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Author Topic: Radials on raised vertical  (Read 683 times)

Posts: 37

« on: December 11, 2009, 02:39:51 PM »

This may be a dumb question but I plan on getting a new vertical for HF. My pole is 20 feet high about 3 feet above the roof line. How do I attach radials to the antenna? Do they lie down on the roof? The pole is secured by a clamp to the roof eave.

Posts: 59

« Reply #1 on: December 11, 2009, 03:15:36 PM »

why on 20' pole asking for trouble

Posts: 60

« Reply #2 on: December 11, 2009, 04:05:32 PM »

A couple of suggestions - I assume that your vertical requires 1/4 wave radials. If the 3 ft. pole above the roof can not accommodate the stress from the vertical in windy conditions, fan the radials from the top of that pole (at the base of antenna) as guy wires.   Cut the wires to 1/4 wavelength.  You can also fan the wires from the base of that 3 ft pole along the roof surface but subtract the 3 ft from the radial 1/4 wave lengths.  I have done so in the past with excellent results.  If the base is 20m feet above ground, you should get acceptable results on 20 through 10 meters with 3 or 4 radials per band. Don't expect great results on the lower bands unless you have more radials but even 4 should allow adequate performance.  Raising the vertical to roof level mitigates problems with surrounding RF obstacles (buildings, etc) so you're on the right track.  There are lots of articles about vertical counterpoises - if you want more details, conduct some web searches but bottom line is that the more radials you have, the better your TX performance will be.

Posts: 7718

« Reply #3 on: December 12, 2009, 10:27:26 AM »

Two resonant radials per band will do the job and result in little radiation from the radials. If you have room for only one radial on a band that will work. The radial will radiate as well as the vertical. You will make contacts.

How you dress the radials is not too critical. I would not run them close to the metal flashing at the edge of the roof or close to metal gutters.

A 1:1 balun can be added if you would like to reduce coaxial cable shield current (and radiation). The shunt impedance provided by the radial(s) substantially reduce feedline shield current.

Posts: 10248


« Reply #4 on: December 12, 2009, 10:38:26 AM »

When it comes to radials, elevated or not, here is the standard:

Alan, KØBG


Posts: 1454

« Reply #5 on: December 13, 2009, 02:00:57 AM »

Having actually built verticle antennas I can tell you that if it were me, I would use at least four 1/4 wave radials connected to the grounded section of the antenna base for best performance. An easy way to do this is to use a large hose clamp and 1/2" copper pipe clamps with pre drilled holes. Use stainless steel bolts, nuts and split washers to attach 14 AWG copper wire to the grounded assembly. I always crimp and solder weatherproof connector rings to both ends of the radial wires to make installation easy and strong.  

The radials can be part of a guy wire system for the antenna as long as they are insulated at the ends from the rest of the guy wire system. I use nylon cord for this and it works great. This method also serves to elevate and angle the radials correctly.

You can add electrical conductive material to the bolt assemblies and wire to ensure a good weather resistant connection. Another good weather resistant trick, after assembly, is to spray paint the antenna flat black with $.99 spray paint. It also helps hide the antenna from grousing neighbors. I paint all of mine.

Posts: 2276

« Reply #6 on: December 13, 2009, 09:43:24 AM »

I made one and it works very well. It is a hill top dx antenna that I mounted above the roof top of the mobile. Goto my eham call search and look at the large photo, scroll around to see it close up. This design is sound notice that I utilized a non conductive pole but the radials will de couple a conductive pole too. I had the wooden closet pole handy so I used it. I call it a ground plane but really we should veiw it as a center fed vertical dipole where one half is the aluminum pole and the second half is the 4 radials split symmetrically around the semi circle and sloped in this case at roughly 30 degrees and secured tightly with non conductive tent stakes. The concept lends itself nicely to roof top installs or pole sections and phillystrand guy rope dacron etc. The base height where we feed one goemetric center etc need not be high for single lobe developement. Mine matched properly, one could tune this antenna by either adjusting the pole of nested tubes or by folding back the radials some. keep the slope angle of the radials equal, keep the radial lengths equal, and set them at equal distance around the semi circle. EG 0 -degrees,90- degrees,180 -degrees and 270 -degrees around the compass. Great dx antenna on 20m. The design is reasonably repeatable anywhere. Open pasteur is optimal but I would not hestitate to roll into any area and use this center fed vertical dipole/ground plane.
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