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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.
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.
Replies to This Discussion
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Permalink Reply by Louis W. Ott on
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Hi Jake,
You may want to try a ferrite core inductor. Put one of these in your power lead on the power source side of the capacitor(s). The clip on type can be clipped over the power wire. If you use the ferrite tube type, wind two or three turns of the power wire through the tube, then on to the capacitor, and to your radio. The inductor will inhibit rapid (microseconds) current change while the capacitor(s) inhibit rapid voltage change. They work together to make a low pass filter. If you have a "glass cockpit" unit, you may want to put one of the ferrite inductors in the power lead to that unit. Noise from the glass cockpit unit may be leaking out the power lead into your power system.
http://www.aircraftspruce.com/catalog/inpages/mglferritesupress.php
http://www.aircraftspruce.com/catalog/inpages/ferriteclip.php
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Permalink Reply by Jake Reyna on
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Thanks Louie!
I hope to be zooming by your house in the near future :-)
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Alright! I will head to the airport and listen for a Jabiru 3300. We can get a sandwich at the Baldwin Saloon.
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Permalink Reply by Juan Vega on
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jAKE,
You can do more also on the engine side by using, resistor plugs, resistor plug wires, shielded alternator.
Juan
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If you have a jabiru 3300 like it says below, try using D9EA Resistro plugs by NGK.
They work for mine. PLus a big ass toroidal coil behind the radio.
Juan
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Juan, thanks for the info. I'm going to try the correct capacitor ($10) recommended by XCom first and then follow the path you suggest.
I spoke with Jim at Jabiru Pacific, he uses the Garmin SL-30 and doesn't have any issues, so the radio might be part of the problem and I wonder if metal airplanes aggravate the issue. Jim is flying a Jabiru J-200.
Thanks
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Permalink Reply by Phill Barnes on
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Hi Jake
The following is a pasted copy from the Jab Aus website. Most of my electrical equipment was purchased directly from them so I also used the noise supresssor for the avoinics bus and ferrite cores for all wiring bundles that they use on their aircraft. I hope one of these fixes solves your problems.
Phill
Testing>Troubleshooting VHF noise issues
Objectives of this task:
To offer solutions for various common noise issues that may affect VHF comms.
In a metal aircraft the fuselage is usually earthed and thus it tends to shield the radios (VHF,
HF) from induced noise, however with the Jabiru being constructed from glass fibre other
techniques must be employed to cure any unwanted electrical noise. This task will offer
solutions for common noise problems. Some aircraft will suffer no noise problems at all while
others may have one or several noise problems, so use only what you need from this task.
Noise types
There are 2 types of electrical noise that can affect an aircraft radio:
DC Ripple refers to the quality of the power (DC = Direct Current) that is supplied to the
aircraft radio. The power can be filtered with a suppressor type filter to reduce noise.
RFI refers to radiated energy from various electrical sources such as the ignition or alternator
that is induced into the wiring harness and then picked up by the radio. The most useful fix
for this is to fit ferrite clamp filters, either as close to the source of the noise as possible or on
the radio input coaxial cables.
Equipment
Suppressor type filters
An “alternator suppressor” filter, purchased from an auto electrical supplier and fitted behind
the panel between the earth busbar and the avionics busbar, will often clean up any residual
DC ripple noise in the power supply that has got past the standard power filter. Use this if you
have a small but continuous background noise in your headset.
Ferrite clamp filters
These are readily available in various sizes at electronics supply shops and can be seen on
computer monitor cables and some telephone cables. The filtering effect can be multiplied by
looping the wire through the filter once (4x) or twice (16x) so if you have sufficient wire
length then the more loops the better generally, up to a maximum of 2 loops.
Noise sources and solutions
Flap motor
The flap motor may start to become audible in your headset once it has some use and the
brushes have started to wear. This will be heard as a harsh noise when the flaps are being
extended and retracted. Fit a ferrite clamp filter to each flap power wire as close to the flap
motor as possible and loop each wire through each filter once.
Magneto earth leads
A single wire from each magneto coil is routed back to each MAG switch and is connected to
earth to stop the engine. Indication is a light “ticking” noise that speeds up when engine revs
are increased.
While the engine is running the wires are not earthed and they can radiate noise that can easily
be stopped by clipping a ferrite clamp filter onto each wire just inside the firewall, before the
multi-pin plug. If there is sufficient wire to loop it once though the filter then do so.
Jabiru J ALL Constructors Manual
Testing>Troubleshooting VHF noise issues
2 of 2 Thursday, August 6, 2009
Alternator
The alternator wires will radiate a certain amount of noise, however if you have followed the
instructions in the Post-Paint>Electrical Wiring task and twisted the pair over the full length,
the effect of that twisting will be to cancel the noise at source. If not then unclip the wires
from the wiring harness and twist them around each other for their full length.
Strobe
Test for strobe noise by turning the strobes off and back on. If this is a problem use a ferrite
clamp filter around the strobe power supply wiring. Route strobe wiring as far away from the
rest of the aircraft wiring harness as possible to prevent induced or “spill over” noise.
Beacon
Test by turning the beacon off and back on. If this is a problem use a ferrite clamp filter
around the beacon power supply wiring, with each wire looped though the filter if possible.
Transponder
The transponder sends out a strong signal from it’s antenna that the radio can sometimes
“hear” and the effect is to make VHF transmissions weaker and produce crackling sounds
with incoming VHF calls. This is often the cause of reduced VHF range or rapid drop off in
quality with distance. Test by turning the transponder off and back on after several minutes.
Route the transponder and VHF coaxial cables as far away from each other as possible behind
the panel in the cable bundle from the panel down to the console, and fit a ferrite clamp filter
over each coaxial cable (VHF, transponder) as close to each unit as possible. Hold the filter in
place with a small zip tie around the cable to stop the filter from slipping down if required.
Each coaxial cable must be free of any sharp bends because these can cause the earth
shielding in the cable to open slightly and reduce the level of signal rejection, so check your
cable routing carefully and correct any sharp bends.
In some cases the proximity of the VHF and the transponder units in the panel can cause
signal bleed between the units. If possible locate the transponder as far away in the panel from
the VHF unit(s) as possible. This signal bleed reduces at the square of the distance so a small
change (movement away) is all that is usually needed.
In rare but extreme cases relocating the transponder antenna towards the rear of the fuselage,
well away from the VHF unit(s), has fixed the problem.
Electric turn and bank indicator (ETI)
The electric motor that runs the gyroscope in the ETI may return noise into the avionics – test
for this by turning the ETI switch off and on. If this is a problem consider rewiring the ETI
power supply away from the avionics busbar to a separate, different 5 amp circuit breaker.
Microphone noise
If you can hear noise in your headset each time that you press the transmit button, fit a small
ferrite clamp filter to each microphone wire in each headset jack.
In 4 seaters with 2 VHF comms and 2 antennae some noise will be radiated from the internal
antenna in the empennage that may be picked up by the rear headset jacks. Ferrite clamp
filters around the microphone wires, with each wire looped through the filter once, will
usually clean this up. If the problem persists it may be necessary to make a small earth
shielded cover for each set of headset jacks in the rear seats.
This completes the Troubleshooting VHF noise issues task.
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Phill, I hadn't thought of visiting the Jabiru website for a solution. Thanks!
Jake
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I had a local pilot suggest the use of more shielded wire. It appears to be another lesson learned, late ;-) Thanks for the link.
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Permalink Reply by Bob Pustell on
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I would not get too apologetic, Jake. Shielded wire everywhere is overkill. Also, shielded wire weighs a lot more than normal wire. There are a few places where shielded wire is appropriate (in the intercom and headset/mike wiring, for instance) but for the most part it adds weight and expense without any benefit. Properly installed, non-shielded wiring works fine for most parts of the electrical system. The key, I guess, is learning where it is good to use it and where you do not need it.
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I was thinking of replacing the headset wiring with shielded after installing the recommended capacitors and ferrite inductors. I'll go the easy path first.
The lesson learned is to have used shielded wire on the radio harness. I am thinking of adding capacitors to the power lines to the other instruments, to smooth out the power, now that I found a inexpensive source.
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Steve, I did bring the manuals back with me, to read :-) I built my harness from the XCOM kit, it doesn't have shielded wires. Since I didn't have the Capacitor installed, adjusting the squelch didn't help.
The temporary solution was to throttle back to 2,000 rpm or less and the noise would go away and I was able to communicate in the pattern. It was ugly on takeoff.
Thanks for the Narco update.
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