Astro Spectra W3 Microphone Hum

[NSPD]

My buddy has a VHF 110W Astro Spectra W3 mounted in his vehicle that has developed a low hum in the transmit audio, which seems to be around 300 or 400hz. It is present on both analog and digital transmissions.

At the time of installation a couple of months ago, the transmit audio was perfect. All of a sudden one day, the hum started. I questioned him as to whether or not he had done anything abnormal to the radio, and he stated that he had dropped the control head that day.

Though a search on here, I got information that the red and black microphone wires being too close to a large IC on the circuit board was potentially the problem, so I opened up the control head and taped the wires out of the way away from the IC. This worked for about two weeks but now the hum is back, along with what sounds like wind noise in the background. It is there in analog, and it seems to be degrading the audio quality of the digital audio quite a bit.

I keep seeing references to the "characteristic W3 hum", but I cannot seem to locate a thread detailing how to fix it. Anyone have any ideas or know what might be causing it?

[K8TEK]

There is a wire in the control head near the microphone element that is introducing crosstalk in your transmissions.

[NSPD]

Can you elaborate a little bit more on what I need to do to fix the problem permanently?

Thanks!

[K8TEK]

The best way to stop crosstalk is to use a shielded cable, like RG-174 or something similar. Almost all HHCH Spectras exhibit this problem.

Replace the wires going from the element to the board with shielded cable. That will solve the problem.

[SD70MAC]

Anyone got any pictues of this modifcation ? I need more info on this please..

[SD70MAC]

I been racking my brain to fix my W3's transmit hum and I finally found a way to fix it and here it is. I raised the mic element above the board with a piece of plastic tubing and this stopped the crosstalk hum completely. The tubing is 3/8 diameter X 7/16 H with a notch. It is attached to the board with Black Silicone ,a very small amount applied with a toothpick. I put some dense foam(not pictured) in the tube and around it to deaden any noise of your hand moving on the mic. I tried using a smaller diameter tubing ,but it cut the audio into the mic. I also twisted the mic element tightly and bent the wiring toward the bottom on HHCH.


I hope the link to pictures work this is the first time I have used this type link.








http://s1240.photobucket.com/albums/gg5 ... adradionc/

[SD70MAC]

Also another way to view the photos.


http://forums.radioreference.com/motoro ... ost1798620

[SD70MAC]

I been racking my brain to fix my W3's transmit hum and I finally found a way to fix it and here it is. I raised the mic element above the board with a piece of plastic tubing and this stopped the crosstalk hum completely. The tubing is 3/8 diameter X 7/16 H with a notch. It is attached to the board with Black Silicone ,a very small amount applied with a toothpick. I put some dense foam(not pictured) in the tube and around it to deaden any noise of your hand moving on the mic. I tried using a smaller diameter tubing ,but it cut the audio into the mic. I also twisted the mic element tightly and bent the wiring toward the bottom on HHCH.


I hope the link to pictures work this is the first time I have used this type link.




http://s1240.photobucket.com/albums/gg5 ... adradionc/

I have also added an Electromagnetic Shield in the W3 HHCH. I could shorten the tubing when I installed this ,but I just left it the way I had it.

[SD70MAC]

Here is the Mouser Part # for sheet of the shield material. It is 0.1mm thick and about 8" x 11" before you cut it to fit.





Mouser P/N 517-AB5010S



http://forums.radioreference.com/motoro ... ost1813307

[SD70MAC]

I was fixing another W3 and it did not have as hot of a mic as the one I have so I had to make a revision to my mod.


Cut out the mic holder that it fits in from the factory.

http://s1240.beta.photobucket.com/user/ ... 3183912962


This one had a worse hum so I had to go with a copper tube instead of plastic.( It is still 3/8 X 1/2) Wrap the copper tubbing in the EM shield before you instal the tube. Put a piece wire insulation around the mic element so it does not make contact with the copper. Twist the mic element wire as tight as possible then instal it in the tubing. Place a small piece of the EM shield over the mic element plug also.

http://s1240.beta.photobucket.com/user/ ... 6371675684

I think I will go back and mod mine just like this later.

[SD70MAC]

another way to view pictures

http://forums.radioreference.com/motoro ... ost1847308