"Larry W4CSC" wrote in message
...
On Sat, 8 Nov 2003 20:09:43 +0100, "Meindert Sprang"
wrote:
You just take every opportunity for a rant about NMEA, don't you?

What rant? The truth is an unshielded RS-232 serial connection with
ground hooked to one side of the damned balanced line is a big
transmitter! Unshielded plastic crap has no business around an HF
receiver with any kind of a switching IC inside it.
Well....duhhhh....

That is nonsense. It all depends on proper PCB design. I HAVE measured it,
for crying out loud!

Why would NMEA at 4800 baud produce more interference than a 100mbit
network
on UTP (U=Unshielded)?

Well, duhhh.....Lemme see....we have a 4800Hz square wave...so
starting at the fundamental frequency of 4.8Khz, a square wave (just
pretend it's not data for a minute) has an odd harmonic every 4.8Khz
from 4.8Khz to....well....30 Mhz, easy?

You were talking about interference on 2400MHz, right? Apart from that, have
you ever heard of slew rate? A properly filtered 4800 baud output has
filters on it, which just cuts off any higher harmonics that can be
dangerous. So even with a single wire hooked up to the NMEA output, it can
be silent on HF.

Hmm...100mbit is 100 Mhz. So, there's a carrier buzz around the upper
end of the FM band....then there's that 3rd harmonic at 300 Mhz, way
above Channel 16, as it were....well? Duhh....

Of course, the wireless network equipment is all built to FCC
SPECIFICATIONS (i.e. Type Accepted, Class B Computing Device?) and is
SHIELDED to pass?.....well, duhhhh... 2400 Mhz isn't gonna tear up
anything on our boat. Will it yours?

Nope.

NONE of the plastic boxes the damned cheap marine crap comes in is
shielded in the first
place against the HF transmitter or your 5W walkie talkie on deck.

Yes. Tried it. 15Watts of VHF against the box didn't hurt it. We tested up
to 12V/m (that is above the required limits of IEC945) and it kept on
working.

May we test your plastic box in the FCC Lab? I can make that
arrangement if you like.....

Please be my guest.

Meindert