Plumbing in tunes

Hawkeye7A · #1 01-26-2009, 10:14 AM

After about 75 hours of flying in my -7A I installed an auto docking station for my XM receiver for the tunes. It introduces into the audio a faint high-pitched tone that varies in intensity with the engine RPM. If I unplug the power cable from the back of the dock, it quits. If I place a diode in the positive line will/should that eliminate the tone? Another problem with it is that it continually shuts off and turns back on of its own mind. I suspect this may be due to vibration. Any ideas? Thanx.

bsacks05 · #2 01-26-2009, 10:36 AM

I have the same faint high pitched whine with my XM setup but it is only noticeable on the ground with the engine at idle so it doesn't bother me.
As for it shutting off, I have that problem with the unit in my car which is an older XM reciever. I took off the back plate and noticed that the power receptacle tabs were not making contact with the board so I had it resoldered. I used to transfer my XM reciever between my car and plane and the frequent plugging/unplugging must have caused the problem. I have since put a newer model receiver in the plane where it stays and has not been a problem since.

txaviator · #3 01-26-2009, 11:12 AM

I have a few XM units (in my car and in my wife's car). Mine is one of the older Delphi units which I can transfer between vehicles, to the portable boom box, etc.

It automatically shuts down every three hours....precisely at 180-minutes. I asked XM about it, and they told me that some of their units would indeed automatically shut-down. Perhaps your XM unit is an older one like mine and does the same thing?

YMMV,

Ironflight · #4 01-26-2009, 12:02 PM

Quote:

Originally Posted by Hawkeye7A

After about 75 hours of flying in my -7A I installed an auto docking station for my XM receiver for the tunes. It introduces into the audio a faint high-pitched tone that varies in intensity with the engine RPM. If I unplug the power cable from the back of the dock, it quits. If I place a diode in the positive line will/should that eliminate the tone? Another problem with it is that it continually shuts off and turns back on of its own mind. I suspect this may be due to vibration. Any ideas? Thanx.

Hi Hawk,

I can't address the power off problem, but the humm is something that many of us have experienced with external audio devices (MP3 players, XM radios, etc. AS long as the unit is operating on battery power, the only place it is grounded to the airframe is at the audio jack. When you plug the power cord in to the unit, there now exists a second ground path to the airframe. Depending on if the grounds are isolated inside the unit or not, you can get a ground loop, and therefore, a nice little hummm to go with your music. The 396/496 are notorious for this, but Garmin apparently fixed it on the 696 (or my ears have gotten so bad, I can't hear it.

There are little noise filter boxes you can get to go between the audio cord and the airframe jack to eliminate this. Some work, some don't - I got one handed to me by anther RV'ator and it works great! Since I have the 696 in my airplane most of the time, the little filter moved to Louise's airplane so she can listen to the XM on her daily commute. Search the archives for "noise filters" or something like that for more threads on the topic.

Paul

Hawkeye7A · #5 01-27-2009, 11:21 AM

Thanx for the ideas. I'll see what works.

Jamie · #6 01-28-2009, 08:43 AM

Hawk:

Which XM receiver are you using? Are you using the newer portable ones with the hard drives? If so, that could explain the pre-mature shutting down because many of the newer ones that double as an MP3 players have hard drives in them. Hard drives should be avoided like the plague in our airplanes, especially if they are hard mounted to a metal surface.

Danny7 · #7 01-28-2009, 09:57 AM

Quote:

Originally Posted by Jamie

Hawk:

Which XM receiver are you using? Are you using the newer portable ones with the hard drives? If so, that could explain the pre-mature shutting down because many of the newer ones that double as an MP3 players have hard drives in them. Hard drives should be avoided like the plague in our airplanes, especially if they are hard mounted to a metal surface.

hard drives like spinning disks, the things in computers? as compared to memory stick type memory?

Hawkeye7A · #8 01-28-2009, 11:57 PM

Quote:

Originally Posted by Jamie

Hawk:

Which XM receiver are you using? Are you using the newer portable ones with the hard drives? If so, that could explain the pre-mature shutting down because many of the newer ones that double as an MP3 players have hard drives in them. Hard drives should be avoided like the plague in our airplanes, especially if they are hard mounted to a metal surface.

I've owned this one for several years now and don't remember exactly when I got it. It's given me no problems in two different cars, the house, the boombox in the garage(formerly my airplane factory) and even the '59 C172 I used to own. I'm thinking it may just be the extra vibration on the RV (I've got it rigidly mounted on the panel) but don't know for sure. Haven't gotten an audio filter for it yet. Even with the XM receiver off I still get the side tone in the headsets until I unplug the power cable feeding the receiver base. Another post mentioned that some of them had timers to shut down after a couple/three hours but this one shuts down after about 10 seconds and then another 10 seconds or so it restarts, the tunes come on, and then shuts down again. While taxiing at low speeds it seems to be OK. It's after takeoff with higher power/RPM that it starts acting up. Very annoying. It's piped into the audio input on my intercom, a Flightcom 403 with all of the wiring shielded audio cable. I've got the power tapped into the same buss terminal that feeds all of my other avionics: Comm, Xponder, JPI-700, etc. so I don't think it's a loose or otherwise faulty power supply point. Hope this helps.
Again, thanx to all of you who are taking the time to help me address this issue. VAF rocks! (Wish my XM did!)

Jamie · #9 01-29-2009, 06:24 AM

Quote:

Originally Posted by Danny7

hard drives like spinning disks, the things in computers? as compared to memory stick type memory?

Yes, some of the XM receivers that also play MP3s have physical spinning hard drives. It's quite difficult to know which ones actually DO have a hard drive because they aren't in the technical specifications documents on the XM website. In fact, they don't even tell you how much memory they have, much less the type of memory.

Hard drives should not be used in high vibration environments, especially at altitude.

The heads of hard drives ride on a cushion of air...air that is obviously a lot thinner at altitude. Add vibration from a firm mount to your airframe and you are doing your hard drive no favors, that's for sure. My wife's classic iPod will only work in our airplane if she holds it. If we velcro it to the panel it will start cutting out. My little iPod nano (which is solid state) does not have that problem at all. Also, my airplane is pretty darn smooth (0.01 ips when when I dynamically balanced it...obviously we didn't add any weights).

XM is so cool in the airplane. It's really neat to fly from Oshkosh to Atlanta and listen to the same station the entire time, or catch up on news, or whatever. I'm a bit of a news nerd so I'm frequently on the news channels.

Currently with my setup I'm using XM on my 496, but I think I'm going to install an external XM radio and put it on the passenger side. This way my passenger will have more control of the entertainment.

pilot2512 · #10 01-30-2009, 01:39 AM

ok here's my 2 cents worth. Can you shut down your alternator with a switch? try that and see if it helps. I've had similar problems in Cessnas and Pipers. The alternator has to much ripple and that is what you are hearing. I used to install a filter at the alternator to fix it (or replace an existing one). Its just a big capacitor to gelp smooth things out. That may also cause your xm problems too. they are designed for cars that have very steady voltages.

Jay