Light Aircraft Association

How do people connect screened leads together, such as when connecting up mic wiring between headsets, intercoms and radios etc?

Solder? Crimps of some kind?

I have always soldered the connections, but any reliable low impedance method of connection would be acceptable.
Noel.

Rob

It is usually possible to arrange your wiring so there are no connections, other than at the plugs and sockets themselves. That is to say, the best way of connecting screened cables is not to have any breaks in the first place.

Simon C
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It depends on the use of the wire, if its mic you dont have to worry too much about breaking the screen continuity and I would twist, solder and sleeve the inner keeping it screened as much as possible and the twist and solder the screen and overall sleeve or insulate.
If its an areial lead then any discontinuity of screen will upset the transmission characteristics and cause missmatch, losses, radiation and RF relections in the cable and you would be better off using an RF connector like a BMC free plug and socket. Particularly if its a TX cable.

Hi again Rob,

I have just done my first radio/intercom installation and was advised to ensure that all the screens come together at a single earth point which involved isolating the mic/phone sockets from the structure and bringing the screens all together at a brass terminal block at the business end which was a bit of a pain to organise. Actually, it took a couple of attempts to make a loom I was satisfied with.

The key thing is that only one end of a screen was earthed, not both ends. I can see the logic of that though as there could otherwise be a tiny current flowing in the screen. Sounds unlikely, but I was once a hi-fi buff!

Was the work necessary? All I can say is it worked well.

Colin

Rob,

Sometimes it is easier to solder a small "pig tail" wire to the screen and then use a crimp on the end of the pig tail. I would also recommend using heat shrink sleeving around the point the screening exits the outer insulation. Lastly, go carefully when soldering to the screen. Sometimes the heat can melt the inner insulation (obviously dependant on the type of wire you are using).

Tony Nowak

Bringing screens together at the input end is true for audio microphones so that the sensitive input is seeing only the differential. headset is not so critical as the signal is large and just going to the speaker and you are shielding other things from it. If you plug in a DC headset the screens and returns are all connected anyway.
Again though and RF has to be treated completely differently - dont go taking that off to a brass block.

I'm OK with the antenna cables - they don't have any connections other than a BNC at each end. Used to play with CB radios many years ago so I know the value of decent connections in this area!

The reason for joins is partly for connecting a Sigtronics intercom as part of the installation, and making an attempt at using this with 2 radios, which I am assured the SPA400 makes possible without the need for an audio panel. We shall see.

Heat shrink sleeve - where would we be without it, and not just for electrical type cables!

Thanks for all the responses - I'll shut up and get on with the job now!