Radio - Delcom 960

[Sean]

Hi. I have a Delcom 960 panel mounted radio in an aircraft I just purchased. I don't have any headset audio or side tone and I am not sure about the PTT wiring and there is a "home made" heaset box with a "modulator" adjustment and it all interfaces back to the radio via the MIC & SPEAKER connections. Can anyone give me some info on the set and how it should be wired?

 

Also, the aircraft is fabric covered, do I need to put a ground plane surface under the antenna base? It is currently mounted on a small plate attached to one the metal cross bars.

 

Thanks.

 

Sean.

 

 

[jetboy]

Sean,

 

The Delcom mic input is like most handhelds of the era, Icom A2 etc. expect to 'see' an electret microphone capsule connected there and the ptt goes live when the mic is present.

 

If you are using GA headsets they have an inbuilt amplifier that 'looks' like a carbon mic in terms of power requirement and audio level.

 

A simple way to connect these is by running 12v power via 1 Kohm resistor to the GA mic socket, and 0.1 uF capacitor from there to the Delcom mic input. From there connect 4.7 Kohm resistor to aircraft ptt line, other side of ptt goes to ground. If the modulation level is too high, connecting a resistor in line with the capacitor, value between 4.7 Kohm and 47 Kohm should help.

 

its likely the existing wiring does this.

 

If you have an intercom, it will probably have better provision for the radio.

 

Ralph

 

 

[Sean]

Hi Ralph.

 

Thank you so much.

 

The headset box is what you have mentioned.

 

The problem was the wiring between the box and the set but all is fixed now.

 

What are your thoughts on the ground plane or is the metal frame enough for a fabric covered aircraft?

 

Take care.

 

Sean.

 

 

[jetboy]

The small plate if bolted/riveted to the metal frame should be sufficient. can really only be checked with a reflectometer (swr) and from then on its a whole black art of adjusting cable lengths etc. so only worry about this if you have transmission troubles.

 

Ralph

 

 

[Sean]

I appreciate your help, thanks.

 

Sean.

 

 

[Sean]

RX probs

 

Hi again.

 

Well, the Delcom 920 radio works great with the engine off. Both Tx & Rx are crystal clear via the headset.

 

But with engine started the Tx is great - radio checks say it 4's. But the Rx audio is distorted (you can hear them but they are garbled or scratchy) most of the time, it sort of comes and goes. Also, with engine started the you can not adjust the squelch to make noise.

 

I have tried a RFI filter without any luck.

 

The unit is panel mounted in the dash and instrument/engine wiring is very close by. And we are running a 4A Power Mate off a Rotax 447

 

Any suggestions?

 

BTW: the aircraft (Supa Pup) flew for the first time on Sunday since we purchased it back in August. It was nice to see her up where she belongs.

 

Ta.

 

Sean.

 

 

[jetboy]

To find out if its DC power affecting the radio try running it just on battery and see if the noise is gone. The Powermate is a good regulator so should be OK.

 

If the noise is coming in the aerial things get a lot harder to fix, may need to put aerial under a wingtip or somewhere far away from the ignition side of the 447

 

Ralph

 

 

[Sean]

Cheers, thanks again.

 

Sean.