All of this discussion becomes badly confusing by failing to describe
these circuit elements by their real name. The word "balun" is a bastard
-- it is widely used to describe nearly a dozen things that are VERY
different from each other.
W4TV got it right by adding the correct description, and this post
starts to get at it, but adds another bastard word, unun.
Two-windings that are coupled by a magnetic field are a TRANSFORMER. If
the two windings have a terminal in common, they are an
AUTO-TRANSFORMER. A coil of coax is a common mode choke (and not a good
one). A section of transmission line wound around a ferrite core is a
COMMON MODE CHOKE, and if well designed (choice of ferrite material,
number of turns) can be a very good one.
Transformers and auto-transformers transform impedance by virtue of
their turns ratio. Arrays of common mode chokes can also be used to
match circuits of different impedances.
Last I looked, there was no description of the Elecraft "balun" telling
us what it is. Perhaps Eric or Wayne could add that to the catalog
listing for it.
Another point. SWR is NOT an indicator of how well an antenna works.
High SWR DOES increase loss in a feedline, but that matters only with
long feedlines and small diameter coax. That does NOT matter for typical
portable (or even mobile) operation, where feedlines are much too short
for loss to matter.
A high value of SWR as seen by a transmitter DOES limit that power that
the transmitter can put into the antenna. That's where the antenna tuner
comes in -- it transforms the impedance at the transmitter end of the
feedline (or the end of a wire plugged into the coax connector combined
with the counterpoise connected to the chassis) to the 50 ohm resistive
impedance that the transmitter wants to drive.
If we make RF current flow in a wire, it will radiate. How well it
radiates depends, of course, on its orientation. A wire laying on the
ground doesn't radiate very well. :) A wire without a counterpoise will
use whatever it sees as a signal return. If that return happens to be
the earth, the earth, which is essentially a big resistor, will burn
much of the transmitter power. The "good" lengths of wire Wayne and
those spreadsheets list are simply lengths that are likely to present an
impedance within range of most antenna tuners for the bands that the
operator is likely to use.
73, Jim K9YC
On Tue,1/31/2017 7:31 AM, Morgan Bailey wrote:
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@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.
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to mbaileyc...@gmail.com
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to j...@audiosystemsgroup.com
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
