A short circuit at DC works quite differently than it does at RF. Consider it a strategically placed needle in the coax. The 'needle' is on another sort of side line to the coax. You use a Tee connector. Radio to one, antenna to another, and the 6-foot shorted line to the third. It gets installed permanently in the line, and can be in place for transmit or receive.
Depending on the source of noise it may assist. Anything that is being generated at 27MHz will not be stopped. However, if it is a static discharge problem within the antenna itself, the antenna will now be fully DC grounded and any static discharged. It won't do anything for reducing noise coming from a pole transformer, vacuum cleaner, etc. Transmission line - Wikipedia, the free encyclopedia
Zin = Zo^2 / Zl
The equation states input impedance Zin equals the transmission line impedance (squared) divided by the load impedance. With the far end shorted, you get division by zero and Zin is extremely high, essentially open circuit.
What you will build is a quarter wave transformer. In this case, having one end shorted will appear as an open circuit at the other. As far as your radio is concerned the shorted piece of line is not there. Best way to confirm it is to build one and measure your SWR. You won't notice any difference either on transmit or receive.
The six foot length is measured from the center of the Tee connector to the first place where the inner and outer conductors of the coax meet. RG58 and RG8 both have a velocity factor of 66%. A quarter wavelength at 27MHz is 9 feet, so the shorted line should be .66 x 9 = 6 feet.
On the second harmonic, the line is now a half wavelength long. The line will appear as a short circuit for the second and other even number harmonics. You can confirm this by building a shorted line section that is 12 feet long for 27MHz. The SWR meter should peg and the receive signal strength should drop considerably when it is installed.
The 6-foot line length is for 27MHz only. At the FM
broadcast band it is considerably shorter, about 18 - 22 inches depending on frequency. Move to 14MHz and the shorted line becomes about 11' 7".
I'd like to try out one of the surge suppressors you mention. Without having one in my hands it's difficult to form an opinion. I've learned that there is a lot of useless BS given in advertising and promoting a product. It would likely cost more than the 6-foot piece of coax and a Tee connector, but would be more suitable for a station that operated over a much wider range of frequencies.
Originally Posted by BOOTY MONSTER
, get yourself a Tee connector. It gets placed along your transmission line somewhere. On the third output connect a 6 foot piece of RG58 or RG8 cable with the far end shorted and soldered together. It will ensure the entire antenna is placed at DC ground."
can you explain how that works a little more please ?
and how does that not act like a needle stuck in the coax ?
also , what's your opinion of Morgan’s M-300 Series arrestors ? Morgan Manufacturing | IMPULSE SUPPRESSORS, ARRESTORS