Trig TY91 noise

Spare a thought for those of us still flying with a Narco radio :-)

Lucky you with the Narco. We loved our Russian Baklan radio, several kgs weight but great radio. But for the “new” registration no chance with it for 8,33 requirement. By the way, we have a loud noise in that Trig, but very clear transmissions. So I guess I messed up the wiring , suspecting intercom connections. Still some head scratching … Vic

My guess is that the tuning head is interfaced via some serial protocol (clock and data wires). It ought to be fairly obvious if one saw the cable connections between the two.

Then one could try the following:

• wire up the interconnection with a shielded cable (if not already done so) with the shield going back to the radio box/chassis
• put some suppression components onto the cable; an easy way would be to try clipping on some ferrites like these
• do some noise reduction (RC) on individual signals in the cable (won’t be authorised, of course, but…)

Trig have stated that the noise is coming from the link between the tuning head and the main body of the radio. They admit that. They have merely suggested a way of mitigating it, but not eliminating it.

What your saying is that these cables are radiating. They won’t be radiating when you have shielded them. You could always double shield them as well.
Really, this radio should be able to provide clear audio.

I always use shielded wiring for the TMAP bus as well. Did you use shielded wiring here (not required according the manual), it is in my opinion always a good idea to use shielded wiring on databusses and analog signals, so I must admit I never tried without.

What your saying is that these cables are radiating

Could be, or the remote unit could be generating a lot of RF which is conducted back into the radio.

After all, the radio should have a metal box, so if it is affected by a bit of radiation from a cable, it has little chance in an aircraft where you have some watts of VHF radiated just 1m-2m away.

Could be, or the remote unit could be generating a lot of RF which is conducted back into the radio. After all, the radio should have a metal box, so if it is affected by a bit of radiation from a cable, it has little chance in an aircraft where you have some watts of VHF radiated just 1m-2m away.

It is affected on the audio part. The databus isn’t affected now, and is far less likely to be sensitive to that, as the voltage levels are much higher then with the small audio signal. There is something wrong, this isn’t normal behaviour. From my personal experiance, having done quite some of these units, these really should work fine.

Peter wrote:

the tuning head is interfaced via some serial protocol (clock and data wires)

Actually differential asynchronous – there’s a data A wire and a data B wire and that’s all. They’re supposed to be symmetrical i.e. when one is high the other is low and v.v.
But no separate clock signal.

BTW my own initial install had close on a metre of unshielded copper wire between the radio body and the control unit and not a whisper of noise, not when flying but neither on the lab bench.

Actually differential asynchronous – there’s a data A wire and a data B wire and that’s all. They’re supposed to be symmetrical i.e. when one is high the other is low and v.v.
But no separate clock signal.

That sounds like, ahem, good old 2-wire RS485 It means they have a processor in the tuning head.

It also means the tuning head has some potential for radiating stuff.

Peter wrote:

That sounds like, ahem, good old 2-wire RS485

Quote from the Trig manual:

TMAP is a Trig proprietary bus based on RS485 signalling"

Peter wrote:

It means they have a processor in the tuning head

I’ll give you an even better argument: the tuning head has an LCD to show what it is doing so yes, it must have at least one processor. Lots of opportunities for radiation indeed, but strangely enough I experienced none though I gave it every chance with those long 0,50 mm2 copper wires.