On 8/26/2012 5:34 PM, Andrew Moore wrote: > Essentially what I want to do is to run the signal from the shack out to > the trailer and have the radiator and ground plane "start" (and split off) > there. However, I'll definitely need the tuner in this scenario, so will > having the tuner be located 100 feet before the split throw it all off, or > introduce imbalances along, say, a coax run from the shack to the trailer?
The coax WILL add some loss, and how much loss will depend both on the coax and on the degree of mismatch. HOWEVER -- the additional loss due to mismatch is often much less than many believe. There's an excellent graph in the ARRL Handbook that shows this. Some suggestions. First, ALWAYS use BIG coax to minimize the loss. You don't need a premium coax -- a decent RG8 with a robust copper braid shield is fine. Second, for both uses of the antenna, I would run coax from the rig to the aluminum frame at the point of connection, and make the shield the connection between the rig and the frame. Then simply put in a decent coax switch to change between the two operating positions. Third, once the coax to the house is hooked up, check the VSWR without the antenna tuner, then use the graphs in the Handbook to first translate the VSWR reading in the shack to the actual VSWR at the antenna, then use that value of VSWR to see how much additional power is lost due to the mismatch. If the loss is particularly high on any band due to a really bad match, tweak the length of the antenna to improve it. Most really bad matches with a long wire are caused by an antenna that is very close to an exact multiple of half-wavelengths, or by a dipole that is very close to an exact multiple of a wavelength. That's where the 44 ft vertical came from. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
