If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
Lowering cockpit RF interference
Hello all EEs.
What is standard operating procedure for when and where to use shielded wire in cockpit wiring? What is standard operating procedure for when and where to use ferrite sleeves? Do both the positive and negative lead need to pass through the ferrite sleeve? Thanks for the education. |
#2
|
|||
|
|||
Lowering cockpit RF interference
wrote:
Hello all EEs. What is standard operating procedure for when and where to use shielded wire in cockpit wiring? What is standard operating procedure for when and where to use ferrite sleeves? Do both the positive and negative lead need to pass through the ferrite sleeve? Thanks for the education. It can all be a bit trial and error, but http://audiosystemsgroup.com/SAC0305Ferrites.pdf gives some of the theory and practical aspects of it. Key points: - mount "close" to interference source (close = less than 1/20th of the wavelength) - mount "close" to whatever is being affected by the interference - multiple loops are better, usually - resonance can cause surprises; be prepared to experiment - any piece of wire can be an antenna, including the cable shields |
#3
|
|||
|
|||
Lowering cockpit RF interference
On Friday, December 14, 2012 11:04:39 AM UTC-8, wrote:
Hello all EEs. What is standard operating procedure for when and where to use shielded wire in cockpit wiring? What is standard operating procedure for when and where to use ferrite sleeves? Do both the positive and negative lead need to pass through the ferrite sleeve? Thanks for the education. What equipment do you have in the cockpit,specify all equipment, Make and Model? What kind on interference are you getting? Richard www.craggyaero.com |
#4
|
|||
|
|||
Lowering cockpit RF interference
|
#5
|
|||
|
|||
Lowering cockpit RF interference
|
#6
|
|||
|
|||
Lowering cockpit RF interference
On Fri, 14 Dec 2012 14:24:28 -0800, Eric Greenwell wrote:
Most electrical noise problems come from specific problems in the installation, and can be tough to track down. Ferrites can be an easy fix sometimes; shielded wiring isn't so easy to install, and it's often hard for even an experienced EE or technician to know exactly which cable(s) is the problem and should be replaced. The only electrical noise problem I've had was when I installed a 28v T&B which was powered of the glider's 12v supply with a solid state 12v-28v DC-DC converter. The solution was to put an electrolytic capacitor across the 12V supply to the converter. This was a specialized noise cancelling capacitor and IIRC it is 150 uF with a 1.5A transient current capacity. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#7
|
|||
|
|||
Lowering cockpit RF interference
I had the same problem, though with a 12v T&B, and used a ferrit in the
power lead to solve it. The only electrical noise problem I've had was when I installed a 28v T&B which was powered of the glider's 12v supply with a solid state 12v-28v DC-DC converter. The solution was to put an electrolytic capacitor across the 12V supply to the converter. This was a specialized noise cancelling capacitor and IIRC it is 150 uF with a 1.5A transient current capacity. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#8
|
|||
|
|||
Lowering cockpit RF interference
On Sat, 15 Dec 2012 11:49:06 -0700, Dan Marotta wrote:
I had the same problem, though with a 12v T&B, and used a ferrit in the power lead to solve it. I think I tried a ferrite core on the 12v side of the voltage converter without success and then remembered that Maplins (the UK equivalent of RadioShack) had these capacitors at a reasonable price. Better yet it was easy to fit: I just soldered it across the T&B power switch. The only electrical noise problem I've had was when I installed a 28v T&B which was powered of the glider's 12v supply with a solid state 12v-28v DC-DC converter. The solution was to put an electrolytic capacitor across the 12V supply to the converter. This was a specialized noise cancelling capacitor and IIRC it is 150 uF with a 1.5A transient current capacity. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#9
|
|||
|
|||
Lowering cockpit RF interference
On Saturday, December 15, 2012 2:32:26 PM UTC-8, Martin Gregorie wrote:
On Sat, 15 Dec 2012 11:49:06 -0700, Dan Marotta wrote: I think I tried a ferrite core on the 12v side of the voltage converter without success and then remembered that Maplins (the UK equivalent of RadioShack) had these capacitors at a reasonable price. Better yet it was easy to fit: I just soldered it across the T&B power switch. martin@ | Martin Gregorie gregorie. | Essex, UK org A couple of thoughts here . . . When you say you soldered it "across" the power switch, that might lead one to assume you soldered it to the two terminals of your switch, i.e. in parallel with the switch contacts). Normally a filter capacitor would be connected across the power leads, i.e. from + to -. While a filter inductor (such as a ferrite) is connected in series. When trouble shooting RFI, it helps to be able to quantify results. If it's interferance on comm freqencies, a hand held radio can be useful - squelch off, and distance away from suspected RFI source as appropriate one can use the handheld as a field strength meter for radiated interferance. This is not so much use when dealing with closely spaced instruments on the panel where one is causing problems with another (LNAV did that to Comm on one of previous glider). There, just slapping in clamp-ferrites did the job. If you have enough slack in wiring leads, and the size of the ferrite allows, you get almost double the iductance for loopiing the wire/s through the ferrite twice, (or even more for 3 times etc). Sometimes adding a capacitor in concert with the ferrite helps even more, especially when noise is coupling via power leads (ferrite or inductor in series and cap across the wires in parallel to form a classic pi filter). Ferrites are not all the same, they have a frequency band at which they will be most effective. Same thing with the size of capacitors used in filtering apps. (do a search on inductive and capacitive reactance and resonant frequecy). In the U.S., Digi-Key is one good source for ferrites etc. bumper zz Minden, NV bumper |
#10
|
|||
|
|||
Lowering cockpit RF interference
Your question is less about "I have a problem and want to fix it." versus, "I don't want any problems in the first place. What are the best practices to follow?"
Literally the only interference problem I have every had was a vario that deflected when I keyed the transceiver. Solution: replace the vario. I must live a blessed life. This has also been in pure gliders only so I don't have to worry about ignition noise which is by far the worse culprit for interference. However, new electronics run at some high frequencies (1Mhz processors are sloooow these days), so interference can happen. So back to what I do to prevent problems in the first place. 1) Start with QUALITY - Components, wiring, terminals, switches, etc. Buy from an aviation source like Wicks or Aircraft Spruce. Radio Shack and ACE Hardware DO NOT have aviation aisles. Modern avionics seldom seem to create issues as they have to pass some pretty stringent testing to be certified. Step away from anything still using crystals (are they still legal?). 2) Coax for microphones and antennas. But every microphone and antenna already comes with coax. The more important bit is making sure that the shield has a good ground at the avionics end. A good BNC connection for the antenna (have someone knowledgeable help). Many transceivers have a separate ground pin for the microphone - use it! 3) Ferrite beads - While my EE specialty is not in the RF spectrum (get it?), putting these on doesn't hurt and might help ... so I use them. As someone in this thread said, run both the +/- wires through the bead twice if you have the slack. Non-split beads are generally better than split beads. The trick is to prevent high frequency noise from one device getting into another device through your power bus. 4) Air gaps - Wires that might have data flowing through them, like a GPS to a PDA, can induce noise into another wire running right along side of it in a bundle. So separate any suspect wires from one another. 5) Grounding - Ground all your devices to a single common location as close to the electronics as possible, including the negative side of the battery.. Even ground the metal stick, push tubes, etc, if possible. Good luck, John |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Trying again: Collings Foundation B-17 at Newcastle Airport inDelaware - B-17 cockpit.jpg - B-17 cockpit.jpg (1/5) | Jim Breckenridge | Aviation Photos | 1 | August 30th 08 07:36 PM |
Trying again: Collings Foundation B-17 at Newcastle Airport in Delaware - B-17 cockpit.jpg - B-17 cockpit.jpg (0/5) | Go-dot | Aviation Photos | 0 | August 28th 08 11:39 PM |
Wings of Freedom B-17 Wilmington, DE - B-17 cockpit.jpg - B-17 cockpit.jpg (0/5) | Go-dot | Aviation Photos | 0 | August 28th 08 09:37 PM |
Retraction (lowering?) assist springs on V2C | [email protected] | Soaring | 1 | January 5th 06 05:20 PM |
Lowering Stall | Dick | Home Built | 7 | December 25th 03 03:19 PM |