Radio Hiss - Electrolytic Capacitor

Rumor has it that this discussion exists on another site, but I don't go there anymore.

I have an Xcom radio and it is recommended that a 22,000uF, 25V Electrolytic Capacitor be installed to help eliminate noise and I have plenty of noise. I installed a 10,000uf, 25V and that did help, but not enough. A local pilot happens to be an expert in this area and explained how the capacitor eliminates noise, basically smoothing out the power signal.

A 22,000uF capacitor can be had for $50 at Spruce and a 10,000uF is $7, so I asked him if that could be run in parallel, use two 10,000uF capacitors. The answer is yes.

If you run capacitors in series it cuts it in half, the opposite of batteries. Running two 6 volt batteries in series gives you 12 volts. If you run two 10,000uF capacitors in series it gives you 5,000uF

Capacitors have a Positive and Negative and are run inline, you connect the Negative lead to the Ground and the Positive to the Power/Positive wire. If you install the 22,000uF and still have noise, you can either get a bigger Capacitor or just add another. Using the leaded version, 2 wires, it's just a matter of twisting the wires together. I used a crimp connector and the then used a wire splice.

I planned on purchasing another 10,000uF, $7, but found another source for Capacitors. The 22,000uF screw terminal is less than $20 and the leaded version is less than $7. Here is the link. Select Leaded or Screw and then narrow the search by Capacitance and Volts.



If the 22,000uF isn't enough, I'll add the 10,000uF and am considering ordering a range of Capacitors, 5k, etc., to tune my system.

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Permalink Reply by Chumphol Sirinavin on November 19, 2010 at 9:25am
Nice shot of your airplane and occupants, Steve.
I can't even get my wife within 3 ft. of my airplanes.

Champ
Permalink Reply by Ralph Sanson on November 19, 2010 at 2:47pm
Agree Steve, need to identify the noise and then sort it slowly one step at a time - best to take lots of notes and data when doing this as it can be a long journey. The Xcom website has fairly simple procedures which go a long way to helping sort problems. They have a long association with Jabiru engines and small radios installed in recreational aircraft.

Jake, don't just buy the cheapest capacitor, they are made for many purposes, and an inappropriate one will explode, I know of 2 which have, and depending where you mount them, its not a pretty sight. You want a 40 volt rating, 105 deg C temperature and high pulse current ability component. I doubt that your noise will be caused by lack of a capacitor. I don't have one in my installation.

If you are across the Yahoo group, I wrote an article on dealing with radio noise, just click on the MS word document for the text.

http://groups.yahoo.com/group/jabiruengines/files/Radio%20noise/


I'm a RF tech and ham radio operator, flying is my other hobby.

Ralph
Permalink Reply by Jim Belcher on November 22, 2010 at 2:52pm

You might try paralleling the electrolytic cap with a lower valued (say, .1 uf) non-electrolytic capacitor. While the large value of the electrolytic will smooth out large variations in the power at lower frequencies, electrolytics sometimes have poor high frequency response. A non-electrolytic capacitor often works better at higher frequencies.

This is a result of the very way in which electrolytics are fabricated. A .1 uf non-electrolytic is cheap to try, and causes no harm, even if it doesn't happen to solve your problem.

Permalink Reply by Jake Reyna on August 5, 2013 at 10:06am

Levent, I used the 22mF from Mouser and that worked well. And I installed ferrite cores on just about everything coming through the firewall, including throttle cables, etc. The radio is now crystal clear. Mouser also sells ferrite cores. I also use ferrite cores on the headset jacks. I believe this is also recommended by Xcom, could be a Jabiru recommendation. Regardless, this is a simple solution, and worth the extra money.

Another issue was the crimps on the alternator wire connectors, the crimping tool crushed the protective coating and they basically fused together, no damage to the alternator. Now I make sure I wrap crimps with electrical tape or heat shrink, just in case.

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