On Sun, 05 Jul 2015 20:22:19 +0100, Brian Reay wrote:

As for a simpler way, I'd recommend a remote auto-matcher like an SGC at
the antenna base. It will minimise coax losses and should give you a
good match, at least for most bands. I've used a similar set up (with
radials) and achieved a good match even on 80m.

If your radio has a built in tuner, then it can be used to 'tweak' the
match in the event the radio isn't 'seeing' 1.5:1. Turn it off
initially. Let the SGC find a match. If it isn't ideal, use the local
ATU for a final tweak. I never found this was required but YMMV.

Not everyone is a true believer in antenna tuners:
http://www.qsl.net/g3tso/Hombrew-Mobile%20Antennas.html

I've done some admittedly crude testing of various matching
contrivances by measuring the resultant field strength for a given RF
power level (measured at the antenna connector). Although not
conclusive or spectacular, the early model automagic antenna tuner was
rather lossy.

Incidentally, I contrived a rather crude but effective way to measure
relative overall efficiency. I measured the power consumption from
the AC line with a Kill-a-Watt meter (in watts, not VA) and adjusted
the CW RF output for some reference level on the field strength meter.
While this would not give me a real number for the efficiency, it does
produce relative numbers for comparing antenna matching devices.
Unfortunately, I can't find my results, but I do recall that the
winner was a simple 4:1 torroidal matching xformer.

Remember, you really want a low SWR for two reasons, one because modern
radios demand it but also to reduce coax (or feeder) loss. With an
matcher at the antenna feed point, coax losses are minimised. An ATU at
the TX end does nothing to reduce coax losses in real terms.

Coax losses below 500 MHz are mostly in the I^2R losses of the copper
(as limited by skin effect). Above 500MHz, the dielectric gets
involved. See Fig 4:
http://www.maximintegrated.com/en/app-notes/index.mvp/id/4303
Higher RF currents, caused by low impedance terminations, will cause
higher I^2R losses. These higher losses are why very low impedances
are not popular for RF power devices. This has NOTHING to do with
matching. For a given RF current through the coax, the contribution
of the coax to overall losses will be independent of the VSWR.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558