# Morse code beeping on the radio, in the background of AM frequency band



## bmusgrove (Nov 2, 2008)

2010 CC Lux. OEM touchscreen AM, FM, Sirius and 6 disc changer. 
Head unit replaced under warranty. Ever since replacement , AM band has a background high pitched morse code beeping sound. I hear it across the spectrum but it is strongest from about 1000 to 1700 on the dial. I listen to a station at 1080 and it is so bad as to be unusable. I have another 2010 CC lux with premium sound that does not do this. Occasionally as you go under a bridge you may here it briefly. 
It is a morse code sound and reminds me very much of station identification signal or a airport navigational aid. Any ideas?


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## bmusgrove (Nov 2, 2008)

The sound is repetitive . The beeping goes so fast I can't write it down, but it keeps repeating


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## BassNotes (Mar 16, 2005)

Are you near an airport?


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## bmusgrove (Nov 2, 2008)

Yes. Two major ones, Love Field and DFW International. As well as a few regionalairparks. Also have a major Antenna farm near the house 
I noted today that it is worse at 1080 MHz KRLD, a local channel, and at 1070 MHz , no channel there but you do hear bleedover from 1080. It is seen on any channel with a broadcasting station from 720 to about 1300 megahertz but at a much lesser extent. On those it sounds more like a carrier wave and a very faint morse code. It does get worse under cover, such as a bridge or parking garage. Today it is overcast and cool and it was barely noticeable.


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## BassNotes (Mar 16, 2005)

As I recall, airport non-directional beacons use amplitude modulation in frequency bands within and close to the AM broadcast band. The Morse code you hear would be the IATA code of the sending airport.


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## bmusgrove (Nov 2, 2008)

I did see that in my research, but in everything I read that occurs very low in the AM band, around the low 500's or lower. Not sure what the secondary harmonics for those frequencies are... From the sound pattern it must be a directional beacon, but I would expect to see that on both of my 2010's as the head unit is the same. That's what has me scratching my head.


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## BassNotes (Mar 16, 2005)

AM receivers usually use an intermediate frequency (IF) of 455 kHz, meaning that the local oscillator is at a frequency 455 kHz higher (usually) than the desired signal. If there's enough NDR beacon signal to cause non-linearity in the front end of the receiver, the intermodulation products might be detected by the receiver as phantom signals.


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## bmusgrove (Nov 2, 2008)

BassNotes said:


> AM receivers usually use an intermediate frequency (IF) of 455 kHz, meaning that the local oscillator is at a frequency 455 kHz higher (usually) than the desired signal. If there's enough NDR beacon signal to cause non-linearity in the front end of the receiver, the intermodulation products might be detected by the receiver as phantom signals.


 I actually understood that.  
I have several NDR's along the major roads I take to work. Cedar hill tx antennae farm, Red Bird airport, dallas Love Field airport, DFW Airport...


Essentially , based on the face that none of the other vw radios I have (including a identical model) do this, it would be a safe assumption the tuning oscillator is having some discriminatory issues, not rejecting the phantom signals. Supporting evidence also includes that driving under high tension wires destroys the station signal. It occurs primarily on station 1080 Am . Isn't that in the harmonic of the NDR transmission frequency?

I have noted that the issue is worse On hotter days and also when there is Less overcast. Last week we had several cool days withe heavy overcast and the issue was almost gone. 


Sent from my iPad using Tapatalk HD


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## bmusgrove (Nov 2, 2008)

*Resolution*

I finally fixed this after numerous trips to the dealer and many arguments. They wanted to do everything from replacing the back windows (bad Antenna) to
Replacing all antennae modules. I realize they were lying there teeth off when they told me they had already tried swapping a radio and that did not solve the issue. It was easily proved they had not even pulled the radio out and checked all antanae connections . All of the were good. While doing things by sheer accident I notice the problem was significantly reduce if the car was off and they key was out. If I put the key in and put it in the on position the noise issue returns.

Confirmed this several times. Pulled the powers block assemble out of the back of the radio and the issue went away.


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