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GRT Mini-B radio interference

Mark Albery

Mark Albery

Well Known Member
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?
 
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
 
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!
 
Mark Albery said:
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!
Click to expand...

It looks like Digikey has it http://www.digikey.com/product-detail/en/FCE17A15AD290/FCE17A15AD290-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
 
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: [email protected]

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
 
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.
 
Initial results of field approach given to me by Marc

Reckoner said:
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: [email protected]

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
Click to expand...

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.
 
Excess Wire

Mark Albery said:
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.
Click to expand...

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
 
Dual Mini's

This thread was interesting to me because I have dual Mini's in my panel and was getting really bad squelch breaks on both of my radios, a GTN650 and a GTR200.

I moved my ground wire on the MiniX without a magnetometer from Pin 7 to Pin 12. On my MiniX with the compass module, I connected the GND wire from Pin7 to the magnetometer GND wire going to Pin 12.

So far so good. Absolutely no broken squelch on the lower freq's. Mine was really bad on 120-123.** freq's. Both radio's were clear of it this morning.

Will report back if anything changes.
 
Follow up

OK, it's been a while and I have made a bunch of flights and am happy to report that I have not had any more problems with breaking squelch on either of my com radio's since I moved the ground wires as discussed in the above thread on both of my GRT mini's.

I don't understand radio waves and electrons like I should, but this seems to have worked.

If you are getting unexplained squelch problems on your com radios and have a Mini installed you probably want to try this.
 
GRT Mini-X radio interference

I've had the same GRT Mini radio interference problems from day one, and gotten some of the same advice from GRT. I changed the power connection as suggested, and beyond that ran a 1/2" wide braid from the case to my ground buss behind the panel. The latter made the greatest difference, and most of the time there are no squelch breaks, but occasionally there still are some. I happen to be an electrical engineer, retired from Bell Labs, and with a great deal of RFI mitigation experience, so I have several time offered GRT to try to fix this, no charge, but much to my frustration, they have completely blown me off.

So, recently I tried to take another run at this, and took my spectrum analyzer out to the plane, with results in the included pictures. There are two spikes- 132.075MHz, the DuPage Airport ATIS, and 120.90 Mhz, the tower. In the first picture is the background, with the GRT turned off, but multiple Garmin pieces, all with switching power supplies also, on. The others are with the GRT Mini on. It puts out a whopping spectrum of noise spikes at about a 1MHz spacing, so no wonder. Now, if they could just cough up a schematic for their switching power supply/battery charger, maybe we could do something about this? GRT, do you read these posts?
GRT%201a.jpg
GRT%202a.jpg
GRT%203a.jpg
 
Had mini b in panel before the Garmin G5 came out. Fought the same exact noise issues you're dealing with. We have since switched to The G5 and that cleared up the noise problem!😀
I have a customer who still has the mini and is fighting the noise issue also.
I am suggesting he dump the mini and put in the G5.
Good luck!😂
 
Yup, exact same scenario in my case, only I would gladly put in a G5, except it does not allow mounting on a canted panel, which mine is. The Mini does have an angle correction in the setup for an angled panel. That's another windmill I have been tilting against - trying to get the Garmin folks to add the ability to null out a canted panel on the G5, but they have bigger fish to fry!

Cheers!
Reinhard Metz
 
We put a G5 in a Lancair IVP with a slightly canted panel. Garmin said it wouldn't work. We prepared a an adapter but decided to try it without it.
It's been functioning fine without it.
Give it a try!
 
That's enticing - wondered myself if the G5 wouldn't work anyway. My panel cant angle is about 12 degrees. A bit of glass work to fit the smaller footprint, but I really like the Garmin graphic presentation much better.

Reinhard
 
Hello Reinhard,

I haven't been on this site in a while so I though that I would check out what was happening in the RV world. I am glad I did.

Your original email sent on March 4th got sent to the wrong location. Your follow up email on March 17th did get through. I was going to reply. Greg Toman, the owner of the company, wanted to send you a response personally and did so immediately after, sent on March 17th. I definitely want to talk with you and was wondering why you had not replied. I suppose that you didn't get his email. He CC'ed me on the email he sent, so I sent you a copy of it to your AOL email. Let me know if you don't get it

Your images on your spectrum analyzer is consistent with an unmodified Rev A board. We are now shipping the Rev B board and modifying any Rev A boards.

For anyone that is having or had issues with noise with their Mini or know someone that does, email me directly with the issue and what was tried to fix it and any questions, comments, complaints or criticisms. I just really want to fix the issue and am going to handle it directly. If there is any issues with how our techs are handling the issue, I want to know that as well so I can fix that as well. It has gone on way too long.

-Marc Robertson
Project Manager
GRT Avionics
Email: [email protected]
 
Sent an email to "Reckoner" this morning, received a call back within a few minutes. Had a good chat with Marc. Without doubt this is one of the best aspects of dealing with GRT. One can talk to the engineer and get the real information with no marketing spin. Just the facts. I really appreciate this down-to-earth way of doing business.

In our conversation it became clear there is a fix for the Rev A boards (ours is one of the very earliest Mini's produced) that significantly improves the noise emission signature. Marc continues to pursue improvements - an encouraging piece of news. In the meantime I need to decide whether to send my Mini back for the Rev A board mod...

Again, kudos to Marc Robertson and GRT for being open to a forthright discussion.
 
Last edited:
GRT Mini radio interfernece progress

To provide an update on the situation: In fact GRT - Marc and Greg - did respond quickly and very positively to my offer to help identify noise sources and discuss fixes to the radio interference issue, but it turns out several emails somehow got misdirected or lost.

So, to be clear - GRT has been exceptionally forthcoming with information, I have taken my Mini apart and fixed it, and we have discussed several improvements. In fact, as Marc mentioned, they have a fix for rev A units and incorporated changes in later units. GRT clearly has this in hand now, and I have to say having having taken my Mini apart, it is a very nicely designed unit of highest quality. Sorry for some of the disparaging comments I made - I had just gotten a bit frustrated with the issue before.

Reinhard Metz
N49EX
 
Whats the latest?

I recently got warned off the Mini for this noise issue. Since were well on the backside of the 2017 calendar now, has this all been solved and "newly ordered" Minis are good to go as shipped?
 
I think the answer, based on my very limited experience with a sample size of one, is "yes". The Rev B boards, shipping in new units, has proven quiet in our aircraft.

Make sure you wire in accordance with the current installation manual.

Oh, I should mention that, while I have both the HX and Mini-X sitting side by side in the panel, my eyeballs clearly prefer the crispness of the Mini-X display. Love its internal battery which provides seamless backup in the event of an electrical system failure. If I were buying another Mini the internal battery would be a "must have" option.
 
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