Headset Squeal

[djpacro]

Good cue for my question, please Michael.

 

Narco COM 810 in a rag & tube aeroplane with the antenna on a ground plane on top of fuselage (interesting article about antennae on your website). Some headsets work fine and others squeal when transmitting. I have one headset which squeals on 118.1 but fine on 123.00.

 

I clean the plugs frequently but even then normally get some interference on 118.1 however often much better on return to the field later.

 

Friend with an Airtourer has a similar problem - his consistently prefers headsets with the silver looking plugs.

 

 

[Guest Michael Coates]

Re: Radio Issues...

 

Very simple answer... not all headsets are created equal !

 

Headsets need to have a nice shield covering all the cables inside, this shield stops RF feedback getting into wires and squeeling.

 

A simple test is to press the PTT with the headset on your head but outside the aircraft and move around (as much as the lead will let you) and the squeeling will change, this PROVES RF is getting in.

 

To fix the problem is a little harder... Get better headsets or fit some Ferrite Cores... if someone could tell me how to post pics that would be good. The Ferrite Cores will help cut down the RF.

 

You will see Ferrite Cores on just about every cable in your house like the telephone cables, Cables on your computer screen, video camera etc... they are the small hard round blobs on the ends of the cables just up from the plug.

 

 

[Guest Glenn]

Re: Radio Issues...

 

if someone could tell me how to post pics that would be good.

Use imageshack to host your pics or our manage attachment section to attach your images. You can find these options below where you reply to messages :)

 

 

[djpacro]

Re: Radio Issues...

 

Thanks Michael, hadn't heard any of that from others I've asked.

 

Headset is a DC H10-40 which is 20 years old now.

 

With Xmas coming, maybe Santa will fix it - I see the ones on your website, how do you think one of those would go?

 

 

[Guest Michael Coates]

Re: Radio Issues...

 

I would bet money your cords are simply worn out from years of abuse, sorry i mean use.

 

If you flex the cables at the plugs by pulling the cable instead of the plug when you take them from the plane you will wreck the shielding really quickly and thats your problem.

 

Find a new name brand headset and try it instead.

 

IMO David Clarkes are always the best to use for checking planes (but they must be good (new - not 20 years old)).

 

If it works there will be a picture of a ferrite bead / core in a photo. You can buy these from Dick Smith/Jaycar etc... i have better photos at work to show you tomorrow.

 

 

 

[Guest Michael Coates]

Re: Radio Issues...

 

A ferrite bead is a passive electric component used to suppress high frequency noise in electronic circuits.

 

Ferrite beads employ the mechanism of high dissipation of high frequency currents in a ferrite to build high frequency noise suppression devices. Ferrite beads may also be called ferrite cores, ferrite rings, ferrite EMI filters, or mistakenly as ferrous beads.

 

Ferrite beads are similar to inductors in some ways but work especially in an area that is parasitic for general purpose inductors. They essentially act as a high impedance, or "resistor" to high frequency EMI/RFI electronic noise. The absorbed energy is converted to heat and dissipated by the ferrite, but only in extreme cases will the heat be noticeable.

 

Ferrite beads are one of the simplest and least expensive types of interference filters to install on preexisting electronic cabling.

 

For a simple ferrite ring, the wire is simply wrapped around the core through the center typically 5 or 7 times.

 

Clamp-on cores are also available, which can be attached without wrapping the wire at all.

 

Courtesy of the internet.

 

 

[Guest OzChris]

Re: Radio Issues...

 

More great posts and advise!

 

Im going to get me some of those from Dick Smith :]

 

At 'certain' RPM I am getting a bit of a *squeal* in my headsets and it changes as I move my head or play with the cords...Im thinking it is the same deal.

 

 

[Guest Michael Coates]

Re: Radio Issues...

 

Here is the picture i promised

 

 

[Guest Michael Coates]

Re: Radio Issues...

 

try again

 

 

[Guest Michael Coates]

Re: Radio Issues...

 

and again

 

 

 

[djpacro]

Re: Radio Issues...

 

Yes, others fly the aeroplane and they have new headsets which seem to work fine. Just myself and one or two others have problems.

 

I have one headset which works fine in the rear but squeals 100% when transmitting from the front.

 

Guess its time to buy a new headset and I'm inclined towards Michael's specials. Just one question - why gold-plating on the plugs?

 

 

[djpacro]

Well, I bought a new headset and it also squeals when transmitting on frequencies 118.1, 119.1 and 119.9. Fine on 123.0 and 135.7 etc.

 

Fine in the rear seat and fine in other aeroplanes.

 

i.e. same behaviour as the good one of my old DC's.

 

Flew with someone else in the front seat - his Bose worked fine as do many other headsets. Other people have headsets which squeal like mine.

 

Experts had previously replaced the antenna cable. They had also replaced the radio with same model NARCO COM 810 (that's a separate story but didn't really affect the squeals).

 

Local radio expert mutetred something about old tube and fabric aeroplanes with modern radios.

 

http://www.aerialpursuits.com/comms/commsfaq.htm has some other ideas:

 

- yes, intercom box is mounted right below the radio

 

Don't know about the other factors except the power supply - squeals seem less at the end of a flight so after the batetry has had more charge.

 

Only other info worth mentioning is that the antenna itself is old, maybe 30 years.

 

 

[Guest OzChris]

Did you try the Ferrite Beads that Michael was talking about?

 

I got them for my headsets that I use in the Thruster and the squeal has gone :]

 

 

[djpacro]

Thanks for the reminder, OzChris. Seems to work - will investigate further.

 

 

[djpacro]

Managed to get flying today with a headset that is normally unusable in the front seat. Worked 100% with the ferrite core. For info, a simple story on the subject at http://www.mglavionics.co.za/Docs/EMI%20suppressor%20for%20VHF%20frequencies.pdf

 

 

[Guest Michael Coates]

Good news.... a simple , cheap and easy fix !