I had been using a Diamond X510 antenna mounted to a six foot pole attached to my deck (10 feet above ground) and had pretty good luck with 2m and 70cm repeaters. However, when I used it as an antenna for my scanner, decoding about 60% of the packets on the statewide trunking system. So I replaced the Diamond X510 with a Comet DS-150S Discone antenna.
My initial tests were done using a 9 foot mast in the same location. While the 2m and 70cm machines appeared to be about the same signal strength, the 850 MHz trunking system was substantially lower than before and the decode rate had dropped from 60% down to 40% — odd given that the discone is wide-band. I also checked the SWR on 50.1 MHz and found it to be about 4.5:1 and much worse at higher frequencies.
On a whim I swapped out the 9 foot mast for a 12 foot mast. This brought the 850 MHz trunking system up to full strength and 100% decode — much better than it had been when using the X510. Pleasantly, the SWR on the 6 meter band became more manageable with an SWR of 2.4:1 at 50.1 MHz and 1.2:1 at 52.0 MHz.
What a difference 3 feet can make!
