[Milsurplus] 1:4 Balun

[Mike Feher]

I have received a lot of off the list email asking me to describe my balun.
Unfortunately my memory is not that great. As I said I built it about 20
years ago and do not remember the details. You could say, well easy, just
look at it. Well, that is not so easy, because when I build some things, I
make them so they will last and this balun's details cannot be seen as it is
encapsulated in foam. I built it into a small, milled aluminum chassis that
I had along with its nice cover. I remember using a toroid and a small
diameter Teflon coaxial cable to make the unit so more than likely it is a
copy of one of Jerry Sevick's designs or its derivative. This is a rather
small assembly as I was not interested in using it for high power, but for
use with my smaller military rigs that liked to see 10 to 12 ohms for the
antenna. The "4" end or what I call 50 ohms is connected to a female BNC and
the "1" end is connected to 2 binding posts, one black and one red. They are
on the opposite ends of the box. Since these type of designs are relatively
impedance independent, but provide an impedance ratio for matching, I just
figured I would use a 4 to 1 backwards. Usually the "4" end goes to the
higher impedance balanced antenna line and the "1" goes to the rig at
typically 50 ohms. Well, connected the other way around, it will transform
your 50 ohm antenna to the 10 or so ohms preferred by the rigs intended for
short antennas. For example with the TCS, I was never able to load it
properly into a resonant antenna, I just could get no where near the
recommended plate current. Using the transformer it loaded right up to the
recommended value and by looking at the output power, I knew I was there, as
I was not loosing any power at all to speak of. Simply connect the binding
posts to the TCS and the BNC to the resonant 50 ohm antenna and all is well.
As I said mine is pretty small, so I doubt that it would handle more than 50
watts. Also, I am sure I just used some junk-box core. I just now went
downstairs to connect it up to my network analyzer and pass along the
results. Back when I built it I did not have a network analyzer, HI. The
analyzer is an HP8505A and with about 12 ohms (carbon comp.) on the binding
posts I obtained the following results:

14.4 MHz:  -10.3 db return loss = VSWR of 1.9
 7.3 MHz:   -15.5 dB return loss = VSWR of 1.4
 3.8 MHz:   -20.0 dB return loss = VSWR of 1.2
 2.0 MHz:   -20.0 dB return loss = VSWR of 1.2

All of these numbers are acceptable. By about 20 Mhz the return loss was 6
dB, but I never intend it to use it that high in frequency, but with careful
building techniques, and proper core selection, I am sure acceptable results
can be obtained to much higher frequencies.

So, look in the ARRL handbook, or one of Jerry Sevick's books, or the many
articles published in QST over the years on baluns, and I am sure you will
not have any problems and will find loading that military rig into a proper
antenna much easier. John Nagle (SK), a good friend from the past, also had
a good article about baluns in QST some time ago. I shared my finding with
Walt Hutchens way back then, I think before ER started, and I believe Walt
did mention it in one of his articles that he used to publish. Sorry for the
lot of words with very little detail, but I am sure if you are resourceful
enough you will find a method that will work for you. 73 - Mike






Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ, 07731
(732) 901-9193