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[aprssig] KPC-3+ with a Delta?

Stephen H. Smith wa8lmf2 at aol.com
Tue Jun 3 17:29:24 UTC 2008


John B. Leonard, Jr. wrote:
> I had a similar problem with a Motorola mobile.  The KPC3+ has a tranmit 
> level setting (I think it's "xmitlvl") that is used to change the deviation. 
> Once it was set from the default to a level much higher, it worked fine. 
> Bottom line:  there was no need to fiddle with the radio at all.
>
> 73
> w9jbl
>
>   

Commercial land-mobile radios (Motorola, the company formerly known as 
GE, etc) use mic levels that are enormously higher than typical ham 
gear.    Generations ago, the original land-mobile radios used 
telephone-type carbon mics that had an audio output on the order of a 
HALF VOLT. By contrast, most ham and CB gear uses UN-AMPLIFIED dynamic 
mics with outputs typically 5-10 millivolts. Over time, the carbon mics 
(with their poor audio quality) were replaced by dynamic and electret 
mics with vastly superior audio quality. To maintain plug compatibility, 
the replacement dynamics have always had built-in preamps to boost their 
output to the same .3 -.5V level as the old carbon mics. 

The net result is that the average commercial mic jack requires 100 
times (!) as much audio level to achieve 100% modulation as most ham mic 
jacks.   [Basically,  in commercial gear, the mic preamp is inside the 
mic while with ham gear the mic preamp is behind the front panel inside 
the radio.]   Fortunately the KPC3+ has an enormous audio output 
adjusting range, software-controllable from millivolts (for ham gear) to 
volts (for commercial gear).    (Earlier Kantronics and other make TNCs 
required moving a shorting jumper or changing a resistor inside the box 
to move between these two level ranges.)

Note that the commercial mic input level is what we would normally 
consider "line" level on computer sound cards,  home audio equipment and 
the 6-pin mini-DIN "data/packet" jack on many ham rigs. Ironically, the 
input level on commercial rigs is an almost perfect match, without 
attenuator pads, for the line audio in/out of PCs in applications like 
EchoLink, AGW Packet Engine, etc.




--

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com  --OR--   http://wa8lmf.net

NEW!   World Digipeater Map
  http://wa8lmf.net/APRSmaps

JavAPRS Filter Port 14580 Guide
  http://wa8lmf.net/aprs/JAVaprsFilters.htm

"APRS 101"  Explanation of APRS Path Selection & Digipeating
  http://wa8lmf.net/DigiPaths

Updated "Rev H" APRS            http://wa8lmf.net/aprs
Symbols Set for UI-View,
UIpoint and APRSplus:






--

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com  --OR--   http://wa8lmf.net

NEW!   World Digipeater Map
  http://wa8lmf.net/APRSmaps

JavAPRS Filter Port 14580 Guide
  http://wa8lmf.net/aprs/JAVaprsFilters.htm

"APRS 101"  Explanation of APRS Path Selection & Digipeating
  http://wa8lmf.net/DigiPaths

Updated "Rev H" APRS            http://wa8lmf.net/aprs
Symbols Set for UI-View,
UIpoint and APRSplus:






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