Radio hash Noise when Turn on HDX

[Bardample]

I need some help to point me in right direction. I have a 10 year old RV 7 with Icom 210 radio, an FData AP 60 audio mixer ,a PS Engineering 1000 II intercom along with a Dynon HDX. Apart from past squelch issues with the Icom, the system has worked well and the headphone sound has been excellent. Just recently after switching master and avionics on there has been lots of hash backround noise ( even before engine start). I can still transmit and receive but the hash noise is extremely distracting.

After turning all switches on and off ( including alternator whilst engine running), I concluded the noise in the headphones ( whilst radio is on) is only there after I switch the Dynon HDX on and the fan starts ( relatively new HDX install after recent upgrade from Classic Skyview. Its been fine for the last few months).

Can any one suggest whats the most likely cause. Thanks Jeff

 

[Rhino]

I'd check the wiring first. Do you use a common ground point? Did this start with the new HDX install, or sometime later?

Have you read this?

Ground Loops and Noise in Aircraft Systems

Quite a few forum threads and articles have at various times addressed ground loops, and their potential to cause noise or other interference in your avionics system. Simply put, a ground loop occurs when different paths to ground are used. The difference in resistance, or impedance, on those...

forum.flydynon.com

 

[Bardample]

Thankyou Rhino. This started recently ,some months after update. I shall read your posted attachment to reacquaint myself with grounding issues and go searching again looking for obvious loose connection. Regards Jeff

 

[wilkersk]

Have you recently brought any new gadgets into the airplane? Cigarette lighter style plug-in USB power supplies and rechargeable USB power-banks can generate RF noise. If they are located close enough to your radio, they can actually defeat the squelch circuit. You'll the the little "TX" icon iluminated on your iCom.

 

[Bardample]

No new usb power supplies. It only happens after HDX powers up to the active screen. Even with master switch on without engine running, If I switch off Radio, intercom, garmin gps, and only have hdx on I get the hash. So far I havent found a poor earth or shield, but I'm searching. I think is a loose earth or perhaps shield to or from the FlightData audio mixer. Thanks foryour advice. Jeff

 

[vlittle]

A solution to SkyView noise is to terminate the audio outputs of the EFIS with 10 ohm resistors to ground. This will attenuate both audio alerts and any noise, Then, increase the audio level in the SkyView settings.
Some of the of the noise that you are getting may be from the dimmer circuitry in the HDX, which changes with ambient light.

Here is my zero noise implementation:

FMI:

https://www.vx-aviation.com/sprocket/photos/panel_elec/schematics-2/EFIS.pdf

https://www.vx-aviation.com/sprocket/photos/panel_elec/schematics-2/AUDIO1.pdf

Note: the AMX-2A, AMX-4A, and AMX-10A audio mixers have adjustable per-channel levels to simplify installations.

 

[Rhino]

Help me out here, Vern. Since I don't have knowledge of the AXIS-25A, are you saying to take audio out at point A or point B in the diagram below?

And since audio L and R are typically joined coming out of the Skyview, Couldn't you just use a single resistor?

 

[vlittle]

Help me out here, Vern. Since I don't have knowledge of the AXIS-25A, are you saying to take audio out at point A or point B in the diagram below?
View attachment 6694

And since audio L and R are typically joined coming out of the Skyview, Couldn't you just use a single resistor?

You could use a single resistor to audio ground and tie Audio Out Left and Right together At point A. I show independent resistors for stereo intercom systems to support the possibility of future stereo warnings, like OnSpeed AOA systems use.

 

[Rhino]

I thought that might be the case, but I wanted to be sure. Thanks, Vern.

 

[Bardample]

Vern and Rhino,
thankyou for your help. Just now I have removed my Icom A210 radio and replaced it with a Trig 96 A Com radio after disatisfaction( for various reasons). I replaced and improved connections via the FlightData Audio mixer and wired mixer and radio to PS Eng 1000 intercom. I now have wired the Trig radio to input to-the Dynon HDX and can now have radio frequencies on upper R Dynon screen ( not possible before with the Icom and its software).
So far the radio is functioning without the hash that previously sent me to ask advice. The radio has no hash whilst flying and with the HDX turned on before startup . I hope that continues, so time will tell if my installation has solved my problem.

As a very much amateur avionics installer, I may yet need to use Vern's advice about resistor installation, if the hash recurs. I do not quite understand where the resistors go on the audio out wires. I have joined R and L audio outlets together ( mono to mixer) in, and the audio ground goes to the audio mixer gnd. If this hash reappears , where in the circuit do I place this resister as I believe the HDX mono audio signal still needs to input into the audio panel mixer.

Please pardon my naivety. I have looked at circuits drawn and can't work out where I would install the single resister if needed.

thankyou for your help . Jeff