On Wed,4/5/2017 11:19 AM, Randy Cook wrote:
I have mounted a remote MFJ tuner on a post about 3 feet from the antenna base. Antenna wire goes down the pole, connects to 4:1 Unun input lug, then goes via coax to tuner. Out of the tuner to a long coax run to my shack.
HOW long is important here. Lightning is not a DC event, it is an RF event, and any wire, whether coax or a #4 looks to lightning like a big inductor. Rule of thumb is that if the distance from the tower to the shack approaches 100 ft (some authorities say more than 60 ft), there's no need to bond the tower base to the house. You don't have a tower, but the physics is the same. At lightning frequencies, the impedance to earth at the antenna is probably a lot less than the inductive reactance of a bonding conductor back to the shack, and the choke adds more inductance.
I would drive a couple of 8 ft rods at the antenna base spaced at least a rod length apart, bond them together, and to the radials. the sole function of the rods is lightning protection. So is bonding. The radials are not a substitute for rods, but they will reduce the impedance to earth by virtue of their capacitance to earth, which will be in parallel with the rods. The choke should be at the tuner on the coax going to the shack. There should also be a lightning arrestor there.
Choke at the rig end of the coax run.
It's OK to have a choke at the rig end, but it's FAR more important to have one at the antenna.
Radials mount on ground connection lug on the Unun.
It's not clear to me whether your unun is step up or step down, and you didn't say what band(s) you want this antenna to cover, but I would put the radials on the antenna side of that unun.
I was a bit confused with the tuner wiring. The manual says to connect ground lug to the ‘system ground’, I assume that means the radial collection point.
The instructions assume the tuner is in the shack. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
