NAV Ident Drop-out During TX
Printed From: Avidyne
Category: Avidyne General
Forum Name: IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM
Forum Description: Topics on Avidyne's IFD 5 Series and IFD 4 Series Touch Screen GPS/NAV/COM
URL: http://forums.avidyne.com/forum_posts.asp?TID=1177
Printed Date: 05 May 2024 at 9:53am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: NAV Ident Drop-out During TX
Posted By: DavidBunin
Subject: NAV Ident Drop-out During TX
Date Posted: 18 Nov 2016 at 8:45am
|
I know there has been a long-standing issue with the sensitivity of the VHF Nav receiver and the ability of the unit to decode the station identifier. I also read that there is an improvement to this functionality in the next software release. What follows might be the same issue, or it might be something different. I was out flying practice approaches the other day. While flying the ILS at a towered airport, I noticed that the ILS identifier would flag each time I transmitted on the Comm radio to talk to Tower. This naturally produces a CAS message for the pilot to check the navaid manually. Of course, the identifier doesn't get decoded again until the radio "hears" the Morse code sequence correctly and completely at least twice in a row. Which is right about the time I need to broadcast my new position again to Tower. (Entering/exiting the procedure turn, crossing approach fixes.) I understand that a VHF Com broadcast in close proximity (from the same radio, or even from the same airplane) can overload the VHF Nav receiver. If I had been transmitting on my "other" radio, I wouldn't even be making this post. But within the IFD itself, I see a potential solution. Seems like there could be logic within the IFD to "hold" the VHF Nav station identifier data while the VHF Com is transmitting. Then, when the broadcast ends, the IFD only needs to 'listen' to the Morse code once to see if it still matches the held value. If the VHF Com signal is being broadcast from a non-IFD radio onboard the aircraft, then I would expect the current behavior. I see the CDI flag on the other Nav receiver when a radio is transmitting, but the flag pulls away the moment transmission ends, and that radio doesn't have CAS messages. David Bunin |
Replies:
Posted By: AviSimpson
Date Posted: 18 Nov 2016 at 10:09am
|
Interesting. I was just flying an ILS this morning and didn't notice any anomalies, I'm not saying they don't exist, just didn't notice it. Can you send your logs into Tech Support and see if there is something else going on? ------------- Simpson Bennett Avidyne Corporation Product Manager |
Posted By: DavidBunin
Date Posted: 18 Nov 2016 at 5:19pm
|
Sure. I can download the logs the next time I'm at the hangar. The approach was the ILS 18 at KHQZ. ILS frequency is 109.75 and the Tower frequency is 120.30. I was flying the full procedure turn and they wanted my position entering the turn, existing the turn, passing PQF, and so on (it was a busy day and they're a non-radar tower). I lost count of how many times I had to clear the CAS message during the approach. |
Posted By: MysticCobra
Date Posted: 19 Nov 2016 at 8:41am
| There are many reasons why the COM portion of a radio might interfere with the NAV portion, and if the radio is properly designed and working normally, the problem won't be inside the radio itself. Antenna lead routing and antenna radiation and reception characteristics are your more likely culprits, but unfortunately not easy to troubleshoot/diagnose. You may find that the problem only occurs with certain combinations of transmit/receive freqs, also. |
Posted By: DavidBunin
Date Posted: 21 Nov 2016 at 11:33am
|
Luckily (in terms of troubleshooting) or unfortunately (in operational terms) it seems pretty consistent on the ILS closest to my home airport. I sent the logs to Tech Support, except for the GPS log and the Flight log, which were too large for email.
|
Posted By: DavidBunin
Date Posted: 03 Dec 2016 at 6:55am
All quiet on the Western Front. Too quiet. Did my emails even go through? David Bunin |
DavidBunin wrote:Posted By: AviSimpson
Date Posted: 06 Dec 2016 at 10:42am
|
Yes, I think you received a response from the Tech Support team yesterday. ------------- Simpson Bennett Avidyne Corporation Product Manager |
Posted By: DavidBunin
Date Posted: 07 Dec 2016 at 3:00pm
|
I don't see anything in my inboxes or spam folders. Which email address did they use? David |
Posted By: AviSimpson
Date Posted: 07 Dec 2016 at 4:27pm
|
My mistake, they said they had replied but it must have been someone else. In any case, you should be hearing from someone soon. It sounds like the com and nav coaxes are too close or they might need to be replaced. ------------- Simpson Bennett Avidyne Corporation Product Manager |
Posted By: DavidBunin
Date Posted: 08 Dec 2016 at 10:19am
| Ouch. Replacing those cables would be a real pain in the rear-mounted antenna. I might have to live with it for a while. Thanks for taking a look for me. |
Posted By: MarkZ
Date Posted: 08 Dec 2016 at 12:58pm
| Maybe reseat the box? Fixed one of my issues on a different radio (lazy bearing pointer). |