[Elecraft] 9:1 Balun

[Morgan Bailey]

Be careful in the 9 to 1 vs 4 to 1 vs 1 to 1. The 9:1 is generally an UNUN.
When you run 100 watts or less most 1kw manufactured baluns or Ununs will
take a wide variety of SWR if you are only running 100 watts. Because this
thread is I believe about QRP the amount of power dissipated due to loss is
not a factor. When you jump to 500 watts, core heating, saturation and
breakdown are a risk.

For instance, the W2AU balun that is manufactured as a center feed point
for a dipole is only rated for the power at 1:1 SWR. In the printed
literature the power rating drops off considerable as one goes to 2:1. I
have personal experience with this particular balun when an 80/40 trap
dipole was constructed using that balun and the Unadalla KW40 traps.
Operating 40 was no problem as it was nearly 1:1 anywhere we operated [CW],
but on 80 CW the bandwidth was much narrower, as to be expected and nearing
the edges when we ran 500 watts into the antenna with the balun rated at
1kw, well, it's core heated up, SWR drastically changed, heating the core
windings so much that the solder to the SO239 connecting the core to the
coax melted off. We knew that the SWR was between 2.5-3:1 on the edges of
the 80 meter range. So be careful. Additionally, I have little faith in
stick Baluns or Ununs, I personally do not believe they are nearly as good
as a Toroid constructed balun.

Ununs seem to in my experience, tolerate wide ranges in SWR. I have used a
9:1 unun and their new 52:1 transformer for end fed antennas  manufactured
by Balundesigns.com with excellent results running 800 watts CW with little
or no heating of the core and consistent results in a multiband
environment. This was done using a 43, 53 and 87 foot end fed
vertical/random wire/ inverted L and Half Square configurations. I have not
modeled the pattern with NEC but I have compared it on Reverse Beacon
Network [RBN] and I am definitely getting out. Full well knowing that Non
resonant antennas are not as good as resonant ones, yes there is a
difference in RBN reporting which favors the resonant, but, not always.
This is because there is "funky lobe radiation"  that can give a high
report to just random one or two reporting stations and then the rest are
10-15 db less than the resonant over a wider area of report stations. This
supports the pattern is not predictable, or as predictable as a resonant
antenna installed correctly. Knowing we are addressing compromise
installation for multiband usage, this I believe is acceptable. If you have
goals of working or covering with gain and directivity, then there is no
replacement for well designed and well installed resonant antennas. This is
especially true in the competitive environment of contesting.

When an antenna that is not balanced is used, the RF will seek a way to
ground. Problems with feed line radiation, and RF in the shack are
problematic. Using a counterpoise or limited radial system is recommended
to provide the missing balance and a path to ground. This is generally not
a problem at QRP levels but because a few 100 miliwatts  of power coming
back to the shack does not cause much problems but, jump that up to 10 or
100 watts and problems will surely make your life a living hell trying to
keep the computer, keyboard, mouse cables connected and ATU from resetting
and starting tuning cycle again and again. Best solution is to run resonant
balanced antennas if one can, if one can't, invest in a few line isolators
for the coax before it hits the shack and then have a good stock of Mix 31
ferrite beads for each cable in the shack, eg, usb, keyer, mic, speaker,
keyboard, mouse...you get the idea.

In the end, when one runs QRP power, balun/unun saturation and performance
degradation, allows most anything to fly, jump the power to 100 watts,
watch out, then to 800 watts...reforming injection formed plastic is in
your future. Although, relative to this discussion,  making an unun or
balun with a T25 core and 32gauge wire will most likely produce the same
disasterous results with 10 watts. LOL.

Finally, Any antenna is better than No antenna.

Morgan NJ8M

On Tue, Jan 31, 2017 at 12:59 AM, gliderboy1955 via Elecraft <
elecraft at mailman.qth.net> wrote:

> What are the advantages/disadvantages of using a 9:1 balun v. using the
> switchable Elecraft balun at 1:1 or 4:1 or no balun at all when using a
> random wire portable?
> Why 9:1?
> Thanks
> 73 Eric WD6DBM
>
>
> Sent on my Samsung Galaxy S® 6.
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