A long Yagi antenna is the very best T-Hunt antenna for stationary use. This is because it has a large aperture without having to be moving. Thus it can provide a very good indication of the direction of the strongest path, and probably several weaker paths (provided they are not too close together in direction).
What is the best large beam antenna for fixed use? I believe it is two medium sized (minimum of 6 elements each) Yagis stacked horizontally. There is a formula for staking horizontally to obtain the minimum side lobes (look in the ARRL Handbook). It is a function of the gain of the two (identical) Yagis to be stacked. Minimum side lobes is important, because it means that a response from a weaker path is easier to separate from the antenna's side lobe responses. (Note: maximum gain does not occur with minimum side lobes.)
Very long Yagis present mechanical problems for mounting on a car. They have a lot of mass that can put stress on the mounting. They must be stowed in a fixed position while moving. It is doable. One hunter here had 11 elements on a mast up through the center of the roof on his van.
Another problem with hunting with the beam is that you must pull off the road and stop to take a bearing. While moving, there can be too much multipath fluctuation of signal strength to be able to peak a reading accurately. Having to stop to take readings can be a real problems in hunts where the signal is intermittent. It "never" comes on the air when there is a place to pull off the road, and it "always" does when there is no place to stop! (At least it seems that way!)
Small beams make good mobile T-Hunt antennas. Mounting is not too difficult. They provide some gain for when the signal is weak. They rotate quickly with just a flip of the wrist.
There are some designs that are better than others. The 3 or 4 element quad is a favorite here. The really important thing is minimum side lobes. In the dynamic excitement of a T-Hunt, this is more important than gain. While a small beam will have difficulty sorting out weak paths, the minimum side lobes means that with one quick spin of the antenna, it is easy to spot when the front lobe passes over the signal; there will be one big jump in the S meter. I have such a beam, made by my good friend Ray Frost, WA6TEY (now a silent key). It has only one lobe. I hope to publish the design on this page.
The best T-Hunt antenna for stationary use.
Can measure the angle of elevation of the signal when used hand held. Can hunt either vertical or horizontal signals (by changing the mounting). Fairly good sensitivity.
Its major weaknesses are that it requires an S meter and an attenuator in order to hunt. Even then, many setups cannot hunt in close to a reasonably powered signal, such as another mobile. The problem is that there is enough signal leaking into the radio by paths other than the antenna to drive the S meter to full scale. The system is then completely useless. Not accurate if used in motion. Frequency coverage of only a few MHz.
George Russ Andrews
President
George R. Andrews (Russ, K6BMG)
BMG Engineering, Inc.
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(7 Feb 1996)
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