Hi Mike,

If you presume that the EMP problem only travels down the antenna,
or the power cord, then you would possibly be right about the KWM2's
diode ring modulator. However, the KWM2 has virtually zip for shielding
in its low level circuitry. It has a slip on cover with holes punched
all over. I can easily hear its crystal HFO with the case shut.

Radios like the PRC-70, PRC-47, PRC-74 are all double shielded. First
the rf gasketed case comes off, then you have a chassis with rf gasketed
covers over all of the interesting modules... and of course, some of the
interesting modules have their own local shielding.

-Chuck, WA3UQV

Mike Knudsen wrote:
Note that the commonly available PRC-47 SSB transceiver is considered "EMP
hardened" by virtue of its tube fianl and RX tube RF amp. Those two are the
only tubes in the set, the rest is sorry-state. The whole radio is in a pretty
tight fitting metal box.

More to the point, the diodes used in the ring modulator of a KWM-2, being many
stages removed fromt he antenna or power line, are unlikely to be damaged by
any pulse coming in *electrically* from the outside.

The danger to such diodes (and the entire innards of a PRC-47) is from the EMP
wave itself, inducing voltages and currents in every little part and wire that
it travels thru.

Anyone know just where the PRC-47 is rated on the "hardness" scale?
--Mike K. AA1UK

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