GRT Mini-B radio interference

[Mark Albery]

I've recently been getting a lot of unsquelched background noise on my Garmin GTR200, but only really noticeable on my home tower frequency of 120.2.

A bit of experimenting shows that it goes away if I turn off my newly installed GRT Mini-B EFIS.

Any suggestions as to how I can tackle this?

[N661DJ]

Mark,
Had the exact same problem with my MiniB and Garmin GRT200. The final fix, after numerous suggestions from GRT was to install a discrete ground wire from the aluminum case of the Mini direct to the avionics ground buss.
Hope this helps,
Dick

[YellowJacket RV9]

If the ground strap doesn't work, I bought one of these for my D10 and problem solved.

http://www.digikey.com/product-detai...E17B25AD290-ND

Chris

[Mark Albery]

Chris,

I like the idea of the filter. Unfortunately the 15 pin version of that doesn't seem to be stocked by anyone.

So I guess I'll pursue the grounding suggestion and report back.

Thanks for the ideas!

[RV7Grinner]

I'm having the same problem with a Mini X. Please do post your grounding result. Thanks.

[YellowJacket RV9]

Originally Posted by Mark Albery

Chris,

I like the idea of the filter. Unfortunately the 15 pin version of that doesn't seem to be stocked by anyone.

So I guess I'll pursue the grounding suggestion and report back.

Thanks for the ideas!

It looks like Digikey has it http://www.digikey.com/product-detai...290-ND/3464959

The Amphenol part # is FCE17A15AD290 That's the model with the same capacitance as mine.

Again, grounding is a simpler solution, but this may be worth a shot if needed. Good luck

Chris

[Reckoner]

Hello Mark and others,

We want to help you fix the problem. If you are having or have had and fixed radio interference issues, please contact our support by phone or email. We would like to know:

1) What model Mini you have (Mini-B, Mini-X, etc.)
2) If you have a remote magnetometer for your Mini.
3) Any fixes that have failed or worked.

We will help you through either:
Phone: (616) 245-7700 Monday-Friday, 10 AM-12 PM and 2 PM-4 PM EST
Email: Support@GRTAvionics.com

The Minis have EMI filtering built-in to prevent radio interference. Unfortunately, the ground line has caused radio interference in the few cases that we have handled so far.

I have reviewed the proposed D-Sub filter. The 5,600 pF capacitors to ground will interfere with the Mini's high speed serial line's operation.

Regards,
Marc Robertson
Engineer
GRT Avionics

[Mark Albery]

Here's the follow-up:

I lifted the front deck, powered up the EFIS and used a hand-held ICOM to check for RF noise. On 120.2MHz I had a lot of noise that wouldn't squelch until I moved about 4-5 paces away. It was present up to 120.3 but not evident at other frequencies.

As I didn't use the data lines and only used the Dsub for power, the filter was still an option. That quieted the noise to the extent that the ICOM only picked it up at a couple of feet from the EFIS. Earthing the case appeared to make no difference. I then cut off the surplus wire for the data I/O and got a further reduction in noise to the extent that the ICOM had to be a few inches away to break squelch (the surplus wires had been coiled and zip-tied). I left enough wire to enable splicing at a later date if the wires were needed in future.

At that point I closed up and went flying. Result - clear radio on 120.2 with no background noise

It would be tempting to see if it would still be quiet without the filter, but I'll save that for another day.

[jclark]

Originally Posted by Reckoner

Hello Mark and others,

We want to help you fix the problem. If you are having or have had and fixed radio interference issues, please contact our support by phone or email. We would like to know:

1) What model Mini you have (Mini-B, Mini-X, etc.)
2) If you have a remote magnetometer for your Mini.
3) Any fixes that have failed or worked.

We will help you through either:
Phone: (616) 245-7700 Monday-Friday, 10 AM-12 PM and 2 PM-4 PM EST
Email: Support@GRTAvionics.com

The Minis have EMI filtering built-in to prevent radio interference. Unfortunately, the ground line has caused radio interference in the few cases that we have handled so far.

I have reviewed the proposed D-Sub filter. The 5,600 pF capacitors to ground will interfere with the Mini's high speed serial line's operation.

Regards,
Marc Robertson
Engineer
GRT Avionics

I was to test an approach in the field a few days ago but just around to it recently.

Short version of fix: Use pin 12 for all grounds.

--------------

If you have a magnetometer (pin 12 = ground) and you used pin 7 for "normal ground", then "Y" both grounds into pin 12.

I made a "Y" using DSUB pins, put the "normal ground" and magnetometer ground into it and plugged other end into pin 12.

Seemed to work.

Cannot say definitively as I was having other issues with radio squelch breaking. This is with a GTN 650 (I think you need to get the COMM s/w updated to 2.20 if it is not already) and a GTR 200. And make sure squelch is turn up appropriately on both.

I also had a set of HID lights that would break squelch on 650 100% of the time. So, I changed out the power packs to a different brand.

After doing the above, I seemed to have no squelch breaking on the GTR200 (with lights on) and a very occasional blip on the 650 on specific frequencies in the 120Mhz or so range. This was throughout a 2-hour trip with many frequency changes.

Upon landing, I cranked the squelch all the way up on the 650 and will test fly later.

Assuming this works as they expect, then they know specifically what they will do on all subsequent MINIs.

[skylor]

Originally Posted by Mark Albery

Here's the follow-up:

I then cut off the surplus wire for the data I/O and got a further reduction in noise to the extent that the ICOM had to be a few inches away to break squelch (the surplus wires had been coiled and zip-tied). I left enough wire to enable splicing at a later date if the wires were needed in future.

Leaving unconnected wires attached to electronic devices is virtually guaranteed to cause radio noise. "Unterminated" wired essentially become antennas that broadcast electronic signals as RF noise that can be picked up by radios. I would invest in a D-SUB connector contact insertion and removal too, and remove the unused contacts and wires from the Mini-B connector.

Skylor