[CQ-Contest] What RF voltage OK at Rx in SO2R?

k8cc k8cc at mediaone.net
Thu Sep 27 00:31:04 EDT 2001

At 09:42 AM 9/26/01 +0000, Marijan Miletic, S56A wrote:
>G4BUO circuit with 4 diodes would limit at 3 V RF peaks.  This equals 
>about 50 mW of power distributed over the wide frequency range.
>In order to reach back to the antenna, RF should go thru bulb which has 
>certain inductance and makes a nice lowpass filter.
>However, additional bandpass filters are strongly recommended.

A small light bulb does not have enough inductance to form a low pass 
filter.  Most light bulbs I've seen only have two turns, maybe 5 mm in 
diameter.  This does not form enough inductance for a low pass filter.

As further proof, at WRTC 1996 I had a minibox with a small light bulb in 
it which we put in series with antenna to the multiplier radio until we 
were confident of the isolation between antennas.  This bulb introduced no 
noticable loss.

I forgot to finish my story with the 40M quad.  I took the switchbox down 
and soldered a .01 uF ceramic disk capacitor across the diode and the 
problem was solved.



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