Simplex Operations and Equipment
Antennas
The importance of increasing antenna height cannot be stressed highly enough.
A 4-element Yagi elevated 15 ft. with 25w from an HT+brick amp out performs 100 watts into a typical mobile whip mounted on the car trunk lid. If you don't use a portable mast, at least drive to a high spot away from power lines to operate. Using a portable mast mounted base antenna or Yagi enables you to use less power to save your batteries. Some of our operators use a ground radial adapter, which enables a mobile antenna to be attached with hose clamps and elevated on a portable mast. The rest use a small dual-band base antenna with at least 3db gain.
Antenna Recommendations
Cushcraft's AR-270 dualbander is only 3.75 feet high. 5/8 wave on 2m and collinear on 440. The Diamond X-SON is another compact dual-band antenna which fits into an SUV. Their performance and VSWR are also acceptable for low power 220. Both are ideal either for portable use or attic installation where there are restrictions on outside antennas.
Most mobile VHF operators use 5/8 wave 2-meter whips.
These will also work as a 1/4 wave whips on 6 meters if you feed both rigs through a diplexer. If you use a dual-band radio the Larsen NMO-2/70 is hard to beat. Serious 2-meter mobile simplex operators like the Diamond SG7900, Hustler CG144 or the Lakeview 2m hamstick.
Bicycle / motorcycle / marine mobiles, fiberglass van or ambulance bodies without a ground plane require half wave antennas (Diamond SG7200 or Comet CX-224) which provide unity gain without a vehicle ground.
Sometimes you have to be creative in mounting an antenna to non-metal vehicles. The Radio Shack window-clip mount enables attaching a BNC whip to your HT while having a clear RF path outside the vehicle.
For simplex operation from fringe areas, small yagis such as Cushcraft's A148-3S or 124WB are compact, have good gain and a wide useable pattern.
Short Yagi antennas of about 1/2 wavelength with up to five elements can be used in fixed position without the frequent re-aiming required of long "boomers." Color-code elements, use wing nuts to ease reassembly and store the antenna in capped PVC pipe.
We do not recommend for EmCom the use of mag-mounts constructed using RG-S8 coax having a solid center conductor.
This cable is suitable only for permanent vehicle installations where it will not be subjected to repeated flexing.
Factory installed crimp-UHF connection on mag-mounts should be reinforced behind the reducer with heat shrink or tape.
Frequent flexing eventually causes failure of the shield at the connector, at the worst possible time.
Good simplex performance results from using an efficient antenna, elevated as high as you safely can above surrounding ground elevation, using the shortest run of low loss feed line, providing the highest effective radiated power for the least battery consumption.
A unity gain, quarter wave mag-mount thrown on top of the nearest metal object may work fine for local repeaters, but on simplex will be lacking, unless you have height and a "straight shot."
Use RG8-X only for HF runs less than 100 ft, jumpers and short VHF runs to 30 feet and for mobile installs.
Use RG-8 or RG-213 for HF or 6 meters for runs up to 200 ft. or 2 meters up to 50 ft. Use LMR400 for VHF runs over 50 feet and all uses above 200 MHz.