[HCARC] Baluns - Lots of Questions

[Gary and Arlene Johnson]

I guess I need to do some more research beacuase I am more confused than 
before.  Am I the only one in the club who is confused on this kind of 
thing??  I surely hope not, and I don't think so.  I guess the other 
question is how many books am I going to have to buy and read.  My library 
already has well over a thousand pages, probably working on 2000 and I still 
seem to have BASIC questions.  Maybe the secret is just to go out and buy 
some antennas or look in the book and build them exactly as specified. 
Isn't a balun that has windings the same on both sides an UNUN - whatever 
that is and whatever that is for.  It's like I found a third of a spool of 
RJ6 coax the other day that the Dish Network or whomever must have left 
here.  It's 75 ohm coax.  Not sure what to do with it, or when I could use 
it on what antenna.  How do I tell if 75 ohm coax can or should be used or 
ladder line, or TV twinlead or?????

Feeling dumb or lost in Center Point.

Gary J
N5"BAA"


----- Original Message ----- 
From: "Kerry Sandstrom" <kerryk5ks at hughes.net>
To: "Gary and Arlene Johnson" <qltfnish at omniglobal.net>; 
<hcarc at mailman.qth.net>
Sent: Saturday, August 25, 2012 2:51 PM
Subject: Re: [HCARC] Baluns - Lots of Questions


> Hi Gary,
>
>       Several years ago the ARRL published a book called "Transmission 
> Line Transformers" by Jerry Sevick.  I think it was published in 1987 
> since that is the copyright date on mine.  The ARRL Antenna Book, any 
> edition, also talks about baluns and transmission line transformers.
>
>    They are called transmission line transformers because that is what 
> they are:  transformers made from lengths of transmission line that are 
> coupled together.  A 1:1 balun is basically a 1:1 transformer that is 
> unbalanced on one end and balanced on the other.  A 1:1 balun can be made 
> from two quarter wave sections of coaxial cable.  Chapter 18, figure 6 of 
> the 18th edition of the ARRL Antenna Book shows this kind of a 1:1 balun. 
> Figure 5 of the same chapter shows a 4:1 balun made with a half wavelength 
> section of coax.  VHF guys have been using these baluns for decades.
>
>    HF baluns and transformers haven't been as popular.  You can imagine 
> some of the reasons, quarter and half wave sections of coax for 80 meters 
> aren't exactly small and light!  Many years ago, the 1950's, Heathkit sold 
> an HF balun that was reasonably broadband that consisted of a two large 
> air wound bifalar coils.  The ARRL Antenna Book 9th edition, Figure 3-41 
> shows this kind of a balun and how to connect it either for 1:1 or 4:1 
> operation. It worked from 80 through 10 meters.  They solved the 'you need 
> a different one for each band' problem but they still weren't small.
>
>    Several years ago ferrite material became available at reasonable 
> prices with good RF performance.  Ferrite is a non-linear material.  I 
> don't believe there is any linear ferrite!  When you apply one or more RF 
> signals to a nonlinear device, the device wiil generate harmonics and 
> intermodulation products from the applied RF signals.  Ferrites also have 
> some losses.  When you wind a coil on a ferrite, you will get both 
> harmonics and intermodulation products.  There is no way of avoiding it. 
> By the way, even air is nonlinear if you are running enough power.  I 
> think the power density is Megawatts per centimeter squared.  I only wish 
> I could run power like that.
>
>    "Ham Radio", an old ham magazine that has not been published for ten 
> plus years and was fondly (and not so fondly) called the Proceedings of 
> Amateur Radio  because of its technical content, had an article about 
> saturation in ferrites.  I'll see if I can find it.  I think the article 
> was primarily concerned with ferrites in a receiver front end limiting the 
> intermodulation performance of the receiver.  That should give you an idea 
> of the problem.  Several years ago one of the ferrite balun manufacturers 
> had a lot of trouble with their transmitting baluns generating harmonics 
> and causing TVI.  It is a real problem.
>
>    There are some ferrites that will operate at a higher power before they 
> cause a problem.  They are still generating harmonics, they are just below 
> the problem level at moderate power levels.  Baluns with more ferrite 
> material, larger and heavier, will handle more power generally before they 
> cause a problem.  I believe ferrite baluns that are used in high SWR 
> situations have more of a problem.  Ferrite really came into their own in 
> wideband solid state amplifiers.  Interestingly, they were running at 
> impedance levels below 50 Ohm.  The input impedance of high power 
> transistors used in wideband power amplifiers, your 100 W 160 to 10 meter 
> XCVR for instance, is very low, often as low as 5-10 Ohm.  A couple 4:1 RF 
> transformers to go from 50 Ohm to 12.5 Ohm and then to 3 Ohm were ideal. 
> 4:1 transformers to go from 75 Ohm to 300 Ohm are about the highest 
> practical impedance levels.  You can build transmission line transformers 
> that are 1:1, 4:1, 9:1, 16:1, etc.  I don't believe that there is a 6:1 
> possibility.  You can build RF transformers for any ratio you want, but 
> they aren't transmission line transformers.
>
>    You will have to find someone else to tell you aboput voltage baluns 
> and current baluns and choke baluns.  I personally think they are just a 
> lot of mumbo jumbo.  I don't use ferrite baluns much myself.  I have an 
> old Hy-Gain 15 meter yagi that uses a balun and hairpin match.  I laso 
> have a Heathkit antenna tuner that has a balun for balanced output, but 
> I've never used it. I have built some solid state transmitters that use 
> ferrite transmission line transformers to match the driver to the final 
> stage.
>
>    I'm sure thast this is more than you wanted to hear, but I don't 
> believe you can understand the issues with any less.
>
> Kerry
>
>
>
>