[Boatanchors] [BoatAnchors] How to Protect from Nearby Transmitter?

[Donald Davis]

The best bet is to shield the xmtr output and install a balun or unun to
kill the rf in the shack.  The loop antenna is hi-q so it is susceptible to
strong near-fields.  I did a lot of LW Beacon DXing in Georgia, with
lightning strikes for 100 days per  years.  I bot lots of FETs for the loop.
Finally got it well grounded when not operating and that cured it.  You
might try a small TO-5 latching relay  and short the loop whenever you're
not receiving.  FETs and hi-speed diodes may not be fast enough, you might
try power MOSFETs with protection layer with fast turn-on and fast recovery.
Relays are slower, so you'd have to ensure that xmit is clamped after the
relay has fully transitioned.  

73 de don ad6ph 

-----Original Message-----
From: BoatAnchors [mailto:boatanchors-bounces at theporch.com] On Behalf Of
David Stinson via BoatAnchors
Sent: Monday, December 04, 2017 3:37 AM
To: boatanchors at mailman.qth.net; milsurplus at mailman.qth.net
Subject: [BoatAnchors] How to Protect from Nearby Transmitter?

This is a Palomar LP-1 loop amplifier.  It works well listening to Longwave.
The last time I transmitted near it (75 mtrs), it blew the FETs.
The diodes didn't do the job.  How can I protect the amplifier from a nearby
472 KC transmitter?
Use a fast MOSFET to short the loop on transmit?

73 OM DE Dave AB5S