Re: AMOS antenna messing ***

On Oct 18, 8:42 pm, Jeff Liebermann <je...@xxxxxxxxxx> wrote:
On Sat, 18 Oct 2008 14:41:31 -0700 (PDT), m...@xxxxxxxxx wrote:
On Oct 17, 11:50 pm, Jeff Liebermann <je...@xxxxxxxxxx> wrote:
On Fri, 17 Oct 2008 13:13:10 -0700 (PDT), m...@xxxxxxxxx wrote:
So are you OK with copper flashing for the reflector?

Sure, but copper is expensive overkill.  I suggest aluminum with a
brass grommet for soldering to the coax braid.
Looking back at the article, it seems the ground plane floats, so you
don't need to connect it to the coax braid. Or did I miss something.

It can either float or be grounded.  I've seen it built both ways.  I
haven't tried tweaking the model to be sure, but my astute guess is
that it doesn't matter because the balun eliminates all radiation from
the coax shield.  For example:
<http://pe2er.nl/wifisector/WifiSectorAntenneFeed.jpg>
shows that it's grounded.  That's also the way I like to do it because
of the added mechanical rigidity.

If I need to connect to the ground plane, then copper is probably the
way to go.

I can see you've never tried to solder to a giant copper heat sink.  I
had to use a propane torch with a huge copper soldering tip in order
to generate enough heat to solder to copper ***.  Worse, I was
soldering the copper directly to the coax braid.  By the time I got it
hot enough to melt solder, there was enough heat saved in the copper
to melt the dielectric.  The nice thing about the rivet trick is that
the thermal connection between the brass rivet and the aluminum heat
sink is minimal.  Therefore, the heat stays in the brass rivet and it
solders easily.

Otherwise the connection corrodes. I've built antennas out
of Al and used the dielectric goop from the hardware store, which
works for a while, but ultimately the connection goes bad.

Hints for aluminum (from experience with designing marine radios for
about 9 years).
1.  Don't use stainless and aluminum.  Use ugly hot dipped galvanized
screws.  Those are the dull gray colored screws, not the shiney ones.
2.  Wash the aluminum in vinegar before painting.
3.  Forget about dielectric goop, contact cleaner, silicon grease, and
other crap in the connector.  Mate the connectors dry and do whatever
is necessary to waterproof the connector.  I mummify the connectors in
PTFE tape followed by a layer of Scotch 66 electrical tape.  I
recently disassembled a connector pair that's been on a tower near the
ocean for about 8 years.  The connector guts were perfect, but the
crappy copper plated clamps rotted through the jacket and trashed the
coax.
4.  Copper corrodes into copper oxide, sulphate, sulphite, etc all of
which are lousy RF conductors.  The elegant copper patina is useless
for RF.  If you must use copper outdoors, invest in a silver plating
bath and plate it.  The sliver will turn dark (silver sulphate) but
conducts RF even better than shinny silver.

--
Jeff Liebermann     je...@xxxxxxxxxx
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Well, if I can float the ground, I'll go Al foil on plastic. I will
first see what the Al Rem Center in Santa Clara charges to cut some Al
plate to size. Or I may get lucky and find some Al the right width and
longer than needed, then just hacksaw the along the short direction. I
don't know if you ever bought metal there, but these guys are busy. I
think the walk in sales are a minimal part of the business.

I have soldered to copper plate, and it is a PITA, though not
impossible. I built one of those biquad wifi antennas. I tinned the
copper first. When soldering the N female jack to the copper, I put a
sacrificial N male plug into the jack. This kept the center pin from
moving around.
.

Loading