Compensator Capacitor

Figure 4. Two methods of feeding

A third, more complex, solution is to mount a remotely-con-troiled coax switch at the antenna and use that to switch between bands. Whatever the method of feeding, it's best to avoid long runs (over 50 feet) of RG-58 at these frequencies due to its relatively high fosses. Use RG-8 or -213 if at ail possible.

The quad performs best when to obtain horizontal polarization.

the bottom of the quad is one-half wavelength or higher above ground. When mounted closer than this to the ground, radiation is reduced at the low angies commonly needed for iong distance communication at 28 MHz.

Tuning the Spider

The final step is to tune the

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Figure 3, Spider quad dimensions.

antenna for maximum performance, It's possible to use the antenna "as is," but tuning the reflector stub yields optimum performance. The reflector may be tuned either for maximum gain or for best front-to-back ratio (the latter is normafly done).

Aim the back of the antenna at a nearby (but no closer than a few hundred feet) signaf source and adjust the shorting bar for minimum signal, if using the gamma match feed system, it s necessary to appiy a low fevel of power to the antenna and adjust the match for minimum SWR. If it is a multiband quad

Figure 5, Details of gamma match for multiband design. Once adjusted. the variable capacitors may be replaced with fixed mica capacitors of the same valuel See text for adjustment details. Each band must be adjusted separately with great care.

with the gamma matches connected in parallel, adjustment for minimum SWR is more involved. With that system, the taps and associated variable capacitors of the gamma matches need adjusting for minimum SWR on each band. Adjust the compensator capacitor if necessary to improve the match. By repeating those steps several times ft should be possible to get a low SWR on each of the bands.

That's all there is to it. This antenna is easy to build and a good performer. Try it out as the new sunspot cycle breathes lite into the higher frequency HF bands.10

Figure 4. Two methods of feeding

A third, more complex, solution is to mount a remotely-con-troiled coax switch at the antenna and use that to switch between bands. Whatever the method of feeding, it's best to avoid long runs (over 50 feet) of RG-58 at these frequencies due to its relatively high fosses. Use RG-8 or -213 if at ail possible.

The quad performs best when feed

PO'INT

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