> Joshua M. Arritt jarritt at vt.edu
Wed Mar 2 11:02:46 EST 2016 wrote:
>
Galvanized Fe material is problematic from an R standpoint as well (vs.
Cu). This results in a "lossy" ground plane. That condition has real
impact the effectiveness of the antenna system, when compared to an
all-Cu (or at least a lower-R metal) plane.
>
I'd think that kind of loss would be minimal, and should be the least of
worries. What about AM broadcast towers, nearly all of which are built out of
galvanised steel, or in some cases ungalvanised steel, merely painted to retard
rust and to meet FAA requirements? I recall a story about an AM BC station in
Puerto Rico turning to galvanised barbed fencing wire for radials, after their
copper wire system had been destroyed for the second or third time by copper
thieves, and the FCC did not hesitate to give them the OK. I also remember
seeing an AM BC tower under construction in Ethiopia back in the late 60s using
steel fence wire for radials. The climate there is so dry that the steel wire
would probably last more years than pure copper does in moist, acidic soil as
we commonly have in New England and elsewhere. The obvious reason steel was
used there was to cut costs.
> Immediately perceived consequence of the poor inter-section bonds is
walking VSWR, but other factors (including rad efficiency) are also
walking around.
>
That might be problematic, but measures could be taken to make sure the pieces
are well bonded electrically. If the sheets are securely bolted together, that
might be sufficient in itself. Again, galvanised steel tower sections like
Rohn 45G are used as AM BC towers merely bolted together; I have never heard
any mention of a necessity to further bond them electrically. The zinc coating
with real hot-dipped galvanising makes pretty good electrical contact between
sections, provided they are securely fastened.
> Bonding of dissimilar metals (Cu <-> Fe) requires careful method
> consideration to hold corrosion at bay.
Direct contact between copper and zinc must be avoided at all costs, since
those two metals are highly reactive with each other and corrode at the first
contact with moisture, producing a diode rectifier at every joint or
connection. OTOH, brass is OK. It is often used as a go-between for bonding
zinc with copper, for example, ground clamps used to attach a copper wire to a
galvanised steel ground rod.
Don k4kyv
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