Mission Viejo Special, The Multiband Vertical (#4 of 6)

Radial Plate

Feed Point / Radial Plate

Radial Plate

Defining a good feed point, and grounding base in particular, is mighty important for a construction of a vertical antenna. Any spurious resistance or reactance can become a significant power drain. No one wants that.

I saw the radial plate from DX Engineering and a few other places. They are nice. They are also too expensive, in my book. So I went to the Industrial Metal in Irvine and had an aluminum plate cut to a size and drill / bend them at home to make one myself. $20 bought me a 3 or 4 proper sized plates for the purpose.
The size of the plate is not critical. It just needs to be big enough to accommodate eight (or more) holes to attach counterpoise wires, in a circular fashion centered with an SO-259 coax receptacle.
¼” self-tapping bolts are used to attach the counterpoise wire with terminal lugs attached.
The plate is bent in an “L” shape with holes to put a pair of 52mm U-bolts for the attachment to the bottom of the fiber pole mast.
After the feed wire to the radiation element is attached to the SO-259 connector, it should be wrapped tight with the silicon sealing tape for weather proofing.


Top Boom

Feeed Point

Horizontal Booms: Wire Support / Feed Point

I attached a pair of horizontal bars, at about ¼ from the top and at the bottom, to keep 20m and 30m wire elements parallel and separate from the mast, preventing the three wire elements from shorting each other. As it is, the wires are about 15cm from the mast. In afterthought, that could have been a little wider.
I had a stock of 25mm (OK, 1”) PVC pipe to use as a horizontal support bars. You can get them at Home Depot. I also needed a U-bolt with mast clamp, which proved to be harder to find. The area Home Depot didn’t carry those since most HOA around here prohibits the TV antenna, there is no market for them. You can find them at DX Engineering, but they are a bit pricey. You will need one for 32mm (1 ¼”) and 52mm (2”) mast bracket assemblies. I found one for 32mm at hardware stores outside of the region (like Anaheim, at ORVAC). But you may not have much choice for 52mm outside of DX Engineering, or some other web-order stores. I happned to have parts from old trap vertical antenna. You will also need two more 52mm for the radial plate, though just a simple U-bolt without the mast bracket might suffice for that (yes, you can find them at local Home Depot).
The support bars are just 25mm PVC cut to about 40cm length, then drill holes for U-bolt bracket and the antenna wire. The bottom bar, the same length, also serve as the short bar, to connect three element wires to serve as the feed point. I wrapped a sheet of cupper foil (purchased at HRO some time ago) over the drilled PVC.

Top and Bottom Booms

Top Section sketch

Ü Introduction Þ
Mast, Base Radial Plate Boom Elements
Grounding UNUN Tuner Adjustment
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