RevGary
Pastor and Chaplain Responder
- Joined
- Oct 22, 2005
- Messages
- 806
There are some used Cushcraft A147-11's available on eBay for persons with VHF high band scanners. These antennas were designed for Amateur 2 Meter operation but can be quickly converted to center band operation at 155 Mhz with these modifications:
Leave all element spacing as it is. For scanning only, the spacing does not have to be changed. However, shorten all elements by using a tubing cutter and take off 1 inch from EACH END on all 11 elements. MAKE SURE that the driven element is exactly 35 4/5 inches in total length. The tuning bridge also needs attention... loosen the sliding clamp and pull the stub out by 1/2 inch from the heat shrink tubing and re-tape it in that location. Slide the clamp toward the boom on both the stub and driven element by 1/2 inch and secure it in place. This brings the resonance of the beam up to 155 mhz from it's original 147 mhz mid band resonance. After completeing these mods, all you need is a medium duty rotator for a marked increase in VHF high band monitoring. we are now able to monitor agencies 215 miles away regardless of atmospheric 'help'. Forward Gain, dBd: 13.2, Front To Back Ratio: 20 DB, Boom Length: 12 Feet, Weight: 6 LBS - not much wind loading on this antenna. Thanks to customer service at Cushcraft for providing the measurements and advice.
Leave all element spacing as it is. For scanning only, the spacing does not have to be changed. However, shorten all elements by using a tubing cutter and take off 1 inch from EACH END on all 11 elements. MAKE SURE that the driven element is exactly 35 4/5 inches in total length. The tuning bridge also needs attention... loosen the sliding clamp and pull the stub out by 1/2 inch from the heat shrink tubing and re-tape it in that location. Slide the clamp toward the boom on both the stub and driven element by 1/2 inch and secure it in place. This brings the resonance of the beam up to 155 mhz from it's original 147 mhz mid band resonance. After completeing these mods, all you need is a medium duty rotator for a marked increase in VHF high band monitoring. we are now able to monitor agencies 215 miles away regardless of atmospheric 'help'. Forward Gain, dBd: 13.2, Front To Back Ratio: 20 DB, Boom Length: 12 Feet, Weight: 6 LBS - not much wind loading on this antenna. Thanks to customer service at Cushcraft for providing the measurements and advice.
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