Radio interference Scone CTAF 128.0

[Ascend Charlie]

Is 128.0 a frequency that just picks up interference from your own aircraft? You don't need to be in Scone to do this check for me...

I realise that very few of you have needed to dial up 128.0 since the frequency change, but has anybody found that some part of your aircraft's equipment causes reception interference on 128.0?

**** CAN YOU PLEASE just dial up 128.0 on your radios, when everything is up and running, and see if any reception noise is heard? You don't have to be at Scone for this test to work.****

Three of our machines, all completely different, have such interference. One we have tracked to the inverters - which can't be turned off to stop the interference.

One we tracked to the EFIS screens - which can't be turned off.

One is yet to be tracked.

A call to CASA and to AirServices resulted in the statement that "it just cost us a lot to change this frequency, and we won't change it again for one operator. You fix your aircraft."

Another response was "It went to the RAPAC meeting and it was passed." Well, of course there was no problem at that time, it is only after pilots have to select the new freq and use it that anybody detects a problem.

So, if anybody else out there has this problem, please speak up. This is also on the Rotorheads forum - sorry for any duplication, but I need some more affected people before AsA will act.

[Horatio Leafblower]

Had interference yesterday in a C172 - no EFIS screens in that. Have also had it in the Guzzle.

Why did they change it anyway? Interference with ML CEN around Cooma?

[CaptainMidnight]

Sorry Ascend Charlie but if Airservices, other authorities & operating agencies changed frequencies every time someone had a spurii caused by their own equipment then they'd be doing it regularly. And it does cost $$$$, aside from Airservices costs and re-licensing, it usually involves local authorities having to change their equipment as well eg. groundsman, Shire, firies, refueller etc. 128.0 is used at a number of CTAFs - should they all be changed as well??

Does the spurii completely knock out communications with other aircraft within the CTAF (if it does you've got a serious problem), or is it just annoying? If it is just the latter, then unfortunately you've either got to put up with it or get the problem fixed.

These things are not usually isolated i.e. you're probably not the only one in the world to suffer from interference caused by a particular device in your aircraft. Therefore the manufacturer of that device probably knows about the problem and has a fix. If they don't, then it could be symptomatic of a more serious problem which, if not fixed might suddenly let go and bite you in the worst possible circumstances. How's total EFIS failure at night on an instrument approach in the soup strike you, and possibly causing a C/B or two to trip at the same time? :ooh:

Get your avionics tech to make the calls & emails and chase down the problem.

[Ascend Charlie]

The only frequency i have heard noise on so far is 128.0

On Friday, in the middle of a pelting rainstorm, I was approaching Scone and made the normal CTAF calls. Despite the screeching electrical noise, I kept the volume up to listen for traffic, as the vis was pretty poor. On finals for runway 28, I see a lightie taxying up the runway ahead of me.

Not a problem, I am a chopper and can slow down to wait for him to taxy off to the hardstand, but i heard nothing from him. I shut down, and in the wind and rain at the bowser, ask him if he heard me : "Yes, and I talked back to you." I informed him that soon a jet would be arriving. I already knew that the jet had interference on 128.0 from their inverters.

He finishes his refuel, and taxies back onto the runway to head back for the threshold 28 and his hangar nearby. At this stage, the jet emerges from the gloop pointed straight at him. By pre-arangement they had 123.45 on the other set and I told them on a hand-held of the lightie, and that the wind favoured 11. They made a circuit and the runway was eventually clear for landing.

In the worst of circumstances, the situation could have been disastrous - the lightie could have been airborne heading at me, or the wind may have favoured the jet landing on 28 with the lightie still taxying in the rain. But airmanship and good fortune led to a safe result.

All I am asking is for people to simply tune up the freq and see if their aircraft, too, picks up some stray signal from its own circuits.

A simple aircraft, with no fancy electronics, probably will not be affected. If you have some swept-up gear, it might be an eye-opener. Enough numbers, AsA might look at avoiding that frequency.

At Scone, the ancillary cost would be zero, with no ground-based radio facilities. Sure, the ERSA and Notams will cost, but a lot less than a prang.

[pullock]

You are in need of a good radio LAME. Not one who woeld make faxes or phone calls to get the job done - one who has the knowledge and experience to fix your problems.

If the problem is as bad as you say, then you should get it fixed before further flight.

Got a scanner? Try it in your aircraft and see whether it's effected with the aircraft power on and off to eliminate local interferance or aircraft problems. If the problem is in your aircraft it's time to get a radio LAME. Carrying out fault finding yourself constitutes a maintenance task, and will require an appropriately licensed engineer.

:ok:

[Horatio Leafblower]

Several members of the Aero Club have scanners on when they are at work or at home and they also report that there are bursts of static from time to time on the frequency.

These static bursts did not occur on the old frequency of 118.8...:mad:

[Not_Another_Pot]

For me its 124.8, 430 screen makes one hell of a racket on both radios.

NAP

[Ascend Charlie]

Pullock:

Thanks for the reply - we know where the problem lies. In one bird, it is the EFIS screens. In another, the inverters. The third, we haven't tracked yet.

But what I REALLY want is for Prooners to test their own aircraft they fly, and report back here, e.g. R22, no noise (expected); B212, inverter noise; and so on.

[The Hedge]

Charlie,

Maybe a report to the ATSB about said incident would get something done.

Online Incident report form (http://www.atsb.gov.au/aviation/m3vco6t/notiffrm.cfm)

[Atlas Shrugged]

Overflew yesterday at A080 around 0800 and again at 1630 local and no interference on either radio - TB20GT. Tried 128.0 on the ground at Narrabri after shutdown just out of curiosity and again, nothing. Tried it again at BK on the ground last night and still nothing.

:confused:

A

[buckshot1777]

Several members of the Aero Club have scanners on when they are at work or at home and they also report that there are bursts of static from time to time on the frequency At work or at home?? That suggests something is causing widespread interference in the area, hopefully not the aircraft involved :D

In that case, interference location is the role of the Australian Communications Authority via one of the forms here (http://www.aca.gov.au/aca_home/publications/reports/forms/index.htm#interference) depending on whether or not you operate under a licence. They are who CASA ATSB and Airservices normally refer interference complaints to.

[trackdirect]

AC,
You should talk to your boss, I think he has a bit of pull in this country and I'm sure he doesnt want himself or any of his planes damaged with him in them.... If it costs a bit I am sure he has a few spare bucks lying around!!!:ok: ;)

[Zulu_One]

AC

Never heard of Scone, but there's a similar issue up in the Nth Kimberley CTAF 128.00 bashin round in 210s ...

Changing com's (if they worked) did the trick. No idea what the cause was though. Once radioed another a/c in the area when it was particularly bad and they said they had no problem ...

my 2 bob

Z1

[Matt-YSBK]

the 15th harmonic of 8Mhz is 128.0Mhz heaps of microprocessors have 8Mhz or dirivitive clocks. almost everything has a microprocessor in it today (even your digital watch).


Just a thought.

[pullock]

Can you tell me what kind of radios are being effected - are they all the same type of radio? If so, check it's mod status - especially if they are VHF 20's

If there is local interferance then what others have said is right, it's a job for the ACA, however if it's being caused by other aircraft equipment then you just need a radio tech.

I don't know what aircraft you have, putting 2 & 2 together I am guessing it's S76's. It's quite possible that ageing avionics in each might be getting dodgy capacitors and therefore creating spurious emissions. This being the case, it would have only been a matter of time until you became aware of the problem. Another problem could well be antenna bonding - is the problem worse in the wet?

On the aircraft with the EFIS displays making the noise, have you tried tracking it to a single display, or all at once?

[Horatio Leafblower]

Thanks Pullock

1979 Cessna C172K with C30 Nav/Comms

1996 Skyfox gazelle wit Icom i200 Comms

[YCKT]

Ascend Charlie

If it is the EFIS you need to put slugs on the power supply cables. I actually doubt it is the EFIS though, I think they are just a symptom.

Radio Frequencies mix up via a thing called intermodulation. This happens in the front end of the radio receiver. For example if you have a 104 MHz FM station nearby and a 24 MHz transmitter of any type close by the FIRST ORDER intermod is 128 MHz. (This is a very simplistic example and is most probably NOT what is happening to you).

A similar thing hapens in Canberra with a 104.7 MHz FM transmitter, the VOR and the 124.5 MHz approach. This is a much more complex third order intermod, but with old radios, all you can hear when flying over the VOR is 'benale' FM radio music.

Airservices know of this, I am not sure of the cost argument though, I personally think their design area can't cope with the homework and maths needed to avoid this sort of problem.

PM me, I'll have a look around Scone and run the numbers for you, do this BEFORE you spend $$$$$$ getting a radio LAME to fix what (s)he won't understand anyway.

[Ascend Charlie]

Atlas:

I have said several times on this thread:

The interference is internal to some aircraft, not coming from an external source.

Thanks for trying it out for me, it looks like some machines get it, others don't.

I have PMed some others for more details.

Anybody else who wishes to try it out, please make sure you have everything running, radars, EFIS or whatever, before you dial it up.

Thanx to all for your assistance.

[Richo]

AC

I have seen a similar thing to this before in the Torres Strait. The company had a C208 Grand which had loud constant static when ever operating on the CTAF freq.

The problem turned out to be the Shadin Trend Monitoring gear. A 24 pin data cable ran from the data key recorder to the CPU on the other side of the cockpit. This took it between the two VHF comms.

A LAME fixed the problem by installing a signal soaking block of some description around the data cable. I don't know the tech side of how, but it worked very well and we had no further problems.

Maybe your problem is similar and may be able to use the same fix. Check with your LAME or RAdio tech.

Richo

[pullock]

YCKT - if you knew anything about radio or aircraft you would know that the first tool you need to use is your ears. The fault description already eliminated your speil of drivvle. FWIW in my 13 years as a radio LAME I have NEVER encountered an intermod problem - why ? because they arent at all common unless the two signals and the receiver are colocated (meaning the signal strengths are VERY high (i knew you would need that explained:yuk: ). There aren't many colocated radio transmitters in the sky, and all aircraft equipment is specifically designed to NOT cause interferance to other aircraft equipment - if it does, it may not be fitted to the aircraft.

Perhaps even if you are arrogant enough to believe that you know more than industry professionals, you should be smart enough to not display your ignorance.