Need a good clean, powerful radio

UOTE="handlebar, post: 4679455, member: 43746"]No never ever leave the coax half spooled up, this will cause RF choke and severely effect the performance of the radio and antenna.[/QUOTE]

This fallacy seems to be left over from a bit of opinion published as "fact" by a retired engineer from Wilson Antennas, on their FAQ pages.

First of all, a choke, usually referred to as an "RF Choke", is a device that's made to either keep common mode currents off the OUTSIDE conductor of a coax, or to keep RF off of a line that's supplying operating voltage to a circuit, like the DC supply to a plate (or collector) in an RF amplifier choke. Without that choke, some of the RF produced in that stage would wind up going into the B+ power supply. Properly designed chokes are our friends; randomly coiling coax so it will fit above a headliner does not make a choke at all, much less one that's properly designed.

The line on the Wilson page refers to not coiling up extra coax, as that would create a choke (it will not) which would reduce the RF energy going through the coax (it will not). Nothing you can do to the OUTSIDE of a coaxial cable will affect what's going on INSIDE the cable -- that's the very point of using coaxial antenna. The *only* thing you can do to the outside of a coax to the detriment of the signal INSIDE that coax is to either pinch the cable so severely that the spacing between the outside of the inner conductor gets substantially closer to the inside of the outer conductor (shield), thereby causing a small "impedance lump". That can happen either by pinching the coax in a door/frame space, or by rolling/folding the spare coax so tightly that the conductors similarly move closer together.

But a true choke, properly used, is a *benefit* to the antenna system.

BTW, that bit about using a half-wave section of coax in order to accurately read the SWR? It is valid, as long as the lengths are calculated *precisely*, taking into account the Velocity Factor of the coax and the exact frequency being measured at, because wavelength is inversely proportional to frequency. If you're not capable of calculating the actual physical length of coax to meet the wavelength formula and factor in the velocity factor (and are sure the antenna is resonant at its feedpoint), then just use whatever length of coax you need to reach from the radio to the feedpoint of the antenna. I personally leave an extra foot or so at each end so that when the inevitable constant meter-watchers keep trying different wattmeters and SWR bridges and outboard amplifiers, with the requisite unfastening and refastening of all the coax connectors, eventually ruin the connection at one end or the other of the feedline, there's enough left to install a new connector -- a couple of times, if the radio's owner tried every new trick he/she/it comes across to increase that power output by another 2% or so.

But for a given frequency, assuming one can *precisely* cut and fasten an electrical half-wave of coax, THEN the SWR as shown at the radio end will equal the SWR at the feedpoint.

But you know what's easier? Adjust the antenna's SWR with the shortest chunk of coax that will let you get out of the near-field of the antenna (like get inside the cab and close the door), tune the antenna for minimum reflected voltage, then substitute the "real" coax (the one that will reach from the antenna to the radio) . Read the SWR as shown there, WRITE IT DOWN on a chuck of tape on the back of the radio or meter, and accept what you have as a nominal best SWR. Don't fool with the antenna any further unless that known reference SWR that you wrote changes substantially.

Remember that a resonant vertical whip antenna over a flat counterpoise that's around 5% longer than the driven element in all directions from the antenna's mount point will have an impedance of around 35 ohms, so a perfect "real world" antenna will have an SWR of 50/35, or about 1.5:1. Similarly, a resonant dipole (either vertical or horizontal, as long as it's in essentially free space, will have an impedance of about 72 ohms. Again, do the math: 72/50 gives an SWR of about 1.5:1.

Just tune for minimum reflected energy on the coax, and take a moment and look RF chokes someplace other than at the old Wilson Antennas site.

/soapbox mode OFF

73[/QUOTE]
I'm impressed with your knowledge. I've met many hams over the years that don't understand the concept you just described.