Topband: Preamp Shielding

Doug Waller NX4D at
Mon Mar 24 14:08:24 EST 2003


I have a directional phased endfire loops RX antenna that performs like a
beam on strong AM broadcast signals.  But for 160 meter weak signals in the
noise, I need 40 dB or so of preamp gain to overcome the antenna's  -50 dBi
gain (as reported by EZNEC).

Being in possession of two ICE 160m bandpass preamps, I tried connecting
them in series, but only got an S-7 noise, even with no antenna or antenna
coax attached.  Battery powering the preamps reduces the noise a couple of

I assume that the series connected preamps are either self-oscillating from
feedback, or are amplifying noise getting in through the metal cases.  One
way to get DC supply into preamps without allowing surface rf to pass
through the hole, is by using a Feedthru capacitor, about 10 mFd to choke
160m noise, but these seem to be no longer available.

If anyone has succeeded in getting a useful 40-45 dB of preamplification for
160m, either with one preamp or two, please let me know something to try.

73, Doug / NX4D

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