[CQ-Contest] band-pass filtering -- a new approach?

George Cutsogeorge w2vjn at rosenet.net
Fri Nov 9 11:54:43 EST 2001

The question was raised as to how much RF a modern radio can take.  Think
about it like this.  The RF input goes through an attenuator which uses 1/10
watt resistors and then goes to some switching diodes rated at maybe 50 mW.
Nuff said?

If the RF is limited to 1/10 watt (+20dBm) the radio will survive, but don't
we want to be able to hear signals on the second radio?  The FT-1000MP
blocks at 1/10 mW or -10 dBm.  The IMD is severe at -30 dBm.  An S9+20
signal is about -53 dBm.  etc., etc.  This was all covered in an NCJ article
a few years ago.  A good way to protect the front end as well as indicate
what's happening is with a low power pilot lamp.  Something rated at 50mA
and 1.5 volts is perfect.  It will light when the incident power approaches
the danger level and will blow out if it gets too high.  At normal signal
levels the attenuation it adds is 1 or 2 dB at most.

George, W2VJN

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