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<DIV><FONT face=Arial size=2>If the problem is not a PL tone you could try or
verify:</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>1. Make sure the GND signal between the TNC audio
and the radio microphone jack is disconnected in the connector on the microphone
side so it does not make a connection from the TNC GND to the microphone GND on
the radio. This is important for several reasons.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>2. Make sure the GND from the power connector from
the TNC and the GND from the power connector on the radio are connected at the
same point at the power supply. This will provide your single point ground
source at the power supply.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>3. This step is re-iterated from step #1. Make sure
the TNC GND from the 5-pin DIN connector and the GND on the radio microphone
connector are not connected.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Now if you have other equipment connected to the
radio, power supply, or TNC all bets are off without a full description of what
is connected and how it is connected.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>73's de Tim - N8DEU</FONT></DIV>
<DIV><FONT face=Arial size=2>Huntsville, Alabama</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=pagreen@gmail.com href="mailto:pagreen@gmail.com">Patrick Green</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=aprssig@lists.tapr.org
href="mailto:aprssig@lists.tapr.org">TAPR APRS Mailing List</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, February 27, 2006 9:48
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [aprssig] Problems with hum on
TX audio.</DIV>
<DIV><BR></DIV>Hi All,<BR><BR> I've changed radios out at KA9SCF-15 and
in doing so, acquired this nasty hum on the TXA (at any transmit power
level). There is nothing superimposed on the hum like a radio station,
etc. This radio is far more sensitive on TXA than the previous and had
to reduce the TXA to get it to match the 281. When I labbed this
at home 1st there was no hum at all. Here's the run down of the change and the
things that I've tried so far:<BR><BR>Old radio: Icom IC-281H<BR>New radio:
Icom IC-2200H<BR><BR>The TNC is an MFJ-1270C with a cube powersupply that came
with it.<BR>The radio is hooked up to a old Motorola repeater power
supply.<BR>The antenna system is on the same ground as the power
supply.<BR>The cable is made for an ICOM-2000H and converted to the 2200H
using a home brew jumper.<BR><BR>Things I've tried to isolate the
problem:<BR><BR>Changed the cube power supply to the TNC to one that had more
amps. No change<BR>Changed the power source of the TNC to a battery
pack. No change<BR>Changed the TNC to an MFJ-1270B and adjusted the
TXA. No change<BR>Changed the wiring jumper to use Mic ground instead of
chassis ground. No change.<BR>Used the cable wired for the 2000 into the
radio. No change (I get no RXA which is why I needed the
jumper)<BR><BR>Things that are on the list to try yet:<BR><BR>Using toroids on
the cable to the radio to the TNC (where the TXA is carried).<BR>Changing the
radio power supply (this wouldn't be permanent).<BR>Using the IC-2000H to
test. (the cable was made for this radio initially and had no hum but
not tested at the digi site)<BR><BR>Can I add a resistor or something to the
line to require more drive from the TNC thus reducing the noise coming in on
the line and placing it close to the radio? What value would I
use?<BR><BR>Thanks for any help.<BR><BR>73 de Pat --- KA9SCF.<BR>
<P>
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