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Equipment / Re: The best undercover fm antenna on the market. DIY 1/4-wave!
« on: January 29, 2018, 0434 UTC »
That dude that wanted to build 1/4-wave GND Plane planes. Ya really wanna' see how I do it? (For RX'ing purposes, right? Hi-hi...) Here's one (Of many.), site(s) to show how to build a 1/4-wave Ground Plane. http://www.localmeridian.com/2016/06/build-your-own-antenna-14-wave-vhf-ground-plane-antenna/ I, however, find my GND Radials and Vertical Radiator lengths a bit differently using speed of light (In Meters per second, 300,000,000.), over frequency (In MHz.). The four GND Radials are calculated 1st. BTW, they can be any metallic material. Copper and brass are solderable, while I've seen steel welded. Let's use the FREQ 98.1MHz, for example. Let's drop 6 decimal places and do 300 / 98.100 = 3.058 Meters for full wave length. We want 1/4-wave, so divide by 4 = .765M, or 76.5cm. For standard size, .765 X 39.4 = 30.122, or 30 1/8". So, each GND Radial is going to be 30 1/8 inches in length. (As seen in that preceding website, fashion into 45 degree. Now, for the Vertical Radiator, I use #10 AWG solid copper bare wire. Why??? Cause, I've had very good luck with it, and I can't afford to make it out of the next best conductor, silver. We know that each 45 degree GND Radials will be 30 1/8" for the FREQ of 98.1MHz. If we were in outer space (A vacuum.), then we could make the Vertical Radiator that length, but to really fine-tweak out VSWR match to 1:1.1 (As possible.), I compensate for being at sea level with an atmospheric pressure of 14.7psi. How? Deduct -5% of length. So, 30.122 - 5% = 28.616, or 28 5/8 inches (Close enough.). And, what coax can be used? Mini 8 (RG-8X), works well since it's less lossy than the 2M HAM 144MHz FREQ's and especially VHF-High TV FREQ's. And, it's affordable. I do suggest using using teflon PL-259 and SO-239 connectors. Do no weather proofing directly on RF solder points with silicon caulk, or tapes, as they effect the RF skin conductivity. Heat shrinks and cured Liquid Tape actually works well here. Get it? Got it? GOOD!!! Now, start building!
