Avionics - question about happenings.

[flying dog]

Ok, I have asked and been given AN explination, but in thinking about it: What was said doesn't quite work for me.

 

No offence to the person who said it.

 

Scenario:

 

Jab' with radio. My head set.

 

When in flight and I talk, it is distorted with a lot of background noise and "pulsing".

 

It was said this is called "motor boating" and it is because the altermeter is not big/strong enogh to handle the load. Sounds plausible.

 

But let's look at some things which I feel/think fail that idea:

 

I am flying, not idling. The revs are at about 2700, the voltage is 14.4 and there is little else on. IE: No landing lights, no NAV lights, no beacon, no strobes. Just the radio, Xponder, EFIS and HSI. Oh, ok, and my GPS plugged in the AUX socket.

 

Now, fair enough voltage and current are different things, but if the alternator wasn't cutting it, wouldn't the voltage also be fluctuating? And there is a battery in the equation to "fill in the gaps" if the alternator wasn't producing enough output.

 

Of course throughout this the CHARGE light is NOT glowing. It does at idle.

 

So who has any other ideas? Yes, I know that usually with that kind of problem the power supply is the first and major suspect. But given the voltage (inndicated) is 14.4 at the time, it sort of shoots that idea dead.

 

At idle, the voltage goes down to 11.9/what ever. I can clearly see that with revs/power the voltage increases, which makes sense.

 

Anyone?

 

 

[facthunter]

Your radio should operate from the battery by itself as long as it is charged. Can you turn off the alternator and all other electrics and see if the noise disappears, as you isolate all the possibilities? Nev

 

 

[flying dog]

Thanks, Nev. Shall try maybe one day. But it is a rental. So I can't just do these things at will.

 

Also don't know if the battery voltage is good enough.

 

I shall try it next time with engine not running and see what happens. I guess the only "trick" is getting someone to monitor me while parked. Then start engine and see if it makes any difference.

 

 

[skyfox1]

Have you tried switching off the GPS and other electronics to isolate any problems that they may be causing.

 

l had a similar problem and found my GPS was the problem .

 

 

[flying dog]

Skyfox,

 

Well no not yet.

 

It only started happening the other day.

 

I'll post updates, but was interested in people's thoughts on anything else which could be causing the problem.

 

 

[Guest Andys@coffs]

FD I dont understand the problem, supplimentary Questions Asked below:-

 

Ok, I have asked and been given AN explination, but in thinking about it: What was said doesn't quite work for me.No offence to the person who said it.

 

Scenario:

 

Jab' with radio. My head set.

 

When in flight and I talk, it is distorted with a lot of background noise and "pulsing".

 

Is this distortion in your earphones, or has it been reported by other stations that you are distorted on transmit? If the distortion is in your earphones, are others telling you the transmission is also distorted? Given that most headphones are connected to an intercom, is intercom functionality Ok, or have you only been one up? if a Jabiru have you used the PM501 Passenger Isolate switch (Middle switch on the intercom panel) to remove the passenger circuitry from Question?

 

It was said this is called "motor boating" and it is because the altermeter is not big/strong enogh to handle the load. Sounds plausible.

 

But let's look at some things which I feel/think fail that idea:

 

I am flying, not idling. The revs are at about 2700, the voltage is 14.4 How do you know this? if its a digital display ie in the radio menu, then it doesnt mean much alone. it could average (or more likely Root Mean Square) 14.4V but have 2-3 volts or ripple noise on the supply line (ie be constantly moving from say 12.9 v to 15.9v)..... and there is little else on. IE: No landing lights, no NAV lights, no beacon, no strobes. Just the radio, Xponder, EFIS and HSI. Oh, ok, and my GPS plugged in the AUX socket.

 

Now, fair enough voltage and current are different things, but if the alternator wasn't cutting it, wouldn't the voltage also be fluctuating? And there is a battery in the equation to "fill in the gaps" if the alternator wasn't producing enough output.

 

Of course throughout this the CHARGE light is NOT glowing. It does at idle. If the charge light is Off, and is on at idle (proving it works) then the simple reality is that the draw is not greater than the supply so in broad terms all good (of course things in life are rarely that simple, is it fully off, or is it just glowing dimly etc)

 

So who has any other ideas? Yes, I know that usually with that kind of problem the power supply is the first and major suspect. But given the voltage (inndicated) is 14.4 at the time, it sort of shoots that idea dead.

 

At idle, the voltage goes down to 11.9/what ever. I can clearly see that with revs/power the voltage increases, which makes sense.

 

Aircraft radios are notorious for suffering from RF Feedback in the headset lead. It works as a good antenna when only meters away from the transmit antenna. If the problem is present with your headset is it also present with other headsets of a different type? quick way to test for this is to buy a $3 computer cable ferrite at an electronics store (no not DSE, they are no longer an electronics store, just a Big W entertainment section....which must rankle Dick I would have guessed.....) put the ferrite as close to the plug end as possible and wrap the lead around it twice or 3 times before closing the ferrite. That will probably exclude RF injection in the headset leads as a source of problems.

 

Anyone?

[flying dog]

Andy,

 

Ok, I left my self open there.

 

The other stations are reporting the distortion. I can "squelsh out" any muck I hear from myself.

 

I am asking for Sydney QNH and need to ask more than once and Sydney radar are informing me of broken transmission with background noise.

 

There are no other headphones plugged in at the time and the intercom is also set to ISOLATE.

 

The voltage reading I am getting if from the Dynon EFIS.

 

 

[Guest Andys@coffs]

Ok... and to the question of headsets? is it only on your headset or, I pressume being the club jabby, others are also having the same issue? If just your headset try the ferrite thing I mentioned....You may find you already have one lying around somewhere.

 

So when on the ground, what do people tell you your Tx is like? both with motor on and off....

 

Andy

 

 

[flying dog]

Well, I have my headset. I don't like snogging everyone else who have flown the plane.

 

Ok, it is a cheapy, but it has worked on other Jab's - but that may not be saying much.

 

First time I have flown that one and transmitting when in the circuit (or turning base/final) with no revs, is basically pointless as the CHARGE light is glowing quite brightly and pusing the TX button bascailly the radio fails.

 

 

[Guest Andys@coffs]

Then there is something majorly wrong. The fact that the alternator isnt charging should not prevent the radio/headset working while the battery has a normal charge level (ie should be Ok for hours on battery alone. In fact would say that wehile ever the supply voltage at the radio is>11v then I'd be suprised if it didnt work without any issues).

 

Personally that is fantastic, it gives you a hard and fast fault to track down......assuming the same is true of the headsets that normally go with the plane.....

 

Andy

 

 

[flying dog]

Yeah,

 

I am not bagging the people who rent the plane. I shall have to try and find time myself to try and work out where/what the fault/problem is.

 

But as the plane is 1.6 hours away from me, it is not something I can do just any time.

 

 

[Guest davidh10]

I agree with Andy@Coffs. "motorboating", if that is what is happening, is RF feedback, likely due to poor shielding and or signal ground issues.

 

Couple the fact that there appears to be a supply voltage issue as well and it may be caused by a poor earth or battery feed path between the battery and the radio or even a battery that is in stages of internal decay.

 

I'd follow up on the battery voltage / charging issues first. After that is fixed, then re-test. Check if it happens with the normal headset that the aircraft owner uses. Isolate whether it is the headset, the radio or the combination. Depending on whether the signal ground for the headset is separate from the cord shield, it could even be a miswired plug / socket.

 

Try transmitting without a headset attached. Does it still "motorboat"?

 

It is probably difficult to fault find an aircraft that is being hired, but the owner must be made aware of the issue and your willingness to assist in troubleshooting.

 

 

[flying dog]

The term "motorboating" was used by another person to discribe the voltage dropping below usable while the unit it trying to transmit.

 

Maybe not the "accepted" meaning, but that is how he discribed it.

 

 

[sain]

check out a decent faq on aircraft radio noise and inteference and work out a checklist of things to try before you head up next time. It'd be really helpful to have somebody else up there with a radio so you can diagnose the problem. A second headset would be useful too.

 

This guide would be a pretty decent starting point: http://www.lightaircraftassociation.co.uk/engineering/TechnicalLeaflets/Mods%20and%20Repairs/TL%203.14%20Radio%20Interference.pdf.

 

Some of the others here with more knowledge than me may be able to help you work up a checklist of things to test so you can figure out whats happening.

 

 

[XAIRVTW]

Flying dog try measuring the voltage straight from the battery this will tell you what current is being supplied to the battery. I know you said your voltage you measured was from your Dynon my EFIS gave a stable voltage as well. What I am looking at is the voltage regulator the Kubota ones that Jabiru supply some of them do play up. I had a simillar problem put ferrite all long power cables & radio PT cables used shielded wires on the installation still had the problem I checked the regulator while doing some ground testing & was showing some abnormal spikes which it never did before. Replace regulator problem was solved might be worth a try you never know.

 

Cheers

 

 

[Virago]

Flying dog, this sounds to me like RF feedback (as mentioned by Andy@coffs). Some radios and headsets are more susceptible to it than others but the biggest factor is the distance (or lack of it) of the antenna from the headset. As the Jabiru is a GRP aircraft, there won't be the same degree of shielding that you would get with a metal aeroplane. Are the mic and phone jacks located behind your head? If so, this can make it even more susceptible. The wires to the jacks should be shielded and so should the headset cord. I have seen headset cords that were unshielded ... that's asking for it! As the aircraft is not yours, it will be difficult for you to experiment. Firstly, try a known good headset. Secondly, try your headset in another plane. In extreme cases, I have had to shift the antenna to the belly and install it with a sizeable ground plane. This usually fixes the problem in aircraft such as Tiger moths which also don't have much natural shielding. Good luck. John (retired avionics LAME).

 

 

[J170 Owner]

Ok, I have asked and been given AN explination, but in thinking about it: What was said doesn't quite work for me.No offence to the person who said it.

 

Scenario:

 

Jab' with radio. My head set.

 

When in flight and I talk, it is distorted with a lot of background noise and "pulsing".

 

It was said this is called "motor boating" and it is because the altermeter is not big/strong enogh to handle the load. Sounds plausible.

 

But let's look at some things which I feel/think fail that idea:

 

I am flying, not idling. The revs are at about 2700, the voltage is 14.4 and there is little else on. IE: No landing lights, no NAV lights, no beacon, no strobes. Just the radio, Xponder, EFIS and HSI. Oh, ok, and my GPS plugged in the AUX socket.

 

Now, fair enough voltage and current are different things, but if the alternator wasn't cutting it, wouldn't the voltage also be fluctuating? And there is a battery in the equation to "fill in the gaps" if the alternator wasn't producing enough output.

 

Of course throughout this the CHARGE light is NOT glowing. It does at idle.

 

So who has any other ideas? Yes, I know that usually with that kind of problem the power supply is the first and major suspect. But given the voltage (inndicated) is 14.4 at the time, it sort of shoots that idea dead.

 

At idle, the voltage goes down to 11.9/what ever. I can clearly see that with revs/power the voltage increases, which makes sense.

 

Anyone?

My microair M760 draws 1.8amps on transmit and will operate down to 10 volts. Check you are getting at least minimum voltage AT THE RADIO when transmitting. I think most Jabs come standard with M760 radios. Will think on this for you.

 

Kevin (Radio Tech from the 70s)

 

 

[flying dog]

Yeah, the radio is one of those small round things which are the "norm" for Jabs.

 

Alas a lot of testing will have to wait until next time I am down that part of the world - it is 1.5 hours driving - so it is not every day I am close to it.

 

 

[Virago]

Have someone check the connections to the circuit breaker. If they are loose, you would have a voltage drop across the breaker. I don't think it is a total aircraft power supply problem. I'm not familiar with the Microair radios but some VHF radios are prone to what is called "downward modulation" which may (or may not) be accompanied by RF feedback. That causes distortion and warbling on TX. If you are renting, you could simply refuse to rent that particular aircraft until the owner gets it fixed. RF feedback problems are rarely quick fixes. John.

 

 

[J170 Owner]

Could make an entry into the aircraft's logbook that the radio has a fault. Might make an enemy as well.

 

 

[jetjr]

Jabs have issues with ignition shielding AND I think the generator is always charging full power in flight. It doesnt cut in or out. It doesnt start until 1500rpm much but after that it should be on line and pushing out around 8 Amps. Your radio draws buggerall so doesnt sound like a charge system issue.

 

It could be aircraft issues or the radio needs a service - speak to a Avionics guy or Microair.

 

 

[Virago]

Where a defect exists, you have a right ... indeed an obligation, to make an entry in the aircraft's maintenance release. Describe the fault accurately and in detail. This will ensure the matter gets attended to in the appropriate way. Just make sure it's not your headset causing the problem by flying with the aircraft's own headset. Disinfect it first if you have to but it's essential you carry out this test. It is not unusual for a particular headset/radio/installation combination to result in RF feedback. John.

 

 

[techie49]

Hi FD,

 

It does sound like RF feedback. If the battery voltage is pushed up by the alternator, the output of the radio will be higher than on idle and may get into the headset. First change your headset as it's unlikely all the users of the aircraft will have experienced the problem and not said anything. If it isn't your headset why has it suddenly started? Again, others would surely have noticed the problem if it's the radio. I'd go for a problem with the antenna next but you'll need to test with a SWR meter to check that what's going up the aerial lead is actually being radiated and not coming back down the feeder. Be interested to know the cause if you find out.

 

Paul

 

 

[Spriteah]

Headset try and eliminate first. If not that and as it is not your plane refer to the owner. It's not your right to start mucking around with a rental as it must be maintained by a level 2 under the guidance of the owner or operator. Not the renter.

 

Cheers,

 

Jim

 

Austec Avionics.