On 08 Sep 2003 02:51:30 GMT, r (Mike Knudsen)
wrote:

Note that the commonly available PRC-47 SSB transceiver is considered "EMP
hardened"

PRC-47, or PRC-74?

I had forgotten about that radio but now I remember it from my old
days as a field radio repairman (MOS 31E20) in the Army in 1967-1970.

I thought it was a PRC-74, but that was a long time ago...

Rick WA1RKT

In article ,
r (Mike Knudsen) writes:

Pretty sure both the Nationals are all tubes -- even the balanced modulator
is
a 7360 beam deflection tube. Also, the PS boxes include the speaker.

The NCX-5 has quite a bit of solidstate in it. The NCX-3 does not.

They are very different rigs under the hood.

The 80/40/20 NCX-3 was replaced by the 80-40-20-15-10 "National 200". Nice
looking little rig but not very popular.

73 de Jim, N2EY

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

Oscar loves trash, but hates Spam! Delete him to reply to me.

wrote in message
...
On Sun, 07 Sep 2003 02:44:05 GMT, "Chas" wrote:

Hi Rick! The SBEs were solid state too(driver & finals were tube), so
if your critera was an internal power supply & all tube, the Swan is your
only choice (as far as my memory goes).

Thanks, Chuck. The internal power supply and/or the small size are
only preferences, that I can live without. The only hard requirement
is the all-tube design.

Go with the KWM-2.

Yeah, I'm beginning to reach that conclusion. I've been checking a
few prices on eBay and qrz.com and they certainly are proud of 'em ...
from $300-$400 for a beater that needs a lot of work to $1200-$1500
for a -2A that is claimed to be in perfect condition.

Are things like tubes and shop manuals more or less readily available?

Guess it's time to start haunting the 75-meter swap nets and the flea
markets. Hoss Traders is coming up here in New Hampshire early next
month, I think. Any other big, well-known and well-attended flea
markets coming up anywhere in the Northeast or mid-Atlantic states,
west to about Ohio?

Rick WA1RKT

Nobody has even mentioned the Heathkit series. HW/SB-100/102/etc. All tube
type.

Dan/W4NTI

and frankly, using nukes to create EMP would be the most "humane" and
attractive option to an opfor that I can recognize. take out all the
"Bygollians" infrastructure and ability to react and defend, and watch
'em kill each other off in paranoia, wackiness, disruption of food
supply due to loss of the toys, and harvest the spoils without any nasty
radiation in a few months.

think about it. clear out the power grid, communications, personal
electronics, emergency services command and control systems... cars and
trucks can't be used because the engine computers and coils are fried,
the same for locomotives... easy pickings as soon as the enraged and
frustrated locals kill each other off or just starve under bushes.

so just why in hell would you WANT to drop one to several thousand feet
above ground level and try to pulverize stuff and poison the ground?
you can't use anything then, and the fallout would be brutal world-wide.

Ed Price wrote:

"Dick Carroll;" wrote in message
...


Chuck Harris wrote:

Hi Dick,

EMP testing was done in the open air blasts in the Marshal Islands.
EMP testing was done under the desert in the Nevada tests.
EMP testing was done above ground in the US Army's facilities.

It is very well understood.

I wasn't clear. One's proximity to the event will mean everything, that's
the uncertainty,
along with the device yield.
. Close enough and you will certainly have problems. No one will know how
far away you have to
be to avoid them.


Both ground and air nuclear burst will cause an EMP. Further, the power will
fall off at 1/r^^2, but the field strength decays at 1/r. Devices may fail
due to induced power or voltage (for instance, a high impedance FET gate
might easily fail with only a very modest induced voltage).

The air burst NEMP can be optimized by placing the detonation just at the
outer fringe of the Earth's atmosphere. The device is designed to direct an
intense x-ray burst downward into the atmosphere. This energy interacts with
the Earth's magnetic field, causing an intense EM field to propagate toward
the Earth's surface. Since the optimum burst height is defined by the
density of the atmosphere, there's not much you can do to increase your
separation distance (short of digging a very deep hole).

Back in the good old days of the USA / USSR cold war, when both sides had
plenty of nukes, any serious exchange of weapons would have made diverting a
few to NEMP optimization a cheap investment (considering the potential for
disruption).

Ed
WB6WSN

-- If it's a "new economy," why do they want my obsolete old money?