Everyone is searching for the holy grail of Part 15 AM transmitter installations. It's all very simple. A base-loaded vertical is the time honored and proven best antenna. Stop fretting about top-hats, center-loading, etc. They don't help much and are either legally questionable or physically impractical. Prior to the (redacted - let's not discuss people who aren't participating) era, the easiest way to dramatically increase your range was to elevate your transmitter/antenna to 20ft or 30ft or more. Now, we can only fall back on stretching other parameters to compensate for the loss of height. Ground Radials: antenna modeling software shows a dramatic improvement in field strength for a ground-mounted 3m antenna when you install 32 to 64 ground radials at least 30 ft long (ouch, pain, chiropractor...) Loading Coil Efficiency: when the antenna radiation resistance is only .1 ohm, the MAJOR loss is in the loading coil. Typical "good" coils have a series resistance of about 15 ohms. This "huge" resistance is the overriding factor in determining overall loss. Any incremental improvements of the antenna (like a top-hat) will only increase the radiation resistance by another .1 ohm or so. The holy grail here is to find a way to reduce the loading coil resistance. A big air-core coil is the best possible. It can cut the coil loss to as little as 5 to 10 ohms. (again... ouch, pain, maybe not a chiropractor). It seems to me that the masses are always brainstorming oddball antenna alternatives rather than focusing on the real agenda. The brainpower of the masses would be much better spent on how to reduce the losses of the loading coil. That's not as much fun as imagining the result of using an upside-down mailbox as the ultimate antenna, but it is reality, not fantasy.
March 12, 2011 - 06:10#1
Ultimate Part 15 AM Installation