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
|
|||
|
|||
Questions on installing an intercom
I have an electrical/audio question. The intercom I'm installing has a
wiring diagram that shows the sleeve terminal of the phones and mic connected to the shield at the radio end. This seems pretty typical. My question: is it okay practice to use the wiring shield as one of the conductors? In other words, can I use 2-conductor shielded wire for stereo headphones (left, right, and shield for ground) or should I buy 3-conductor so the sleeve terminal has its own wire inside the shield? I ask because both the sleeve and the shield get tied to ground at the radio end anyway. Also, should I use a separate wire for the mic audio, or can all of the conductors run inside the same shielded wire using a common ground? Thanks, Craig. |
#2
|
|||
|
|||
Questions on installing an intercom
|
#3
|
|||
|
|||
Questions on installing an intercom
On Feb 28, 6:42 pm, wrote:
I have an electrical/audio question. The intercom I'm installing has a wiring diagram that shows the sleeve terminal of the phones and mic connected to the shield at the radio end. This seems pretty typical. My question: is it okay practice to use the wiring shield as one of the conductors? Yes. The fact that the return current from the phones is flowing down the shield does not adversely affect the electrostatic function of the shield at all. If it did, the manufacturer of the phones wouldn't do it this way either! The return current in the shield and the outgoing current in the center create cancelling fields; no external field is generated. Nor is any external field able to create a voltage difference inside the shielded cable by reciprocity. In other words, can I use 2-conductor shielded wire Yes. for stereo headphones (left, right, and shield for ground) or should I buy 3-conductor so the sleeve terminal has its own wire inside the shield? I ask because both the sleeve and the shield get tied to ground at the radio end anyway. 3 wire not necessary, see above. Also, should I use a separate wire for the mic audio, or can all of the conductors run inside the same shielded wire using a common ground? Do NOT run the phone line in the same lines as the mic. Some intercoms will oscillate if you do this. It is usually OK to run the keyline in the same shield as the mic line, so have lots of the 2 conductor. You can run both channels of the phones in a single shielded wire; you can run the mic and key in the same shielded wire. But not all. What is very important is to isolate the mic and phone jacks where they mount to the airframe. Use shoulder insulating washers, available from spruce. What WILL destroy the effect of the shield is to ground the far end to something like the airframe. Creates a ground loop and alternator currents (which have an AC component) flowing to things like the nav lights thru the airframe will have a small drop and flow in the shield of your mic line which you absolutely do not want. You avoid this by insulating the jacks so no ground current from any source can flow into them. Oh, and use the correct aircraft wire, not rat shack. There's lots of 2 conductor 27500 out there. The manufacturer's diagram will probably reflect all this. Bill Hale EE A&P Thanks, Craig. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Installing an ELT antenna. | [email protected] | Soaring | 22 | September 27th 05 11:09 PM |
Installing a wood prop... | SteveR | Home Built | 19 | July 24th 05 06:42 AM |
Anybody installing tri-band (406MHz) ELTs? | Michelle P | Instrument Flight Rules | 0 | July 4th 05 09:10 PM |
Installing ALL of FS5.1 from CD to HD | Greg.S | Simulators | 3 | October 8th 04 09:56 PM |
fs2004 INSTALLING QUSTION | Tlewis95 | Simulators | 1 | December 26th 03 09:59 AM |