Update on CHT & EGT jumping when I press the PTT

[rfazio1951]

I posted previously that When I pressed the PTT for my com radio the CHT & EGT temps jumped up a lot, like 300 degrees or so. This is in my RV-6. It was really not a problem except when you were leaning and trying to get to the best temp. If you hit the PTT you would mess up the lean process. I was also concerned that I might be somehow hurting the EMS-220 module. I had the Icom 210 radio sticking out through a bulkhead behind my panel and right behind it was the EMS-220 module. It was probably 2" away.

The first thing I did was to re-locate the module and wiring toward the co-pilot side of the aircraft about 12". No change noted. To be fair thought the antenna coax (RG-58) was routed near the EMS module and the wiring. Next I installed the L-Com filters on all three DB connectors on the EMS-200 module. No change noted. This weekend I connected up a new coax cable (RG-400) to a new antenna. I did not like the wingtip antenna I had in the right wingtip. I installed a new antenna out the bottom of the aircraft and routed new RG-400 coax to it. I routed the coax away from the EMS module. This not only gave me a much better antenna but when I press the PTT the CHT & EGT jump much less than they did before. They jump up between 25 and 50 degrees now. Way better than the 300 or so before. Next I'm going to try and get the antenna wire further away from the EMS module and the CHT & EGT wiring. I may also try shielding the CHT & EGT wiring from the antenna coax. Just figured I'd post what I found.

 

[jakej]

Richard

I'm working with Reidvaitor on this same issues - IMO you are both on the same track ie coax and grounding to fix these 'issues'.

RG400 (or similair low loss coax) is the ONLY type to use. Good antenna bonding is also ESSENTIAL.

HTH

Jake J

 

[DennisW]

I have the same issues with the engine displays and also see the Autopilot bugs jump all over when I transmit. I have an Arion Lightning and have not had a chance to work on the issue yet. I will let you know how things work out. I will be looking at grounding (a big issue in composite aircraft) and the coax that was installed. The EMS is under my seat about 3 ft from the radios. I have an SL-30 and SL-40, so two dipole antennas, one in the vertical stabilizer and one just behind the bulkhead behind the pilot's seat. The coax runs along the side of the fuselage and the SMS wiring runs through the middle of the console to the computer below my seat. Although the support folks say this is a rare issue, I have heard from other people that it is very common.

 

[preid]

My update is the same as Dennis. I continue to see the spikes but have determined to look outside versus the instruments when transmitting as I was unable to resolve the issue moving everything around.

 

[jakej]

I have the same issues with the engine displays and also see the Autopilot bugs jump all over when I transmit.  I have an Arion Lightning and have not had a chance to work on the issue yet.  I will let you know how things work out.  I will be looking at grounding (a big issue in composite aircraft) and the coax that was installed.  The EMS is under my seat about 3 ft from the radios.  I have an SL-30 and SL-40, so two dipole antennas, one in the vertical stabilizer and one just behind the bulkhead behind the pilot's seat.  The coax runs along the side of the fuselage and the SMS wiring runs through the middle of the console to the computer below my seat.  Although the support folks say this is a rare issue, I have heard from other people that it is very common. 

Dennis

I have done installs on several Arions here & we don't see (well nobodys told me they have 'issues' yet) the problems you have What type of coax do you have ?
BTW - some of the aircraft I work on don't allow me to separate the coax from the rest of the wiring bundle & we still don't have problems, hang in there I'm sure you'll get the issues resolved.

Jake J

 

[loanguy]

I am in same  situation with egt and cht jumping on PTT .

I am very close to first flight, so any help woild be great.

Jeff

 

[DennisW]

Jake,

I have RG58 C/U cable and will likely switch to RG400, but that is what I have currently. Other than switching to RG400, do you have any other ideas?

 

[JTD]

I have the same issue. RG400 cable and several feet seperating the EMS unit and coax

 

[jakej]

Troubleshooting without seeing the plane can be difficult & there are so many variables.

From my experience, if you are using RG400, separating the coax from rest of the loom doesn't make any real difference unless heavy power (battery) cables are involved.

Most of the issues are with composite aircraft however can be with aluminium too.
Coax connectors - use the crimp type & make sure the pin is fully pushed in, ie make sure the end of pin is almost flush with 'face' of the BNC.  It's easy to assume that we know how to crimp these but I find many are poorly done.

Although you may have a manufactured antenna I'd still do a SWR check to eliminate that as a causal factor.

I can't stress this strongly enough - get rid of your RG58, it WILL MOST LIKELY cause problems now or later.

HTH

Jake J

 

[marchudson]

I went through this process with my RV-7 during the install. Composite aircraft might be different. I was getting a 200-300 deg EGT/CHT jump during transmit from both GNS-430 and SL-40. If this is happening inside the shop or hanger, bring it out in the open and give it a try. Lots of reflected RF inside those metal buildings. I used RG-400 on everything. Checked the SWR on both belly mounted whip antennas and they were both reading fine. Still lots of noise coming from the EMS. I went as far as taking the SL-40 out of the aircraft and wiring it up completely separate from the aircraft, antenna and all. Still lots of RF noise. Ordered three L-Com filters for the EMS connectors and the problem was solved. I now have zero RF noise coming from the EMS. L-Com sells a Ferrite and a Capacitive filter. If you try this route, make sure you get the capacitive filters.

 

[jakej]

Marc

Are you saying you added the 'filters' to the EMS 220 in addition to the ones on the SV's ?

If yes, then that's interesting as I've never had to go to that degree of protection - but hey, if it works then that's all that matters

Jake J

 

[preid]

I've determined that I would need to do what Marc did, I actually figured this was the only solution but was told it was not a supported solution by Dynon and Richard Fazio stated it did NOT work for him (Next I installed the L-Com filters on all three DB connectors on the EMS-200 module. No change noted). I did everything and nothing resolved the issue.
As mentioned previously, I have to live with this issue. Nothing left for me to do and until Dynon supports the filters that is not an option for me, specially at the price L-com wants for them.

 

[DennisW]

The noise is not coming from the EMS, it is getting into the EMS and the Autopilot as well. I have been told a ferrite filter at the antenna end of the coax may fix this. I just need to confirm the filter to purchase to see if it works. I still need to do some trouble shooting here. I talked to Robert Hamilton, Director of Sales and Marketing for Dynon at the LSA Expo on Saturday. A 50 ohm load at the radio should determine if there is a grounding problem or not. Putting the load on the antenna connection of the radio will take the coax and antenna system out of the loop. If the noise issue is still in the display after using the load, then it is a grounding issue. If not, then it is in the coax / antenna system. Putting the load on the end of the coax can take the antenna out of the system, so this will tell you where the problem is, but not how to fix it. Time to go dig my electrical stuff out of the moving boxes.

 

[marchudson]

reidvaitor - I'm not sure why the fix did not work for Richard Frazio.  I posted the details about what I did so that guys would know to buy the capacitive filters instead of the ferrite filters if they decide to go this route.  Also, not sure what price you are looking at but for $30 you can get all three filters from L-Com.  http://www.l-com.com/item.aspx?id=3138

(Dynon Tech Support here - Marc's link is for a "D15" filter, and the CHT/EGT connector is a "D25"; a filter for THAT is http://www.l-com.com/item.aspx?id=3139.)


jakej - I don't have the filters on the SV panel, only on the EMS. 

Being a EE, I was just going to wire up several filter capacitors in parallel with the inputs to the EMS module in order to solve this problem.  That was before I found the L-com filters.  Elegant, cheap, easy solution. I'm not sure but I believe Dynon used some of these filters on the SV panels themselves with a few customers that were having a different RF problem. 

Dennis - I agree the noise is not coming from the EMS.  My problem, and I'm guessing a few others is that the EMS was unable to reject the 30-300MHZ RF band from the VHF radios on the input side.  These 820pf capacitors do an excellent job of shunting the RF to ground.  It appears that only a handful of installations were experiencing this problem, myself being one.  If it is getting into the autopilot system, I'm guessing you have an antenna or coax issue.  Can't tell without actually putting some test equipment on it though.  Have you checked the antenna with an SWR meter?  My RF problem was very easy to isolate once I built a remote VHF transmitter. 

YMMV

 

[DennisW]

Dennis - I agree the noise is not coming from the EMS.  My problem, and I'm guessing a few others is that the EMS was unable to reject the 30-300MHZ RF band from the VHF radios on the input side.  These 820pf capacitors do an excellent job of shunting the RF to ground.  It appears that only a handful of installations were experiencing this problem, myself being one.  If it is getting into the autopilot system, I'm guessing you have an antenna or coax issue.  Can't tell without actually putting some test equipment on it though.  Have you checked the antenna with an SWR meter?  My RF problem was very easy to isolate once I built a remote VHF transmitter. 

YMMV

I have not checked the antenna with a SWR meter. Don't have one, but I suppose I could borrow one somewhere. In any case, I have not had a chance to do a lot of trouble shooting. I appreciate the input and work you guys have done. I am an EE as well, but haven't done any real EE work in years. I do, however, know how to trouble shoot systems and understand the information you are sending.

 

[DennisW]

I installed the L-Comm Capacitive Filters on my EMS and it did not fix the issue. Still looking for answers. I'll let you know what I find.

 

[preid]

Darn!
Thank you for your results I mentioned previously that Richard tried the capacitors and that did not work for him (either) you confirmed this is not the solution.
Jake was great trying everything with me, I have RG400 and moved everything around, still an issue. I determined to let someone else figure out for us.I stopped looking at the CHT's; after a while one gets accustomed to it so it's not a big deal.

 

[jakej]

FWIW guys, I've never used the 'filters' on the EMS 220 just have them on the SV's.

Jake J

 

[DennisW]

I'm going to go to the airport with a roll of aluminum foil and find out where the noise is getting in. With the Dynon wiring harness, there are open cables everywhere for additional ADAHRS, EMS, GPS units, so in my opinion, they are just antennas waiting for a signal. After I cover up a few cables, maybe I can figure out what I really need to do.

 

[DennisW]

FWIW guys, I've never used the 'filters' on the EMS 220 just have them on the SV's.

Jake J

Jake,

If you have the newer versions of the displays, they already have filters, so adding additional filters could actually hurt the system rather than help.