On 7/3/2015 10:17 AM, Ian Jackson wrote:
In message , John S
writes
On 6/29/2015 10:48 AM, Wayne wrote:
As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat
metal roof. The antenna is fed with about 25 feet of RG-8, and there is
a tuner at the transmit end.

While I'm pretty happy with the antenna, I'd like to simplify the
matching.

Thus, the question: what is the purpose of a 1:4 unun on a 43 foot
vertical? ( I assume the "4" side is on the antenna side.)

I'd expect a better coax to antenna match when the antenna feedpoint is
a high Z (example, at 30 meters), but I'd also expect a worse coax to
antenna match when the feedpoint is a low Z (example, at 10 meters).

Is that the way it works, or is there other magic involved?

I think we strayed off the path to answering your original question.

The short answer is that you are correct and there is no magic
involved. A bit longer answer is:

A 43ft vertical will present a feed impedance of 1010 + J 269.2 ohms
at 30 meters. Using a 1:4 transformer at the feed point will reduce
that to 253 + J 67 ohms. That is a bit closer to your 50 ohm line.

A fixed-tuned TX will still need a matcher.


That was not part of the original question(s).



At 10 meters, the antenna will present a 147 + J 133 ohms impedance. A
1:4 transformer will reduce that to 37 + J 33 ohms.

A fixed-tuned TX will probably be reasonably happy with a direct
connection - although maybe even happier with a series capacitor of -J22
ohms.

That was not part of the original question(s).

There are several disclaimers I could include, but I think you
understand that the answers cannot be exact with the info presented.

I hope this helps.

The question is really whether the losses with the 4:1 transformer, plus
those of any matcher at the TX end, exceed those when there is no
transformer (but with higher loss on the coax), plus a matcher. Put
another way, for short feeder lengths, is it better to use the transformer?

That was not the question he asked. Please re-read the OP. I was trying
to address his original question(s) as best as I could. In addition I
also said that there were "several disclaimers I could include" which
may involve your personal concerns. I did not want to muddy the waters.

I think I answered Wayne's question(s), but I will wait to hear from him
to see if that is so.