[aprssig] KPC-3+ with a Delta?
Stephen H. Smith
wa8lmf2 at aol.com
Tue Jun 3 13:29:24 EDT 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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