Interesting topic.
My experience was with a triband spider quad many years ago.
Had the quad up for about three years in a relatively mellow climate (no ice
etc).
The solid conductor wires and the cane spreaders gave no trouble at all.
Copies of this quad can be heard from ZM1A contest station.
Am no metallurgist.
At the time I got advice from a warehouse specialising in non ferrous
metals.
This from memory and an aging brain:
Copper conductor comes in two varieties, soft and hard drawn.
Soft is, well, soft. It work hardens ie if you bend it or beat it for a
while it goes hard.
Where it goes hard it goes brittle.
You can soften it again by annealing it, ie heating it up and letting it
cool.
Hence you can have problems with copper wire, most likely where there are
bands eg corners of a quad element.
There are many alloys of copper. The folks at the warehouse sold me, as I
recall, phosphor bronze wire ,which is springier and less likely to fail
than pure copper.
Need to radius a bit at the bends.
I used single conductor about 14g.
Using bare conductor has one advantage: If you can get at the bottom of the
reflector elements to tune them, then the conductor ends can be overlapped ,
fixed with a small brass cable clamp and adjusted for length.
There is a sweet spot at a certain frequency where the quad pattern has a
narrow deep null at the back.
Just point the back of the quad at a signal source and adjust the reflector
while listening to the sig with an extension speaker. The null is so deep it
is obvious without metering.
With insulated wire one would have to trim with great care that one did not
overshoot. Maybe go for the null at a slightly lower than optimum frequency
so you cna get it right. Assuming sensible insualtion in the region of the
spreaders, the choice of wire insulation should be on abilty to sustain
weathering rather than electrical properties. BTW, running the elements
through short lengths of PVC tube where they cross the spreaders gives some
insulation and gives some radius to the bend, important to avoid mechanical
failure at this point.
I once bought at sale price some reels of tinned 7 stranded iPVC insulated
hookup wire, maybe 2mm o.d. Over the years have used this for all sorts of
wire antennas by spinning two lengths together with a drill. This wire is
light, strong and quite tough. Also flexible. Have never had it fail from
flexing. Would imagine it would have quite a substantial rf diameter, too.
Have not used it in a quad, but could be OK.
73
Barry ZL1DD
PS At ZM1A we went over to the quads because A-B comparison on receive
showed them significantly better than one of the best commercial triband
beams. Not wanting to restart an old fight, but that is how it was for us.
--
Barry Kirkwood ZL1DD
barrykirkwood@gmail.com
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|