Like Mike, I also have the MFJ-1800. And boy was I
surprised when none of my shack full of type N to SMA
adapters didn't work. I can't believe they reversed the
polarity of the center pins for WIFI SMA connectors.
Urrrrgh

That's due to an FCC requirement. The FCC says (or used to say) that
the antennas on consumer-type Part 15 wireless gear had to be "not
commonly available" or words to that effect. Reverse-polarity
gendering, reversed threads, etc. are all common techniques... and of
course, as soon as one is used, it rapidly becomes so popular that it
ceases to be "not commonly available" :-)

The specific intent was to try to discourage consumers from changing
the antennas on WiFi gear. The certification of WiFi equipment is
done on the system as a whole (radio + antenna), and changing to a
higher-gain antenna automatically invalidates the certification and
makes the WiFi system technically illegal to operate (at least, until
it's re-tested and re-certificated with the new antenna).

If I recall correctly, the FCC modified the rules a year or two ago.
A system's manufacturer is now allowed to test their system with one
or more types of antennas, having different amounts of gain, and
publish the gain number for the highest-gain antenna with which the
system has been successfully certificated. It's then legal for an
installer to substitute a different antenna than the original... as
long as the substituted antenna has the same, or lower gain than the
highest-gain antenna that the manufacturer has certificated.

These rules are, I suspect, honored far more in the breach than in the
observance... and there seem to be very few manufacturers who go to
the trouble of publicizing the "highest-gain antenna allowed with this
system" information. That's probably going to be done only for
high-grade commercial gear, not consumer-grade routers or the like.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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