stolen" by the rf transmitted signal coupling onto the servos extensions, it is easy to check, remove extension leads and check range, if all is good until you re-install the servo extensions then try ferrite rings half way along the extension leads (loop them through 3 times) it may work it may not, rf testing is a bit of a black art im afraid

[terry westrop]

So the 'opto thingy' is on the esc lead Allan? I have disconnected the esc from the rx, no change. I do run a separate rx NiCad.

So 6v is ok....?? JR not know this then John.....?? Very strange! I've been giving my 6v nicads away on their advice! I do recall using single channel (1960's ) increasing voltage improved range. I would expect similar with today's RC...?

Hi Martyn from Classic aeros. I never thought to put this on that forum as I'd expect most would be using 'classic IC' I have tried the aerial outside to the fin top on ZPCM only. I have SPCM left to try.

Lee, you appear to 'nail it'....stolen range sounds spot on. Stolen/masked by the extension lead RF. Yes, removing ext leads cures the issues, which I've tried early on, (in the main on ZPCM). SPCM to try. I've tried the clip on ferrites on the ext leads, zero success. Are the round examples superior?

[Allan Bennett]

Posted by terry westrop on 17/11/2014 23:55:54:

So the 'opto thingy' is on the esc lead Allan? I have disconnected the esc from the rx, no change. I do run a separate rx NiCad. ...

The opto thingy is actually built into the ESC. You won't see any difference from outside, apart from "opto" on the label, unless you take the heatshrink off and know what you're looking for.

Some ESCs that aren't opto come without built-in BECs, and some Far Eastern suppliers have been known to mis-label them as "opto" -- either out of ignorance, or deliberately. If in doubt, a simple test is to disconnect the red wire from the plug that goes to the receiver. A true opto ESC will not function without that wire, for it needs power from the receiver to power half of the opto circuit. All other ESCs will function with that wire removed, provided you've given the receiver a suitable stand-alone supply.

[Martyn K]

Posted by Lee Smalley on 17/11/2014 17:06:47:

on 35 meg it is unlikely that the aerial is coupling onto anything as it is not actually transmitting anything it is probably having its signal "stolen" by the rf transmitted signal coupling onto the servos extensions, it is easy to check, remove extension leads and check range, if all is good until you re-install the servo extensions then try ferrite rings half way along the extension leads (loop them through 3 times) it may work it may not, rf testing is a bit of a black art im afraid

Hi Lee

I was referring to any noise in the long servo leads. The magnetic component of the RF field is relatively strong at close proximity and could possibly be coupling with the aerial lead if it is laid along side it. That is why we never lay data cables in parallel and close proximity with power cables. I agree though that the induced signal would be weak but it should be eliminated as part of the investigation.

There is a second possible effect, the long servo leads could actually detune the 35MHz aerial - again highly unlikely as these aerials are inductively loaded.

Martyn

[terry westrop]

Thank you Martyn & nice to find you on this forum also.

What sort of distance should the aerial/ext leads be placed apart? Are there any other 'types' of ext leads that could be employed to minimise this problem?

As I mentioned at the outset, a 'whip' aerial would almost certainly be optimum but I really don't wish to go there again.

Could be 2.4 otherwise I guess, but would be nice to sort the 35m situation. I do not leaving stuff unresolved.

Thanks again for all the help.

[Lee Smalley]

I have not really noticed any difference between ring and clip on ferrites with clip ons you do not have to loop them through as much, once or twice is usually sufficient, Martyn is correct you need to keep them apart as much as possible in case there is any noise from the extension leads being picked up by the aerial however again this with modern components is rare, RF testing is a black and not always a scientific art sometimes weird stuff works, try wrapping the extension leads in tin foil or carbon tape, you would be amazed at the stuff we have tried to stop our products being susceptible, we shortened 1 track on a PCB by a few mm once and hey presto, problem cured

[Chris Bott - Moderator]

Have you tried twisted extension cables yet Terry? They did cure one or two of my 35Mhz problems.

For example the description on the Puffin website includes these words "These heavy duty servo extension leads are twisted to reduce radio interference",

[Martyn K]

Hi Terry

My thoughts would be to route the aerial to the fin and put the servo leads as far away as possible. This may be a need to move the Rx aerial away from the servo leads by routing it forward from Rx then back to the fin. Just route the aerial as far away from potentially electrically noisy sources. Its not an easy task..

M

[Former Member]

[This posting has been removed]

[terry westrop]

Ext lead Length could be the cause in my case,(1m). I have previously been advised that twisted cables may work, thanks for the link Chris, I'd not been able to locate such previously. Expensive, old fashioned (my first set of Futaba had servos with twisted cables).

Dare I try 6v with my JR Rx.........?

[terry westrop]

Ext lead Length could be the cause in my case,(1m). I have previously been advised that twisted cables may work, thanks for the link Chris, I'd not been able to locate such previously. Expensive, old fashioned (my first set of Futaba had servos with twisted cables).

Dare I try 6v with my JR Rx.........?

[Chris Bott - Moderator]

Terry my first thought when you mentioned 6V was this - IF the interference is caused by switching transients in the servo extensions being picked up by the aerial, then going to 6V is very likely to make any current flowing in the extension leads bigger. In turn, the interference would then be worse, wouldn't it?

You watch though, 6V will fix the problem now.

[kc]

Twisted type extension leads are available from Component-Shop.co.uk in sizes up to 500mm. I think they may make up specials too. They supply the twisted servo wire by the metre in 22 or 20SWG and JR or futaba type plugs if you want to make your own. The twisted wire is available in Futaba colours or Hitec colours.

[roger graves]

Ihad prolems on 35meg the only cure I found was to change to Jeti rxs from Fubar and run the aerial out over the wing

[terry westrop]

Thank you again. I have now ordered the suggested twisted HD ext leads, safer than 6v trial initially. If the new leads improve things I'll try the 6v, just to compare.

I reckon aerial over the wing would be good, but not practical however. I'll hope the above works

I'll report back my final results

[stu knowles]

Another thought, I once had a SM services fail safe unit that caused me no end of glitch problems. Even Terry at SMS couldn't find out why although he accepted that it was the case when i sent the unit back to him. Same situation with an electronic air valve.... so any non standard components in the system??

Also had a series of incidents, interference, bad glitches etc that eventually was traced back to me changing my phone from 'just a phone' - which didn't affect my radio at all, to a smart phone which certainly did. Cost me a full service and a new TX to discover that 35mg doesn't like some smart phones!

The latter was what tipped the moved away from 35mg, even if I leave my phone in the car you never know if anyone standing by you has one in their pocket. I still use 35 mg in models I fly locally but anything likely to be flown at a fly in has 2.4

[terry westrop]

Thx Stu. I've no fancy devices fitted, simple RC/EP installation. Phone is well away, so cannot put blame there, but I've heard of 'blank memory' syndrome with 35 & mobiles however. Smart phones....that's a new one. How close did the phone need to be to the Tx?

[Allan Bennett]

Posted by stu knowles on 28/11/2014 23:24:47:

... Also had a series of incidents, interference, bad glitches etc that eventually was traced back to me changing my phone from 'just a phone' - which didn't affect my radio at all, to a smart phone which certainly did. Cost me a full service and a new TX to discover that 35mg doesn't like some smart phones! ...

I wonder if having WiFi and/or Bluetooth or near-field-communication enabled on ones smart phone causes the problem. Or even whether or not it's in 3G mode.

[IanN]

Posted by terry westrop on 15/11/2014 23:55:24:

What is a Loaded Dice doing in the loft....it was created to fly & inspire pilots to fly better. Which version might it be?

I also have to plead guilty on that score a Loaded Dice 40 kit in my case

Fascinating discussion...

[stu knowles]

Re the phone situation, The phone was kept in a hanger on my belt, so quite close. My old flip phone never showed any animosity to the radio at all. When I swopped to a new phone I never gave a thought to potential effects on the radio. (Yes I had seen the advice from the BMFA - can't blame anyone else but myself)

As a slightly connected point, all my RX's were Multiplex IPD. So good are they that they showed not a jot of interference...... right up to the point that they say, "Thats it! can't take any more" ... and go into failsafe. The F/S situation only lasts a second or two but in a low fly by it was enough to put one into the floor. Like you I swapped every component, sent by TX back to Mike Ridley and when that didn't provide a cure, I bought a new TX. Then one day I was working on a model in the shed and I could see that momentarily it went into F/S mode. It was just sat there, no engine running, not being touched. The flaps went right down (F/S mode) and then back up again. It happens at seemingly random and infrequent intervals but after discussing things with Mike Ridley, the phone was thrown up as the number one suspect. Since then I leave the phone in the car and have not had any further trouble. The phone does have Bluetooth, WiFi and all the rest but I have not tried to pin point the exact cause.

I did think that if I had been using less clever RX's the interference would have been less well masked and probably have made itself known sooner, which might have helped to track down the cause sooner.

Hope that you track down your Gremlins soon

[terry westrop]

That Loaded Dice 40 kit is very rare now as the Newmans stopped manufacturing long ago Ian.

I have both types of phone, but never have them on me whilst flying, not because of that mentioned above, but the Tx memory wipe out potential that has occurred previously with other users. (again JR)

I have now fitted 600mm twisted leads to one model, yet to be flown. The ground range seems not much improved however, so I'm not optimistic the problem will be solved.

[Allan Bennett]

I've just remembered, we have one phone mast on our field, and another within 1/4 mile, and we don't suffer any interference that we're aware of -- not even on 35MHz or 27MHz. So I doubt it's the phone signal per se, which is why I suggested it might be WiFi or Bluetooth, both of which can be disabled on modern smart phone.

Edited By Allan Bennett on 07/12/2014 09:01:23