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JSX Ugly Balun

from Dale Kubichek, N6JSX on August 6, 2017
View comments about this article!

JSX Ugly Balun
(HF bands 1:1 RF choke)

By N6JSX/8

The Ugly Balun is not a true transforming balun but a 1:1 RF Choke. Many HAM Commercial antennas require an RF choke (Cushcraft HF A3/A4/AW3S). I’ve added it to my Hy-Gain 18AVT HF vertical getting great results. This isolation decoupling choke KC7AVA UglyBalun is very easy to make and per the article in HamUniverse.com it can be configured to connect to coax or ladder feed lines. More words are not needed the pictures/drawings will speak for themselves.

Coil electrical data:
26 coils within 7”
Resonant Fo: 0.948 MHz
Coil Q: 216
Resonant impedance: 198 K
Trap inductance: 154.1 uH
Shunt capacitance: 182.7 pfd

Construction items:
26 coax (RG-8x) coil turns (~33’ of RG-8x) w/PL259
Hot glue gun & electrical tape
4”x 12” PVC
SO-239 barrel ~1.25” long w/nuts
Brackets 2ea (as picture) Lowes 2x4 Simpson Strong-Tie model RTU2
1”x¼-20 bolts 2ea
Radiator clamps 2ea


JSX-UB mounted to my tuning mast

© 2013, N6JSX/8 Sidney OH
All right reserved – only non-profits may copy or reprint.

Member Comments:
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JSX Ugly Balun Reply
by KC3JV on August 6, 2017 Mail this to a friend!
How about the good old Collin's BALUN. It is much smaller and gives you very good balanced to unbalanced 50 Ohm coax.

Mark KC3JV
 
JSX Ugly Balun Reply
by K7NSW on August 6, 2017 Mail this to a friend!
Sounds good to me. So where do I get a good old Collins balun which is much smaller?
 
RE: JSX Ugly Balun Reply
by KC3JV on August 6, 2017 Mail this to a friend!
You have to make one yourself. It uses coax so I assume its for a 20 M through 10 M beam?

I will send you directions.

Mark KC3JV or look up Collin's BALUN on the WEB
 
RE: JSX Ugly Balun Reply
by W5DXP on August 6, 2017 Mail this to a friend!
What is the choking impedance at the frequencies on which it is used? The closest I could come to your choke on g3txq's web page is 25 turns of RG-58 on a 4.25 inch coil form. It works pretty well for 40m-20m. The choking impedance on 15m-10m is less than 500 ohms.

http://www.karinya.net/g3txq/chokes/choke_impedances.png

As one can see from the various designs, it is virtually impossible for a single ugly balun to work well over all of HF. A rough rule of thumb is that an ugly balun needs half the turns of the band in meters on which it is used, i.e. 40 turns for 80m and 5 turns for 10m.
---
73, w5dxp.com
 
JSX Ugly Balun Reply
by KQ6XA on August 6, 2017 Mail this to a friend!
If you add some ferrite beads around the coax leading to that coil, you would have a broadband coaxial choke. Or, you could put some ferrite rods inside the coil.

Viability of air-coiled coaxial cable by itself as a coaxial choke, is extremely sensitive to the lengths of cables that go into and out of it, as well as the frequency of operation.

Ferrite provides "HF-resistance" as well as "HF-reactance" isolation.

An air coil just provides "HF-reactance" isolation.

They are not equivalent.
 
RE: JSX Ugly Balun Reply
by G3RZP on August 8, 2017 Mail this to a friend!
How much common mode impedance do you ACTUALLY need for feeding an antenna? Or rather, how far down does the unbalance current need to be to produce an unnoticeable effect at HF?
 
JSX Ugly Balun Reply
by K4RVN on August 8, 2017 Mail this to a friend!
A nicely done presentation Dale. Thank you for sharing it.

Frank K4RVN
 
JSX Ugly Balun Reply
by KD6VXI on August 10, 2017 Mail this to a friend!
I use(d) the same choke for years. Still do, matter of fact. One of these in FRONT of a ferrite choke can help the ferrite from cracking, if you are into QRO.

However, I wouldn't mount it parallel to a mast, element, etc. C Stray will cut your choking impedance way down. And since this choking impedance is inductive, you can see any C Stray will be bad juju.

Also, C stray between turns can be mitigated by using quarter or 3/8 inch rope between turns. Might make your choke bigger, but will help wide band the choking impedance.

Some say these don't work. Those are the appliance operators and regurgitaters. They DO work, built for the band (or limited, bands) you are interested in.

--Shane
KD6VXI
 
JSX Ugly Balun Reply
by E73M on August 10, 2017 Mail this to a friend!
It is amazing what sites like Hamuniverse.com propagate...same as countless BS on Youtube.

What good choking impedance your narrow self-resonant coil around 1MHz does on any HF band, especially if used on A3/A4 20-10m Yagi?
The answer is simple: NONE!

Coiled coax as choke/BALUN is very narrow and provide a high impedance (resistive) only at resonance which is very narrow especially if such great numbers of turns are used.
Even junk as MFJ-915 Choke/Balun has 10 times more of resistive common mode impedance than your nicely wound coil on any HF band.

It would be far more useful for the rest of the EHAM readers if you did your homework and researched the eHam, QRZ etc., which BTW have an enormous amount of information about Choke/Baluns and even so called "ugly Baluns".
73 Danny E73M

 
RE: JSX Ugly Balun Reply
by SWMAN on August 10, 2017 Mail this to a friend!
WOW
 
RE: JSX Ugly Balun Reply
by KC4ZGP on August 11, 2017 Mail this to a friend!

I use one of these 'pretty' baluns on my 160 meter horizontal loop.

Alrighty.

Kraus
 
RE: JSX Ugly Balun Reply
by KH6AQ on August 11, 2017 Mail this to a friend!
The choke impedance is:

160 meters 670 ohms
80 meters 268 ohms
40 meters 126 ohms
20 meters 62 ohms
10 meters 31 ohms
 
RE: JSX Ugly Balun Reply
by G3RZP on August 12, 2017 Mail this to a friend!
KH6AQ

Are those the numbers calculated from the given inductance and capacitance figures? An interesting point is what the inductance and capacitance figures are at the various frequencies.

More to the point perhaps is what the actual impedances are as measured with an RF bridge or VNA.
 
RE: JSX Ugly Balun Reply
by KH6AQ on August 12, 2017 Mail this to a friend!
Yes those numbers are calculated using the author's inductance and capacitance numbers. But, these are incorrect.

Using a solenoid inductance calculator shows the choke to have an inductance of approximately 30uH.

The G3TXQ common-mode choke page shows a similar air-cored balun (25T RG58 on a 4.25" form) having an impedance of roughly 500 ohms at 2 MHz and a SRF near 10 MHz. If we say the 500 ohms at 2 MHz is inductance only it is 40uH, which is close to the solenoid inductance calculator.

For the author's triband antenna the feedline choke could be improved by using eight turns rather than 26.

http://www.karinya.net/g3txq/chokes/
 
RE: JSX Ugly Balun Reply
by W5DXP on August 12, 2017 Mail this to a friend!
> G3RZP wrote: How much common mode impedance do you ACTUALLY need for feeding an antenna? <

A reasonably good rule of thumb is ten times the feedpoint impedance - about 700 ohms for a resonant 1/2WL dipole - about 40,000 ohms for a Double Zepp. :(
--
73, Cecil, w5dxp.com
 
JSX Ugly Balun Reply
by E73M on August 13, 2017 Mail this to a friend!
The coaxial choke/BALUN gets worse as you add more turns.It is narrow in resonance and presents reactive impedance away from the resonant point where the choke has resistive part of impedance larger than reactive.

See here how six turns of RG8X bundled in 6 inches diameter, a common balun used on most A3/A4 Yagi antennas looks like. It is working only on 12Mhz or so and useless on bands above or below.

[url]https://forums.qrz.com/index.php?attachments/6turnsrg8xon6inchdiameter-bundle-png.306092/[/url]

73 Danny E73M
Myantennas.com
 
RE: JSX Ugly Balun Reply
by WA1RNE on August 13, 2017 Mail this to a friend!
As others have stated, the design parameters for this choke are far from ultimate for 20-10 meter operation.

The capacitance between turns ruins the response of the choke as the self resonant frequency is hovering at 16 mhz.

Although still a compromise, a better design using the same cable and form could be made as follows:


12 turns of RG/8x, 4" diameter form, spaced 1/2 between turns or approximately 6" long.


The self resonant frequency of this choke is ~32 Mhz and provides:

~500 ohms of reactance at 14 Mhz

~841 ohms at 21 Mhz

~1189 ohms at 29.7 Mhz


The authors current design can be easily modified with these modifications and will make a world of difference in terms of performance.


...WA1RNE
 
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