1:1 or 6:1 Balun for Flat Top dipole

[VK5FACE]

Im setting up a 40m Inverted vee that i may wish to change to a flat top dipole at some point. i have been advised against using a 1:1 balun for a flat top dipole and to instead use a 6:1 as the input impedance of a flat top is around 300 ohms. However many flat top dipoles use a 1:1 balun. Im just being hit with conflicting information here. would like some clarification

[VK5ZD]

Hi

Not quite sure what you mean by a "flat top dipole". If you are referring to a conventional centre-fed dipole where the ends are at the same height as the centre (i.e. it's parallel to the ground), then stick with the 1:1 balun as the feed point impedance should be close to 50 ohms (definitely not 300 ohms).

[VK4JAM]

I recommend trying an OCF Dipole. Google "ocfdipole.pdf by bertrand vk2dq" and download the file "ocfdipole.pdf".

This will give you multiple bands, and great performance.

For a resonant half wave dipole split in the middle you should use a 1:1 Balun.

[VK2OMD]

Im setting up a 40m Inverted vee that i may wish to change to a flat top dipole at some point. i have been advised against using a 1:1 balun for a flat top dipole and to instead use a 6:1 as the input impedance of a flat top is around 300 ohms. However many flat top dipoles use a 1:1 balun. Im just being hit with conflicting information here. would like some clarification

You need to look for explanations. If someone advises you but cannot explain the reasons why, then you should have lower confidence in their advice.

If you are talking about use of an ordinary half wave dipole on one band centre fed with coax feed line, then system efficiency will usually be greatest when the feed line VSWR is lowest. The feed point resistance of a half wave dipole will range from about 40 ohms to about 80 ohms depending on its environment, height etc, and so to obtain minimum VSWR with 50 ohm feed line you would not want a 6:1 balun, a 1:1 current balun with high choking impedance would be my choice.

You can make a 1:1 current balun with high choking impedance with inexpensive parts from Jaycar, but it seems most hams elect to buy something ready made.

Above is the predicted common mode impedance of 9t on a LO1238 core (about $4 for two), the cable could be RG174 or RG316 - but it MUST have copper centre conductors, not plated steel, or WB1702 speaker twin - but that cable is not suitable above 10MHz. Coax is best as it will give best Insertion VSWR, but heed the warning about steel cored conductors, they are a fast route to QRP^2 which is "doing even less with less" to twist a QRP slogan. Yes, the chart is an estimate, but I have built and measured 8t versions and I am confident that the 9t with crossover winding will be close to the graph. This design is specific to the components mentioned.

If you are not a 'maker', and lets face it, most hams aren't, Balun Designs in the US has some good products, one of the few sellers who publish some limited Zcm data for their current baluns, and which you could get here for around $100 give or take.

Owen

[VK4WDM]

Hi Andrew

Like Owen said, baluns are not hard to make yourself, but just be careful of the connections. make sure they are correct and are properly soldered e.g no "dry joints."

A 40m dipole will also work very well on 15m, and if you add a 10m dipole to the same feedline (making it "what is commonly called a "fan dipole") you will get good results on 40, 15, and 10m.

An off-centre dipole also works well but you need to do some reading first because there are different baluns recommended depending on the height of the antenna (there are several threads on OCF antennas).

Playing with wire antennas is a fun part of ham radio, but remember it can be very addictive and you can become a TAWAN, a totally addicted wire antenna nut for which there is no cure

73

Wayne VK4WDM

[VK2AVR]

One more thing to bear in mind, if trying to build a balun make sure you source the exact same core that a published design has used. Substituting a random core without careful consideration/analysis *will* result in a dismal failure. However, when you follow a design properly then homemade baluns can work exceptionally well. As you start to learn more about balun design (and it is a complex topic) you will start to understand how they work. That in itself is a good learning experience, although I admit sometimes you just want to get on air with a minimum of fuss

[VK4WDM]

sometimes you just want to get on air with a minimum of fuss

OK, put it up without a balun until you make or buy one. That will make the purists among us choke on their cornflakes, but baluns are a relatively new innovation and for the first half of my ham-life there was no such things as baluns. The feed line was attached directly to the coax. Ok, modern rigs are a bit more choosy about impedance matching, and an antenna with a balun will be a tad more efficient than one without, but it will still work. (Personal confession - the dipoles I put up when I first moved to this QTH three years ago did not have baluns, I did not have any to use, but I put a couple of ferrite beads on the coax close to feed point to reduce common-mode currents on the feed line).

If you want to buy rather than home brew the Comet and Diamond brand baluns work just fine for me and you get them on Ebay much cheaper than the "high end" ones from the USA.

Get the antenna up and operate and refine it as you go along

73

Wayne VK4WDM

[VK2OMD]

The original posting was asking advice on a balun... and the thread winds up at the "any antenna is better than no antenna" destination.

It is an overly technical thread, as most hams wouldn't really understant what a balun does, the distinction between a voltage balun and a current balun, and how to assess whether a balun "works" whatever that means.

Owen

[VK2AAH]

A balun is such a simple device and concept... why on earth would an amateur not use one & do things properly in the first place? I can't fathom it... it isn't like they are expensive, or hard to make, or hard to get... the only excuse I can find for not using one after having the basics explained is laziness. I can only shake my head...

And a new concept Wayne? Really? The personal computer is modern... The VKLogger forum is modern.... but a balun? OK, if you date back to Hiram Percy Maxim the balun is a modern concept...

Cheers

Richard
VK2AAH

[VK4WDM]

Hi Richard

I am NOT saying don't use a balun. What concerns me is that some hams strive for perfection first and then start to operate. Get an antenna up and a signal on the air and then optimise the setup. Why delay the fun even for a couple of days (or hours) . When you have the balun sorted pull the wire down and attach it.

I went portable for a couple weeks last year and forgot to bring the antenna and feed line. No problem. Went down to the hardware store brought some twin lead, split it to the length of a 40m dipole, tied a knot, used the remainder of the twin lead as a feed line, stuck one end in the coax socket of the antenna tuner, the other connected to the earth terminal, trimmed for best SWR, no balun, no coax, not even a coax plug World's best practice? Course not? Optimum setup! No! But it worked OK and I got contacts all over the place.

Baluns are comparatively recent. Never even heard of them in military comms in the 1960's, 1970's and early 80's and my guess that most hams did not use them then either. They really only became needed when we went to solid state finals that are a bit more sensitive to to match.

Remember the old saying: any antenna in the air (even a balun-less one) is better than the antenna you are just talking about.

73

Wayne VK4WDM

[VK6OX]

Hi Richard

I am NOT saying don't use a balun. What concerns me is that some hams strive for perfection first and then start to operate. Get an antenna up and a signal on the air and then optimise the setup. Why delay the fun even for a couple of days (or hours) . When you have the balun sorted pull the wire down and attach it.

I went portable for a couple weeks last year and forgot to bring the antenna and feed line. No problem. Went down to the hardware store brought some twin lead, split it to the length of a 40m dipole, tied a knot, used the remainder of the twin lead as a feed line, stuck one end in the coax socket of the antenna tuner, the other connected to the earth terminal, trimmed for best SWR, no balun, no coax, not even a coax plug World's best practice? Course not? Optimum setup! No! But it worked OK and I got contacts all over the place.

Baluns are comparatively recent. Never even heard of them in military comms in the 1960's, 1970's and early 80's and my guess that most hams did not use them then either. They really only became needed when we went to solid state finals that are a bit more sensitive to to match.

Remember the old saying: any antenna in the air (even a balun-less one) is better than the antenna you are just talking about.

73

Wayne VK4WDM

You're a ham after my own heart Wayne! The "raison d'etre" for me becoming a ham in the late 70s was the excitement and thrill of"home brew" and experimentation. Mucking about building baluns is part of it. Putting it all together, so to speak, and finally reaping the fruits of that experimentation by actually having a 2-way communication with another Ham was, and still is, my prime reason for "hanging around".

[VK2AAH]

Wayne when I was a kid my first transmitting antenna that I made was a 1/2 wave dipole and I used it without a balun because I didn't know that they were needed. Now looking back at the TVI I caused even at modest power levels when using that antenna I realise that I was following the saying "any antenna is better than no antenna", though I'm not sure the neighbors would agree! If someone knows that a very simple device would avoid this from potentially happening I see no excuse for not doing it the right way...I was a technically naive kid but people on this forum have access to people with loads of experience & knowledge & a willingness to share- they are miles ahead of where I was at when I was starting out.

Make a balun, buy a balun... but don't excuse slackness in this day and age...

Cheers

Richard
VK2AAH

[VK4WDM]

I not promoting slackness, I am suggesting a pragmatic approach to get somebody on the air until something better is organised. I very much doubt if 10w is going to cause TVI in today's digital world, balun or no balun, and did you note the recommendation to use ferrite beads on the feed line?

And no, my ad hoc portable setup did not cause TVI even though the TV antenna was less than 1m away from the transmitting antenna

73

Wayne VK4WDM

[VK4WDM]

Andrew

I have a spare 1:1 balun I can send you for free. Call book address OK? (That will get Richard off my back ).

73

Wayne VK4WDM

[VK3YE]

A balun is such a simple device and concept... why on earth would an amateur not use one & do things properly in the first place?

Because there is elegance and beauty* in doing stuff with the least possible. A balun is unlikely to make much of a difference with say a portable dipole and QRP rig.

(*) Note though that it is possible to argue that the amount of beauty or tidiness in the world is constant, and an attempt to beautify one thing invariably has an effect on other things. Eg every pretty planned city breeds uglier development over the border. Elegance due to the lack of a balun may breed a distorted radiation pattern etc.

[VK2AAH]

I didn't know I was on your back Wayne... that's what God created wives for...

VK3YE... no argument about portable operation but for a permanent installation? And it is quite surprising how much interference can be generated with relatively low power when it is being radiated from the coax. Simplicity is one thing but surely trying to do things right is another?

Cheers

Richard
VK2AAH

[VK2OMD]

Andrew

I have a spare 1:1 balun I can send you for free. Call book address OK? (That will get Richard off my back ).

That is generous Wayne, but also imposes your values of what makes an effective balun.

Most commercial baluns are voltage baluns, and good voltage baluns tend to drive equal but opposite currents into symmetric loads, and only symmetric loads (it is a by product of their tendency to drive equal but opposite voltages on their output terminals).

Whereas good current baluns tend to drive equal but opposite currents into all loads.

Whilst some antenna systems might present quite symmetric loads, not all do and even centre fed dipoles can be quite asymmetric as a result of their environment.

I am the first to concede that a balun is not 'necessary', meaning that a station will get QSOs if that is the objective, and lack of a balun will not prevent that, nor will lack of a balun necessarily degrade their chances. In the new dumbed down minimalist ham radio where making contacts has largely replaced the desire for understanding, it is hard to argue to most people that the QSO / DX QSL test is not simple and valid.

However, that concession is not to say that an effective balun is a waste of time and money.

A deeper understanding of what makes an effective balun and its effect on receive and transmit performance, and wider consideration of the benefits of not initiating an interference history with neighbours and family might lead to a more cautious approach that the "I don't need no stinkin balun" rather cavalier approach that many hams espouse.

Whilst current baluns are not new (Guanella described his current balun 70 years ago), hams are slow on the techology uptake and whilst current baluns have grown in popularity in the last 10 years, almost all general purpose HF ATUs commercially available today incorporate a voltage balun even though it is less suited to the intended application. That lack of technology awareness means that if a balun is not identified as a current balun, it is probably a voltage balun.

I remember the days when Dick Smith stocked an Amidon or knock-off balun kit that had a red #2 powdered iron core and instructions to wind a Ruthroff voltage balun. The design was poor for many reasons, inadequate magnetising impedance for the lower HF bands, and poor suppression of common mode current on assymetric loads. No wonder lots of hams formed the view that baluns didn't make a difference. Today, this design still has its supporters who argue that a low loss powdered iron core has to be better than a lossy ferrite core, but they argue it without reliable experimental data or theoretical analysis... that is mostly the way of ham radio.

Owen

[VK2AAH]

http://www.hamradio.com/detail.cfm?pid=H0-008703

For about $50-60 landed you can get one of these from HRO... clearly marked 4:1 current & rated to 1500W (should meet most VKs power requirements...).

Just for the general information of those who are looking at such new antenna technology....

Cheers


Richard
VK2AAH

[VK5ZD]

Hi

And it is quite surprising how much interference can be generated with relatively low power when it is being radiated from the coax.

How does RF radiated from the coax cause interference? Surely all that happens is the radiation pattern gets modified a bit; not having a balun isn't going to generate any extra frequencies. An example would be a G5RV which is designed to radiate from the feed line yet these are not renowned for causing interference.

[VK2OMD]

... An example would be a G5RV which is designed to radiate from the feed line yet these are not renowned for causing interference.

Can you refer to anything written by its designer that supports the above proposition?

Owen