Batboard

i finally found some decent aluminum to make the ground planes for my station master...

i assume that there are three ground planes required... anyone know the length (1/4 wave?)

doug

I don't know if the length is that critical (at least 1/4w+10%) as much as the angle at which they are installed.

typical designs are 1/4 wave radials, drooped about 45ish degrees will give you a better pattern out on the horizon.

If it were me, id put four radials on it, if possible.

If the radials are at a right angle to the antenna then you probably will not have a 50 ohm resistive match. If you bend the radials downward you'll reach a point where you have a 50-ohm match.

However, I've observed that gain verticals always have really short radials, and I don't understand the theory which governs this.

You might also be able to get the data you need from a website of the manufacturer on a Google search.

You can buy a brand new and complete OEM ground plane kit from the manufacturer (now RFS, used to be Cellwave) for next to nothing. Why fight it?

Larry

My two bits worth:
I am under the impression that this is a stacked co-linear antenna, and the "radials" are intended to de-couple the antenna from the supporting structure.
Most useful for increasing isolation of antennas on a tower.
If this is to be an antenna solo on a roof or tower I don't think that it makes much difference wether they are there or not.

this antenna is now in service on a highly populated cell site doing just fine.

i see about 1w reflected pwr at 75w forward...

so i am going to leave it alone for a looooong time.


doug

For comparison, I have a stock, two-year-old super station-master antenna on my repeater, built for 440-450 MHz, transmitting on 444.450. It's side-mounted (maybe 5 feet off the tower), is connected with 6 feet of Cellwave 1/2 inch SuperFlex coax, has an anti-sway support holding the top, is mounted about 400 feet up on a 600 foot tall tower, and is being fed with about 550 feet of Cellwave's 7/8 hardline. I'm using N connectors throughout. With a Bird 43 wattmeter and CDI elements at the repeater end of the coax, the last readings I took showed 68 watts forward on a 100w element, and about 1/2 of the first minor division on a 5w element for reflected power. That would be less than 1/10 watt, if you can even trust the meter to be at all accurate down there. It's barely enough to move the meter pointer, but it does move.

I wasn't around when the antenna was installed, so I don't know how well it was assembled by the tower crew, but I'll accept those readings any time ! I agree with your intent to leave yours alone !

Bob M.

The true Station Masters, the earlier ones have three straight 1/4 wave radials aprox. 1/2" below the top of the alumimum support housing. The later ones use three 1/4 radials, but at a -45 degree angle, flat side to the support tube held by a radiator hose clamp.

Made by Phelps Dodge, then Cellwave, now Radio Frequency Systems.

DB Products makes a simmular looking fiberglass antenna that does not have any radials.