[ARC5] SM-30 URM-14

[WA5CAB at cs.com]

Wayne,

No.  As originally built, it is NOT for testing microphones.  It is for 
testing AM or SSB transmitters through their carbon mic jacks.  The input 
impedance taps are to allow matching the audio signal generator or other tone 
source's output impedance.  For example, the output impedance of the TS-382(*) 
is 1000 ohms.  

As originally built, if you connect the output to the mic jack on the 
transmitter, plug a carbon microphone into it and depress the PTT switch on the 
microphone, you will NOT key the transmitter.  But the meter won't move 
anyway and you will not get any modulation out of the transmitter because there 
is no bias current supply for the microphone.

The jack labled "Microphone Current" is misleading.  What you are measuring 
is the current that the transmitter could supply were you to plug a 
microphone directly into the transmitter and IFF the microphone resistance happened 
to be 82 ohms.  So all that it really does is confirm that the mic bias 
supply from the transmitter is active.

My modification to one of the units that I have turns it into a microphone 
tester of sorts.  But the mic still will neither key nor modulate a 
transmitter.  That wasn't my intent.  Schematic of mods available to anyone who 
wants it.  Parts required are DPDT Switch, 12 V Lamp, 3.6 (or thereabouts) ohm 
resistor, and 9V Battery.  It will also test the microphone side of handsets 
like TS-13 and TS-15.

In a message dated 03/20/2017 10:21:28 AM Central Daylight Time, 
releazer at earthlink.net writes: 
> Yes, that is it!  I think "microphone simulator" is an odd name for the 
> critter.  A "transmitter simulator" for a microphone would make sense.  A 
> "tire simulator" for a wheel would not make much sense, either.
>   
>  Monitoring carbon mike current is about the only thing I could imagine it 
> would be good for.   It includes a schematic inside the front cover.  I 
> see that it has a variable input impedance, 500, 1000, or 5000.      
>  
>  Thanks,
> 
> Wayne
>  WB5WSV
> 

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
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