[Elecraft] 9:1 Balun AND "random antennas"

Tue Jan 31 13:50:48 EST 2017

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 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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