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one accessory affecting another ??????

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kgmjeric

Joined: 28 Aug 2010
Posts: 3

Posted: Wed Sep 01, 2010 7:30 pm Post subject: one accessory affecting another ??????

is it common for an intercom to receive different power level based on the radio being turned on or off?   they share a common power wire.   



RADIO turned OFF the intercom led is inbetween red and green and defaulting to co pilot side only



RADIO turned ON the intercom led is bright green and functioning well



when i say turned on or off I mean that the knob on the radio is turned to the off position or on position the power wire stays hot always

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nuckolls.bob(at)aeroelect
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Posted: Thu Sep 02, 2010 6:18 am Post subject: one accessory affecting another ??????

At 10:30 PM 9/1/2010, you wrote:




is it common for an intercom to receive different power level based 

on the radio being turned on or off?   they share a common power wire.



RADIO turned OFF the intercom led is inbetween red and green and 

defaulting to co pilot side only



RADIO turned ON the intercom led is bright green and functioning well



when i say turned on or off I mean that the knob on the radio is 

turned to the off position or on position the power wire stays hot always

     Your narration has the "smell" of a noise issue.

     I'm not familiar with the 'red/green' thing on the

     intercom and you don't say what kind of radio is

     involved . . . but here's a WAG.



     Many modern radios have inverters to supply special

     power for operation of LCD and/or glow-discharge

     displays. These are potential antagonists for noise.

     Will they PROBABLY meet DO-160 requirements for how

     much noise is pushed back onto the power line, the

     intercom MIGHT be unusually susceptible. Try operating

     the intercom from a separate 12v source, like a

     test battery as described in the noise trouble shooting

     section of The 'Connection.



     If this makes the symptoms go away, consider adding

     a line noise filter in the +14v supply to the intercom.

     We have a filter you can try . . . if it doesn't do

     the job, you can return it.



     Bob . . .

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kgmjeric

Joined: 28 Aug 2010
Posts: 3

Posted: Thu Sep 02, 2010 6:32 am Post subject: Re: one accessory affecting another ??????

I am not having the problem with the radio turned on and it pushing backfeeding through the power line but that the intercom will only perform with the radio turned ON

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Fri Sep 03, 2010 3:51 am Post subject: Re: one accessory affecting another ??????

Just my two cents worth but it is important to understand that many regulated power supplies and regulator ICs require a minimum load (current draw) before they will regulate. 



It is possible that the intercom does not draw enough current to do the job and a load ohm resistor across the input power but after the on/off switch might be required.



This load resistor is an important circuit element even with LM317 regulators. They specify a Min Load Current of a few milliamps, but other supplies can be several tens of milliamps or more.

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
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