Light Aircraft Association

Just a couple of quickies.

Does the PTT switch run from the jackplug to earth and is the switch one that conducts once pushed or one that is normally conductive until pushed?

Are the earths to the jackplugs (sockets) joined and then run to the airframe earth or are they earthed separately?

Ta.

The PTT switch has normally open contacts, conducts when pushed.

You should return you jackplug grounds to the ground terminal on your radio rather than the airframe ground. It is electrically the same, but less noise prone done that way.

(Ground = earth!!)

Frank Parker

Thanks, Frank.

I've got a switch in the box with the radio but it works back asswards. It may be that it is a handbrake switch from my Austin Healey. Certainly looks like a Lucas item and I may have put it in the radio parcel by mistake.

I'm getting there! I've found a friendly spanner who will sign my paperwork but he deals mostly in Boeing stuff. He wanted me to find out if a groundplane had to be flat or could it be the curved panel just ahead of the tail. If so, does it have to be earthed to the radio?

The PTT switch looks to be designed to earth to the earthing terminal of the jackplug socket (Sleeve, as in Tip-Ring-Sleeve) but there is no picture in the installation manual. It shows the earth running back into the radio via the sleeve terminal and a wire going back to the radio tray.

I can receive the Cardiff ATIS, ground and approach from 6 miles away. Is this good enough to proceed?

If you look at the transmit antenna on most spam cans you will see that they are mounted on the curved top of the fuselage, so I don't think you would have a problem with a curved ground plane in your installation. The gound plane is meant to provide an image of the antenna so that electrically it looks like a full dipole. Connect it to the outer of the coax feed at the antenna.

Frank Parker

......aaaaaand is there much current through the PTT wiring? Is it just enough current to trigger the electronic relay? I've got a tiny switch that will fit the column top but it takes very thin wiring of circa 1 amp.

Will be negligble current; probably just a few millamps.
Tony Nowak