Light Aircraft Association

I've just been testing out my new headset. I'm sure I wasn't getting Bzzzzzt noise over the radio with the pump on in previous tests, but maybe I'm getting forgetful in my old age?

Anyway, is there a good suggestion for taming the noise?

Does the 'ground plane' of the aerial have to be earthed to the same earth as the radio? Wooden airframe, you see.

No Rob, unless you have your ground plane next to your radio it is best to have a separate earth for your radio, in fact, if you can 'isolate' your radio supply from your main bus-bar the better. That will cut out out the majority of your interference, you may still need RF chokes to clear the residual buzzing completely. It is quite a regular feature on some of aircraft, but I would double check the connectivity of your ground plane as well, just make sure the antenna base is firm and not susceptible to vibration and working itself loose, same with the fuel pump - check the earth (they shouldn't really interfere too much as they are quite simplistic in design).

Andy

So, would I be best advised to rewire the radio with braided cable sleeving on every wire and to ground them at one end? Is it the stuff that LAS sell?
http://www.lasaero.com/site/products/ar ... =N04EI2CCT
...or is there a supply of suitable wire with the sleeve already on it? I'd used modern thinwall automotive PVC cable since that was what was left on the stubs of the radio rack loom when I got the radio.

Has anyone got a supply of suitable 'stuff' for sale so that I can wire up the radio and a PTT on the stick assembly?

Also, is there a website with good info on wiring aircraft? I assume that wiring braid sleeve should only be earthed at one end?

Rob try www.aeroelectric.com Bob Nuckolls sells a book The AeroElectric Connection explains theory & practice in wiring your aircraft.
This is from the states but a download version may be available.

You may also sign up on the AeroElectric List to ask question or use archives go to http://www.matronics.com/Navigator? and select the lists you want.

Clive

I've bought some wire (shielded) and a roll of braid.
Am I right in saying that I only need to earth the comms wires at the radio end? If so, is it just the PTT, ear and mic wires or do I also need to do the power wires to the radio box.
Does the 'source' of RF noise (ie the fuel pump) need to also have shielding round the wires. If so, does it need shielding earthed on BOTH ends rather than the audio wires which are earthed solely on the radio end of the wire runs. Will earthing the body of the fuel pump help?

Not much specific info on the internet and a few bits are contradictory.

Best practice is to earth the screened wires at one end only (this avoids ground loops).
Best to use screened wire for PTT, ear and mic wires. Unlikely you will need to shield the pwr wire to your radio.
Try grounding the body of your pump first before looking at changing the pump wiring.
TN

I had a call today from a lecturer at Barry College. PTT doesn't need shielding (only signals onn-off rather than carrying info), the radio rack should be earthed to the comms bus, the comms bus needs to be earted separatelt to the battery via a large wire of the same size as the comms power-in, there might be a need for a 1 microfarad capacitor on the power line (a what?) and the fuel pump wires ought not to need anything. He suggests twisting wires together except for main power and earth feeds which need to be out of the way as much as possible. He also suggested that if the radio aerial has been cut "for 127Mhz" (as I think it was, John?) than it is unlikely to ever get near 3.0 units on the magical SWVR meter, or whatever it is called.

What your lecturer said all makes sense. The capacitor will get rid of any noise/electrical spikes that may be on the power wires. I would leave that for the very last action (capacitors are available from Maplin for a few pennies).

Tony

Hi Rob! Yes it was me and I will add a note of gloom I had similar just before my pump gave up!!! It was struggling to raise the fuel pressure and then I got the noise of a running pump but no fuel! One possible thought is there maybe a very fine filter on the tank side and if it is blocked it will increase the load (electrically) on the pump. It is screwed into the pump and looks like a brass coloured extension.
Regards John.

Still got that engine, John?

Anyway, I looked into installing 2 of those pumps in parallel but it seems they would also need NRVs in with them. I'm hoping that gravity + one pump will suffice since they are alleged to be capable of utilising up to 50% bio-fuel before the viton seals start to suffer. The UK suppliers (Glencoe) have some knowlegeable tech guys working there.

I've rewired the radio loom and there is less than an inch of exposed unshielded wire at each end (What an 'orrible job that was!) and I've used the casing of the radio rack as my ground since it seems to have been internally wired that way. I was advised to twist-n-solder wires, rather than crimping them together, and have added lots of heatshrink. Hopefully I can test it out tomorrow.

Sadly I bu66ered thetailspring up by getting the local headmaster to sit in FRED whilst I had him along for a bring-your-aeroplane-to-school day. Looks like it had never been heat-treated properly.



I've also got pics of the 100+ kids all waiting in turn to have a sit in FRED and to press the button for the machine-guns (PTT switch). The boys (ages 4 to 9) were mostly disappointed that the headmaster had made me remove the machine-guns and bombs. Sadly, I was informed that I need a special release form before I can utilise any photos of kids. What a world we live in!

Right-ho. The noise goes almost completely away if the Bose X headset is used with the anti-noise on (Wow! What a headset!). I've tried it with a standard headset and there is still about 10% of the ratatatat noise from the pump plus some wvvvvvvzzzzz from the alternator. I can hear Cardiff tower from 8.5 miles away when on the ground at Charlotte Church International airstrip but they can't hear me. So, how do I actually wire in one of these microfarad things? Is there an 'approved' source?

Next will be changing the tailskid pad for a wider one. The current one which came in a box with the aeroplane is a flat square of steel that seems to dig into the grass quite badly. Full rudder wasn't having much affect on the steering even with half revs and a little nudge from the stick.

PS The cows had a wonderful time watching me.

You don't need an "approved" source of capacitors (in aviation terms anyway).

The 1 microfarad capacitor will probably be a small cylindrical looking thing with a bare wire at each end. One end of the capacitor will be marked with a "+". This end needs to be connected to the +12V power lead to your pump. The other lead of the capacitor needs to go to a ground point or ground wire of your pump. Make sure you get the capacitor connected the right way round.

I am surprised the Bose headset is so good at getting rid of electrical interference. I thought its clever electronics was only to get rid of external "audio noise" as picked up via the headset mic.
TN

It seems that capacitors are also rated by their voltage. Any suggestions as to which one I need (ie part number or supplier)?
I've a suspicion that the Regulator/Rectifier might be on the way out. At high rpm I was getting an overvolt warning signal though the Leburg. A quick check on the internet for "Regulator failure Honda CBR600" shows up a lot of known problems with this unit due to overheating and consequent over-volts, plus, it also lists suggested replacement with a suzuki GSXR one.

Tony. The Bose seems to work on reducing the alternator noise since it seems to have the buzz coinciding with the exhaust noise. It took me a while to work that one out. Anyway, it works remarkably well.

Rob
I had a regulator fry on my D9 and replaced it like for like with this
http://www.electrexworld.co.uk/rr58-reg ... 779-0.html. This lasted me a further few years until I sold the a/c. Only later did I hear recommendations about a suzuki alternative!