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Radio audio troubles

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berkut13(at)berkut13.com
Guest

Posted: Wed Feb 14, 2007 8:09 pm Post subject: Radio audio troubles

Hi Gurus,



It's been awhile, but I hope all is well with you all.



I'm having audio issues with my new Becker 4201 #2 com and was wondering if

you could help.



The issue is the output audio from the radio whenever there is another radio

switched into the same output.  As soon as any other input is selected on

the audio panel at the same time, the com#2 volume goes very very low and is

overpowered. Sidetone during transmit seems un-affected as does the audio of

the other sources selected - only the Com2 audio drops down.  By

itself...the radio sounds fine, and operates properly.



The #1 com (iCom A200) works fine and is nice and loud with any number of

inputs selected on the audio panel (KA-134).  Adding additional inputs has

little to no affect on com1 volume.  It works great - as it should.



According to the KA-134 schematics, the only thing it's doing with the phone

outputs from the radios is mechanically switching them (no electronics)

together to a single output line to the intercom.  Because of this, I was

wondering if the impedance differences of the radios are a problem.

However, I have no real understanding of the magic involved here.



They are as follows according to the respective docs:

Com1 iCom - 500 ohms

Com2 Becker - 600 ohms

Eng mon - 560 ohms

Nav KN-53 - 500 ohms

RST Marker Receiver - unknown



I am still puzzled why Com1 has no issues with any number of other inputs,

and

Com2 does....impedance differences and all.



Any ideas?  I have schematics for the KA-134 if you want to see it...but for

this, it's just mechanical switches.



Thanks for any help!



James Redmon

Berkut13 N97TX

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nuckollsr(at)cox.net
Guest

Posted: Thu Feb 15, 2007 6:17 am Post subject: Radio audio troubles

At 10:08 PM 2/14/2007 -0600, you wrote:



 	  Quote: 	
		  



Hi Gurus,



It's been awhile, but I hope all is well with you all.



I'm having audio issues with my new Becker 4201 #2 com and was wondering if

you could help.



The issue is the output audio from the radio whenever there is another radio

switched into the same output.  As soon as any other input is selected on

the audio panel at the same time, the com#2 volume goes very very low and is

overpowered. Sidetone during transmit seems un-affected as does the audio of

the other sources selected - only the Com2 audio drops down.  By

itself...the radio sounds fine, and operates properly.



The #1 com (iCom A200) works fine and is nice and loud with any number of

inputs selected on the audio panel (KA-134).  Adding additional inputs has

little to no affect on com1 volume.  It works great - as it should.



According to the KA-134 schematics, the only thing it's doing with the phone

outputs from the radios is mechanically switching them (no electronics)

together to a single output line to the intercom.  Because of this, I was

wondering if the impedance differences of the radios are a problem.

However, I have no real understanding of the magic involved here.



They are as follows according to the respective docs:

Com1 iCom - 500 ohms

Com2 Becker - 600 ohms

Eng mon - 560 ohms

Nav KN-53 - 500 ohms

RST Marker Receiver - unknown


	


   Actually, those "output impedance" values are completely

   bogus. See:



http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf



   The true output impedance of any of these devices

   is considerably lower than the values stated. What

   they really mean to say is, "This product will produce

   rated output performance when presented with xxx ohms

   of LOAD.



   If the mental image I have from reading your words is

   coincident with your own, then it appears that something

   may be amiss in the audio isolation amplifier. The whole

   idea of such a device is ISOLATION. This means that adding,

   deleting or suffering a failure in any of the audio sources

   should have no effect on performance of remaining sources.



   Try swapping affected radios to different inputs to

   the amplifier and see if the symptoms swap with the radios

   or stay common to the switches on the amplifier.



    Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

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berkut13(at)berkut13.com
Guest

Posted: Thu Feb 15, 2007 3:49 pm Post subject: Radio audio troubles

Yup...switches with "ganged" inputs.  See below link for the schematic.

(300K .jpg)



http://www.berkut13.com/dloads/ka-134.jpg



I'm glad you attached Dan's reply, I never received it.  I guess I can

perform surgery on the input lines and install a 220-ohm resistor on each.



Yeah, it's a hunk of junk King!  I wish I had never installed it...but it's

far worse to try to extract it and start over now.  Anyone know if the VAL

(same size) AP-100 has a isolation circuit built in?  It might become a 

"throw

money at it" solution if the resistors don't help.



What I don't understand is why Com1 (iCom) can be "switched" in with all the

other inputs with no adverse affects.  But, the com2 (Becker) can't - ANY

input source that's switches in takes the Becker to almost zero and, of

course, when the volume is turned all the way up it's all distorted.  Add

all you want to the iCom and the blend in just fine.  Is that what John is

suggesting might be cause by the iCom possibly having a significantly lower

impedance than the other radios?



I can also tell you that the iCom's output is very robust compared to the

other radios.  It's quite loud, deep and clear with very little turn of the

volume knob - very sensitive.  Not sure that says anything other that it's

got a good amp on it, but I'll put that out there too.



Again, thanks for all the help!



James

---

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