MGL Avionics User Forum

I have an iefis G3 panel with an iBOX and I am trying to connect the Trig ty91 radio to it. I am using the RS232 port on the ibox and T3 and R3. I have the resistors in place in the leads, but the radio doesnt seem to working. For some reason altering the settings in the set up box doesnt change anything. For example, changing the RX squelch to zero doesnt bring in the background noise as it should do. Any ideas anyone?

I should add that I am not using the trig control heads and I am trying to control the radio directly from the iEFIS panel which I understand is possible.

I have checked the serial port diagnostics and when the connector is disconnnected there is no readout at port 3 on the RS232. When the connector is connected, but not connected at the radio end, there is a load of numbers and letters and question marks that appear in a flashing sort of sequence. This doesnt markedly change when the lead is connected at the radio end and then when the radio is turned on.

I seem to be able to control the frequency and can hear myself in the headphones and transmit and receive but only over a distance of about 30 yards. Even though the aircraft is still in the workshop being built I would have expected the range to be better than that, and my hand held picks up passing traffic from within the work shop. Why cant the project I am building.

I have a belly mounted comant antenna, and I am about to change the antenna cable to RG400 instead of RG58, but even that should explain why I get no background noise at zero squelch.

A few of the other settings in the set up box for the radio dont seem to make any changes either.

Any ideas?

From your description I would guess you have a short circuit in your antenna cable - most likely the connector that plugs into your radio.

I would be careful pressing the PTT under these conditions - radios do not like that and you are in danger of blowing the transmitter.

Regarding changing the frequencies but nothing else works - can you confirm that you are really changing the frequency on the radio itself (i.e. using a hand held to receive your transmission). Note that if your hand held is relatively close it will receive even if your radio is turned to a different frequency. Except your range will be very short so that can be the case here as well.

Can you change the radios volume from the EFIS ?

If not then I do not think your connection is correct or perhaps you have not set the EFIS serial port setup to use the Trig radio on that port ?

Also, if you have an older iBOX please update the firmware on it so it can do the Trig protocol. You can check the currently installed firmware of the iBOX if you go to diagnostics and look at your iBOX data.

Thanks for the reply.
I will check the antenna cable connections. I am also going to upgrade the cable to a Rg400 rather than the rg58 cable it has now. And use less adaptors.

I did think about the channel thing you mentioned. So this morning I set the hand held to a different frequency all together and tried it and couldnt hear anything on the trig radio - So I guess when it says a specified frequency on the EFIS it really is that.

Can you change the radios volume from the EFIS ? - I will try tonight and report back.

Regarding the serial port selection I have serial port 3 on the RS232 and have it selected to Trig Com 1.

I have also updated the firmware in the ibox and the efis panel recently so they should be up to date. But I will check of course.

I wonder whether I should try changing round the r3 and t3 connections on the rs232 connector to the ibox. At the moment I have pin 3 on the trig connector which is TMAP A going to ground via a 470 ohm resistor. I have pin 4 which is TMAP B connected to the T3 and R3 pins (7 and 8 respectively) on the RS232 connector on the ibox, however the TX line is interrupted by a 470 ohm resistor before it meets the RX line. The signal ground connection (pin 9) is spliced into the ground connection of the radio so that there is not a ground loop.

Can you tell me what the normal readout should look like under serial port diagnostics when when something is connected and working properly.?

I take it you have COM1 enabled under equipment setup and that you get a red cross over your radio interface status and popup if the radio is not connected ?
Does the red cross go away with the radio connected ? If yes it is receiving from the Trig.

The diagnostics does not show anything really meaningful other than that "data is happening". It means in your case that data is being received by the port. Configure your iBOX port 3 to not have anything connected - then look at the diagnostics. You should see a ASCII text message with a number that counts upwards. This text is sent by the TX line and should be received via the RX line via your resistor. That would confirm that all is well with Port 3.

Make sure your resistors really are 470 ohms.

The TMAP is a RS485 bus. What we do is make up 1/2 the bus by combining TX and RX on the RS232 but the TX goes via a 470 ohm resistor. This we do since we cannot switch the TX line off in RS232. The other half of the TMAP bus is hooked to a fixed level via a second resistor (this helps bias the TMAP receiver so it is in "no data" state when the iBOX is not transmitting. The TMAP however can transmit as it is easily able to drive the 470 ohm load connecting to the TX of the iBOX. The RX line sees that signal so all is well.
This kind of RS232 to RS485 conversion works quite well but is not suitable for long connections - RS485 uses two wires in a twisted pair fashion similar to the CAN bus and this can go long distances (your old analog phones uses twisted pair). The RS232 conversion we tested up to about 30 feet (much longer than what is typically used) and it works well.

Thanks for the help. I tentatively think I may have sorted it. I was thinking about the squelch issue and realised that when you have a good ‘signal’ on a radio, ie using a handheld outside, then the squelch kicks in at say 13-15 on my icom. However in doors it doesn’t kick in until a lot lower. So I figured that perhaps there was just loads of loss through the rg58 cable I had and their connectors. So I hooked in the antenna for my icom hand held directly into the trig radio and immediately I got a squelch sound. Not only that but increasing the squelch from 0-250 I managed to tune out the squelch noise. So at that I built a new antenna cable of RG400 cable. I hooked it up and then for some reason the radio wouldn’t come on. Red Cross etc. I fiddled with all the wiring and found one a bit loose, but nothing significant. I also got worried because without the trig connected to anything there seemed to be continuity at the antenna jack between the contact pin in the middle and the outside (ground). I figured this wasn’t right for an aerial, but it could be possible for the unit to disconnect the continuity once power is provided to it. After connecting it again it sprang into life and I could hear some big jets flying into a local airport. Bearing in mind my project is still in the shed I think that’s great. My only concern at the moment is that communication between the icom and the handheld seems to produce a fast drumming background. However listening to the passing traffic doesn’t.

Should I disconnect the signal ground wire from the rs232 port on the ibox.

The radio and the connector are grounded to a single wire going to a main aircraft ground bus. INternally of the connector for the trig there is a partial ground bus also between 9 and 19, which is what they require in the manual.

Thank you for your help.