"Tom W3TDH" wrote in message
...

On Monday, June 29, 2015 at 8:46:47 PM UTC-4, Wayne wrote:
"Dave Platt" wrote in message ...

In article ,
Wayne wrote:
So, lets begin again, with no distractions.

What is the purpose (or benefit) of using a 1:4 unun on a 43 ft
vertical.

# http://www.eham.net/articles/21272 has a nice analysis.

# It looks to me as if:

# - Without a 4:1 unun, the antenna provides a very nice match at three
# frequencies with in the HF band. At other frequencies, the SWR is
# up over 10:1 much of the time - high enough that a coaxial feed
# can be rather lossy.

# - With a 4:1 unun, you do lose the excellent match at those three
# frequencies... but the match gets better at most other
# frequencies. The SWR across the HF band is much more uniform, and
# lower on average... low enough to cut the coax losses somewhat and
# (I think) within the matching range of many rigs' "line flattener"
# built-in autotuners.


Thanks Dave. I'll have to spend some more time studying it, but the
article
is along the lines of what I was looking for.

I would assume that the 1:4 causes behavior just as you say....worse SWR
at
nearly matched frequencies and better SWR elsewhere.

I'll have to pull out some textbooks and see how the math works out for a
Z
seen through a 1:4 unun.

In practice, I've had good results with SWRs even in the 30:1 range with
short coax feeds.

More research...and thanks.

# I know that what I am about to say is provocative to some but I still
think it is worth saying. If you look at the way that commercial and
military radios are matched to antennas you will notice that most of the
matching is done as close to the # feed point as practical.

# Since only the power that actually reaches the antenna can be radiated I
have a hard time seeing the point of matching the transmitter to the feed
line. Matching at the feed line connection point will prevent damage to the
transmitter but if # that were the main objective a dummy load would
accomplish that.

# When you couple the antenna to the load at the feed point you can have
extremely low losses in the feed line. When you do the matching at the feed
point you will transfer the most energy possible to the antenna and will get
the highest # available effective radiated power. Since the objective is
the transfer of the highest practical amount of power to the antenna the
place to do that is at the feed point were possible.

#I do realize that it is often simpler and easier to match at the feed line
connection but I felt obliged to point out that is is not the most effective
place to do the job.

I agree. However, the extra trouble of matching at the antenna feed point
may not necessarily provide a noticeable improvement.

On one of my antennas, I just provide a conjugate match for the
antenna-feedline at a tuner within the shack. Then I accept whatever
additional loss there is in the coax.

For my 25 foot run of RG8, there is about 0.5 dB of loss with a match at 30
MHz. From the charts, there will be about an additional 2.7 dB of loss if
the SWR is 20:1. For a 10:1 SWR the additional loss is around 0.9 dB.

Below 30 MHz, the numbers get smaller.

Of course, my automatic tuner (in the shack) fizzles out around SWR 5:1, but
my manual tuner can be used instead at higher SWRs.

In the case of the 43 foot vertical, it seems to me that a conjugate match
in the shack would still be optimum, but perhaps not significantly
beneficial.

On the 43 foot vertical it could be that the 4:1 unun provides a lower
amount of SWR induced additional feedline loss on high Z feedpoints. Of
course, the unun might increase the SWR induced additional feedline loss for
smaller Z.

That's why the original question, and what I'm trying to understand.