Turn and bank interference

Clive · Post by **Clive** » Sun Jul 06, 2008 10:22 pm

I got the Esqual flying a couple of weeks back and one of the snags was the radio interference.
I improved the cable run off the dipole which made things better but finally discovered most of the problem is from the old fashioned electric turn and bank.
I picked up some hash from it when the panel was on test in the workshop and screened the supply and that improved things somewhat. The addition of the engine running has excited the whole thing and it's not acceptable, disconnect the T+B and all is OK.
I have the radio on a supply smoother and the headset/mic leads are all isolated and screened.
Same set up that the Jab has and it's a really sweet radio.

Ideas/comments, thanks Clive

C Rule · Post by **C Rule** » Sun Jul 06, 2008 10:41 pm

Have you tried passing the power lead to the T&S through some ferrite beads keeping them as close to the case of the instrument as possible?

Clive · Post by **Clive** » Mon Jul 07, 2008 5:41 pm

Any particular type of bead?

I've heard of these used before but have never tried them.

Ta, Clive

Steve Brown · Post by **Steve Brown** » Mon Jul 07, 2008 11:04 pm

A capacitor connected between live & earth feeds to the T&B?

C Rule · Post by **C Rule** » Tue Jul 08, 2008 7:12 pm

I think as to the type of bead it's a case of trial and error. or you could try and make a choke (inductance) by wrapping the power lead around a ferrite ring .Try experimenting with the number of turns. This coupled with the capacitor should produce a filter to take out the relevant rf energy

Clive · Post by **Clive** » Wed Jul 09, 2008 7:02 pm

I have the radio on an inductive choke smoother so the interference isn't coming up the power lead into the radio, I think it's radiating back down the supply from the T+B and then getting picked up as RF though the radio aerial. Is that possible?

CJ

mike newall · Post by **mike newall** » Wed Jul 09, 2008 11:23 pm

Wow - just the same problem that I have been chasing on my Citabia for a while.

Keep the suggestions coming - what type of capacitor please.

Mike Cross · Post by **Mike Cross** » Thu Jul 10, 2008 12:23 am

If any of you want ferrite beads drop me a PM with your address and Il'll be happy to post you a couple. I end up with plenty spare at work. They are designed to simply clip onto the wire. Form a loop in the wire and clip on to it so the wire passes through the bead and then loops round and goes though again. I recommend a nylon tie-wrap round it to ensure it doesn't come loose and it will be a good idea to tie wrap it to a support so its weight is not dangling on the wire.

Steve Brown · Post by **Steve Brown** » Thu Jul 10, 2008 11:38 am

A 0.1 microfarad ceramic capacitor (say a BX03D from Maplin) should help suppress the arcing in the motor which is possibly the source of the radio frequency noise. Doesn't matter which way round you connect it.

Frank Parker · Post by **Frank Parker** » Thu Jul 10, 2008 2:13 pm

I am sure that an EMI filter would help, but if the noise is that much of a problem it sounds as if the T&B is on it's way out and should go in for an overhaul.

Rob Swain · Post by **Rob Swain** » Thu Jul 10, 2008 3:51 pm

How about a new Turn & Slip/Bank/Co-ordinator?
Or get the existing one serviced?
Or have a hunt on eBay and the small ads for a replacement.

Not the cheapest options, granted, but if the gyro's motor is that noisy then I'd always wonder how long it will go for anyway.

I'm not just being flippant. In the past I've avoided expenditure and made do only to finally give in. Almost always I've thought afterwards, "why didn't I do this ages ago"!

Clive · Post by **Clive** » Fri Jul 11, 2008 9:22 pm

The T+B is new but was noisy the first time I powered it up. Got it from Light Aero.

The lads on the Jabiru owners have come up with similar suggestions, from Ralf:

If the T/B has a DC brush type motor a good way to reduce noise is fit a diode across the terminals for reverse shunt ie. the cathode (stripe) of diode to +ve terminal.

Diode can be 1N4004 thru 7 series. Adding a 0.1 capacitor across as well will finish the job.

I got this info from an IEEE publication in the 70s and it has worked for me on several generations of vehicles including electric radiator fans and fuel pumps. Can't be used on reversible motors (except ahead of the switch).

Ralph
-------------------------------------

I have an EMI fitted to the radio + intercom supply. Thanks for the offer Mike, I just ordered some beads and a capacitor from Paul at partsforaircraft (cheap and arrived 18hrs later).
I'm still at work till middle of next week but will report back on progress as soon as I get home and start soldering.

Thanks again, Regards, Clive

Frank Parker · Post by **Frank Parker** » Sat Jul 12, 2008 5:49 pm

If this is a new T&B which is producing EMI, then you should contact the vendor and the manufacturer and notify them of the product defect. I am sure that neither of them want to sell a product that is unsatisfactory. EMI generation would not normally be tested in a production environment, but it should have been tested to be EMI compliant when the part was certified.

For the benefit of the rest of us, what make is this instrument?

mike newall · Post by **mike newall** » Sun Jul 13, 2008 4:19 pm

Lucky guess here - it's a Falcon T & B........ ?

They are a reasonable unit, but I wonder if the quality control in China is good enough to cover RF emissions ?

Same problem in one of my aeroplanes - I am now going to investigate further

Clive · Post by **Clive** » Mon Jul 14, 2008 9:34 pm

Yep, it's a cheap Falcon import. I bought it 3 years ago so no joy with the supplier. I've spoken to light aero about another instrument out the batch and it was too long ago, and I can't say I blame them.

With these chinese things I think yer takes yer chance, I've been lucky in the past, a guy in the hanagr had three from Harry and they all had to go back. This was within the first year so Harry did the right thing. another guy's died the other week so I've had it apart and squirted some 3 in 1 in and it's up and running now.

Home in 2 days so will see, might stick it on a separate battery and let it run for 24 hours before I wire it in with all its jewelry.

Ta, Clive

Light Aircraft Association

Turn and bank interference

Turn and bank interference

Ferrite beads?

Choke

It's new!

Falcon indeed