xcom radio won't tx

[BRL]

Im wondering if anyone has experienced this problem : I am hiring the local school savanaha s which has a xcomm radio approx 2 mths old and when I plug in my bose a20 headset l can hear everything thats going on but when l try to transmit the tx sign comes up but no audio is going out, the other pilots say they can hear the carrier but no audio. The cfi did a master reset before any flights on saturday and the radio worked fine until l came along and when l changed headsets the radio wouldn't tx and wouldnt on the others that had been fine earlier, l then gave another pilot the bose to check in his Aircraft and they functioned perfectly so it would seem as if they are not comparable to the xcom any clues?

 

 

[Kyle Communications]

The mic polarity is wrong or you mic element is dead on the headset

 

 

[BRL]

The mic polarity is wrong or you mic element is dead on the headset

the headset works in a different aircraft so does this make it the h/set or the radio?

 

 

[Virago]

There are sometimes slight differences between mic plug dimensions. It could well be that the mic socket in the aircraft needs it's contacts adjusting. It could be just making contact with the aircraft's own headset but just missing out with your Bose headset plugged in. A long shot but certainly worth looking into. John.

 

 

[SilverWing]

It's the radio - call XCom. We've had the same problem on several recently delivered Foxbats. Soomthing about the firmware and the modulation setting.

 

 

[RetiredRacer]

We have a XCom radio in our RV9a. Wanting to have the bluetooth ability for the phone, I bought a Zulu Lightspeed but had problems with them working with the radio. As we were heading off on a trip to Vic from Qld I bought a Bose headset and they worked perfectly with the radio. I got onto XCom Australia and they did an adjustment to the headsets firmware (from my understanding). Now both headset's work perfectly.

 

 

[Kyle Communications]

I have 2 of Zulu 2 in my aircraft and on a Xcom they both work perfect the only thing I did have to do was lower the microphone sensitivity in the radio as the Zulu were outputting too much audio. The bluetooth has nothing to do with the airband radio it connects to a ipod or phone via bluetooth for phone calls or music

 

 

[Derribong]

I have been using a Lightspeed Zulu2 headset with an Xcom 760 VHF radio fitted to Savannah XL since 2013 without any problems at all, till about a week ago. The side tone on transmitting suddenly stopped and I found that the radio was not transmitting. I have since done a factory reset (by pressing two buttons simultaneously till 'reset' is displayed). Sidetone on pressing PPT button now restored and checked with other receivers that radio was transmitting. Thought the problem was sorted!
However these tests were done with the motor not running. Have since found that my transmissions are received loud and clear from pilot headset or passenger head set when the engine is not running but with engine running only the carrier appears to be transmitted. Other radios just hear a click. Radio displays TX when either PTT button is pressed.
Receiving is clear, no problem at all, just no transmitting with engine running.

There have no other changes to equipment in the Savannah.

Anyone have any suggestion? Any thoughts much appreciated.
 

[Kyle Communications]

The engine running shouldnt make any difference unless your regulator on the engine is putting out high volts or spikes..check your regulator output

 

[Derribong]

Thanks for that suggestion. Will look at that next. I wonder why the receiver sound quality is not affected in some way also?

 

[Kyle Communications]

radio micro processors can have a heart attack with unclean powersupplys

 

[Derribong]

OK, will check that the supply is clean, thanks.

[RFguy]

I agree with Mark.

what you can do , disconnect the generator/alternator (fuse/CB) ( so you are on battery only)  and then see if radio has same problem with engine running.

 

could also be some vibration mode upsetting it, but unlikely. 

 

With a other radio you are testing with (portable, another plane) ensure at least 100m away.

 

glen

 

 

 

[Derribong]

Thanks Glen, planning to go today to do more tests.

[Derribong]

Problem solved. It's the Xcom radio, it does not like 13.9 volts supplied with engine running. Have added a Pololu 12V, 2.4A step down "buck" regularor D36V28F12 and the Xcom now reads 12.1 volts with motor running. Transmitts and receives fine.

Clearly something has changed with the Xcom as the Ducati regulator output has not changed. 

Perhaps the radio will continue to work with this reduced voltage, will wait and see.

 

 

[RFguy]

that  stepdown reg will probably generate a ton of switching noise.

 

and the BUCK regulator might shutdown when you battery volts goes < 12V. you need a BUCK BOOST regulator to handle that....

 

suggest a single series diode to drop 0.7V.  or single schotttky diode 0.4V drop, whatever is enough. that will take the very bottom of the radio voltage off, but the XCOM says its good for 15V, so you have some other problem.... 

 

either way, I think you have masked some other more serious problem, like high voltage spikes appearing on the V bus, or a sick radio.

 

either way, 13.9 V is TOO HIGH for a lead acid - you will gas your battery...

 

anyone else reading this, do not do this !

Edited May 11, 2021 by RFguy

[Derribong]

They are good points. Haven't found any problem yet but have only checked that the transmitter now works.

At least I now know that it is not RF interference or voltage spikes on the supply line.

Will try series of diodes next.

The only way to reduce the Ducati regulator output voltage is to replace the regulator I assume.

[RFguy]

Hi Derringbong

"At least I now know that it is not RF interference or voltage spikes on the supply line.". 
Well, no you haven't....  not really. at least you have a functional radio, but there is some other problem being masked. 

Mark (KYLE) , what do you think is the next move  ? what is this thing, Rotax 912 I gather ?

 

There is sooo little experience and understanding of this sort of problem in the avionics and aviation community. 

[RFguy]

Jaycar have some schottky diodes, put one of these in series. make sure the leads are restrained so that they cannot fatigue at the package (blob it in silicone) . it wont need a heatsink on that load.  that will drop the voltage 

 

Diode MBR735 Schottky 35V 7A TO-220-2 | Jaycar Electronics

 

https://www.jaycar.com.au/diode-mbr735-schottky-35v-7a-to-220-2/p/ZR1029

 

but you should  not need to do this, this is a Vbus high voltage spikes OR a Radio fault.

 

On the radio side of that dropper diode, put one of these across the + and -. make sure its all fused

 

https://www.jaycar.com.au/p4ke-13-6v-16a-standoff-400w-ac/p/ZR1162

 

P4KE 13.6V 16A Standoff 400W AC | Jaycar Electronics

 

banded end goes to positive ,other to negative. 

this will shop the spikes off, to some degree,  the rating is not really right , but it will do the job for a good test.

[Derribong]

Thanks RFguy will give that a try.

 

[RFguy]

PM or call me if you need to 

 

[onetrack]

A poor connection somewhere, with high resistance, creating a voltage spike to the radio?

[Kyle Communications]

The radio has a issue..it should work correctly above 13.6v. The rotax generator is horrible for spikes and the rotax regulator is nothing spectacular..they get really hot internally and get bad joints on the bridge they use inside this brings all sorts of issues like noise and spikes as well. The best way to see if its your radio is pull it out and set it up on a powersupply on the workbench with a clean DC source then raise the volts and see. This will tell you a lot then. Most regs are putting out 14.2 or so volts when the engine is running . The other thing to check too is the 22uF cap that should be on the output of your regulator. if its old it could be snookered too and that helps stop spikes  and even though Rotax say that is a option it really needs to be there all the time but like all caps especially ones that are getting hammered wont last too long.

 

[Derribong]

Update: Checked again today in air. Radio works just fine RX and TX on three tested frequencies. Xcom radio has mode to display supply voltage, in air it reads 12.09 volts. Regulator is supplying at 14.2 volts. Checked information with my battery EXT20L recommends charding at between 13.8 and 14.6 volts so that seems OK.

Clearly the radio has a "fault" in that it used to work fine at the regulated voltage for the last 6 years.

On engine off after landing RX still fine and Xcom reads supply voltage at 11.15 volts. 

I feel that is problem solved, for the time being at least.

Cheaper than buying a new radio. Hope I'm not speaking too soon!

Thanks to all for helpful suggestions.