FWIW, I used 60 number 16 bare solid 1/4-wave radials on each element of my
40M 4-square, pinned to the surface with bobby pins and bonded in the center
square at the overlap points (possibly not necessary but I did it anyway.)
They're slowly burying themselves. The array works great.
I chose number 16 for mechanical strength. I have heard that wire gauge is
not important from an RF perspective, but it certainly can be important from
a mechanical perspective. I would be a bit concerned that number 28 bare
wire might not stand up to the mechanical stresses over time, particularly
if the attachment point at each element is on the surface.
As far as I know, there is no RF advantage to insulated wires. I suppose the
insulation might retard corrosion of the wire, but that may not be terribly
important for buried radials, where oxidation would probably be slow. As for
stranded vs solid, perhaps the wire with lower inductance at the design
frequency would be preferred, but I have a hard time believing that the
difference between solid and stranded wire of the same gauge would be
meaningful in this context.
> The system was carefully tuned using a 4 channel 100mhz scope with equal
> length sampling lines and small current xfmrs at each tower.
This sounds interesting, but I'm not familiar with the method. Can you
provide us with more details about exactly how you used the scope to tune
> The system
> worked well and was good for 39 zones worked. HOWEVER, a local friend
> with a 4 Hytower array using small insulated hookup wire radials always
> matched my reports and now and then beat mine.
Did his system have the same number of radials as yours? From what I've
read, 20 radials is a pretty marginal number for a ground-mounted system,
and that you really need to have 60-120 to overcome ground losses, even if
the soil conductivity is good (the rate of improvement begins to diminish
after 60, and pretty much dissapear after 120.) A smaller number of radials
might be OK if the antenna is surrounded by a salt marsh. I suspect that the
effect of too few radials would be to exaggerate any local differences in
soil conductivity between your location and his, and that this might be the
explanation for the differences in signal reports ("location, location,
location...".) My advice is to install at least 60 radials per element and
120 if you can, using any wire that can stand up to the mechanical stresses.
Tom Rauch, W8JI, has made extensive measurements of ground systems for
vertical arrays. You might want to drop him a line at firstname.lastname@example.org
73, Dick, WC1M
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Administrative requests: towertalk-REQUEST@contesting.com