Strange MOX behavior

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  • Updated 1 year ago
MOX is working differently for two different mics.  Here's the setup:

Flex mic and headset mic fed into a switchbox that simply switches the microphone line between the two mics into the radio.  A foot switch is also fed into the switchbox and tied into the PTT line.  

Using the Flex mic (FHM-1), I get audio using its own PTT switch or the foot switch, but NO audio when I use the MOX pushbutton in SmartSDR or in FRStack.  When I switch to the headset mic I get audio using the foot switch AND the MOX pushbutton in SmartSDR and in FRStack.  Both mics feed into the same audio in line in the Foster plug!  

I am NOT pushing the PTT on the Flex mic when trying to use MOX, but the PTT switch is a SPST that uses only NO and C, it's not switching the audio line from the element.  

So why does MOX work when the headset mic is switched in but not when the Flex mic element is switched in?  

BTW.  I'm doing this because the PTT switch in the Flex mic is becoming erratic and as it makes/breaks while talking it's causing a lot of clicking sounds.  I already ordered a replacement Heil mic but just want to know why the Flex mic and headset mic are behaving differently for MOX operation.  

Dick
KF5SA
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Dick B

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Posted 1 year ago

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Tim - W4TME, Customer Experience Manager

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Which PTT input are you using?  There are three of them on the radio.
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Dick B

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I'm using the PTT in the front panel Foster connector.  A line runs from the front panel to my mic switch box, which switches only the audio line between the Flex mic and my headset mic.  
(Edited)
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Tim - W4TME, Customer Experience Manager

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OK.  That is strange.  Do they work correctly if they are directly connected to the Foster connector without the switch box?
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Dick B

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The Flex mic still has no audio using MOX when plugged directly into the 6300 and not pushing its PTT.  The Heil headset DOES have audio when plugged directly in using MOX. 

I made a 1/8" to Foster adapter for the Heil Proset iC that has a 2.2K resistor between pins 2 and 8, and use a Mic profile appropriate for the Icom mic element (bias On).  

Just for completeness, the adapter plug and switch box have pins 5 and 7 grounded.  

Do you have a schematic for the FHM-1?  I can't find one online and am using one for the Yaesu MH-31, which appears to have no connection between the PTT switch and the audio line.  I know some mics switch the audio line also using a double-pole PTT switch but the FHM-1 does not appear to do that.  
(Edited)
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Tim - W4TME, Customer Experience Manager

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OK.  I need to get the materials together to test this.
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Dick B

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Tim, I just replaced the FHM-1 with a Heil HMM and it behaves the same way ... no audio using MOX without pushing PTT... BUT if I switch to VOX I get audio without pressing PTT when I talk!  

This seems to rule out any differences due to Mic Profiles.  The Heil Proset iC headset still has audio using MOX.