Yo! Troy:
Monday October 07 1996 21:31, Troy H. Cheek wrote to Bill Cheek:
 TC> Bill, since you've been active in both CB and scanners in the past, I
 TC> thought I'd ask your input on this...
 RS>> Um, as a matter of fact, i sometimes have the cb radio AND scanner
 RS>> on at the smae time...and both can be receiving two different freqs
 RS>> at the same time... i could be listening to the scanner, and key up
 RS>> on the cb mike and as far as i can tell, it isn't causing any
 RS>> damage, it just 'mutes' the scanner while i key up...
 TC> This, I've been afraid to try.  Oh, I've keyed up the mike accidentally 

 TC> time or two, but have never actually transmitted.
Keying the mic is......"transmitting".  Very much so.   :-)
 TC> I mean, the way I see it, a scanner's antenna input is used to seeing
 TC> something like microvolt signal levels coming in.  A 4 watt signal being
 TC> injected directly into the same input "should" blow the thing to Hell,
 TC> shouldn't it?
If you connected a coax between a transmitter and a receiver and then keyed 
the mic, that 4-watts would be dissipated in the front end of the receiver, 
typically in the shunt diodes, if any are present.  This would cause them to 
short out and protect the receiver even further.  If they didn't short out, 
then the input would be clamped to 0.6v, which the receiver is likely to be 
able to manage.
Otherwise, the input transformer and probably the preamplifier transistor are 
likely to blow.
It is a little different when the transmitter is not connected to the 
receiver. 4-watts out of the antenna, spread out over the spherical wavefront 
means only a few milliwatts into the receiver, even if the two are fairly 
close.  Let's suppose it's 100-mW.
Then we have 0.1-W across the 50-ohm input of the receiver.  Power equals 
E-squared divided by R, so:
   P  = E^2 / R
  E^2 = P / R
  E^2 = .1 / 50
  E^2 = .02
    E = .1414 volts or  141400 microvolts.
The receiver should be able to handle that.
Key word = "should"
Bill Cheek | Internet: bcheek@cts.com | Compu$erve: 74107,1176
Windows 95 Juggernaut Team | Microsoft MVP
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