| Author |
Message |
    
Znut
| | Posted on Wednesday, September 11, 2002 - 6:29 pm: | 
|
I got the materials to make a balun for my antenna project. I think I'll need a 2:1 ratio because the antenna is a 2 el. quad with an approx. 100 ohm feed point at its most efficient configuration.
Can you help me figure out the correct winding and tapping? I've got the basic 1:1 and 4:1 down.
With the ferrite and wire I have I should use at least 10 wraps on the toroid.
Thanks,
Znut |
Znut
| | Posted on Thursday, September 12, 2002 - 10:39 pm: |
|
2:1 |
Marconi
| | Posted on Friday, September 13, 2002 - 11:09 am: |
|
Znut, continue to study about baluns. But, remember something you said once before, "I got farther doing just that than looking for the magic bullet."
You are not yet sure whether you really need a balun or not. Theory tells you that you do need a balun, but don't forget to think minimally. It helps keep you focused.
I would tune for resonance and match with a resonant 1/2 wave feed line, but I would stay away from a resonant line while operating this one. They tend to increase the balance problem if there is one.
You probably won't need anything at all. After looking back at some notes on some of my quad projects, you probably won't even need a matching device for the two element quad. With the single quad element you were probably already experiencing an impedance match at somewhere near a 100 ohms due to reactance. By adding another element, you may see a lowering of this reactance, thus a bettering of match, assuming the elements are not too close or too far apart.
Add your element and try the thing like it is first. See if there is a near match and if so, work that thing a bit and see if you can tell anything in comparison from the single element.
From your picture, I noted a tree real close to the setup. It may have had some dielectric affect on the matching of the original loop. If you move the thing to a different location to make some room, be prepared to see some changes in the resonance of the driven element.
Good luck, keep it simple.
Marconi |
Znut
| | Posted on Friday, September 13, 2002 - 7:19 pm: |
|
Thank you,
I appreciate the advice and the cheers from you folks. With an antenna with some gain I'll be talking to some of you soon, I've already talked to 2 on the forum (Taz and 707). That is the main goal of this project.
I was influenced to go flatside for many reasons but my decision was catalyzed the last time I talked to Taz on the air. I was talking to him with an a-99 and he with the moonraker. Our best results were with his beam on the horiz polarity. I'm sure that maybe his ant. was better tuned on the flat, that is natural because of the detuning of the vertical by the tower/mast.
Okay, I decided to make some sort of SIMPLE antenna with some sort of directional characteristics. First I was gonna try a dipole. A fellow ham (please, no blasting about the ham part) mentioned a loop (square, delta or round) because they are very unsusceptible to terrestrial (manmade and ground) noise. It worked and has less static than I could have imagined. I made a short contact with 707 with it and was encouraging. He has an inverted L and my loop is 8 feet off the ground. So I decided to complicate things a little and make a beam and I am walking a fine line between a simple beam and one with more contraptions than the space station. You know, I want a 1:1 swr and the optimum pattern and front to back ratio of a 4 element beam.
Keep after me to have a realistic perspective Marconi! Thanks.
The frame is almost done. I was hoping to complete it this weekend but that tropical storm thing is making it rain here in GA. When it is complete I'll have some photos. Within a week or so of finishing the frame you guys should HEAR me on the finished antenna, hopefully.
Znut |
Znut
| | Posted on Tuesday, September 17, 2002 - 10:16 am: |
|
Hey,
I got some help!
"A simple balun transformer, wound as an auto-transformer, consists of a
bifilar (2) wire winding of 10 turns, with one of the wires tapped at 4
turns from the start. Connected as illustrated, the input would be 10
turns, and the output 14+ turns. This would make a 14+ to 10, or 1.4+
to 1
winding ratio. Squared, this makes a ratio of close to 2:1.
The rough sketch I've attached should illustrate the procedure.
1. Cut off an 8 inch piece of the magnet wire and set it aside. Bend
the
rest of the wire around something round like a broom handle into two
equal
lengths (not cut). Make a ribbon of the wire by the use of a short
piece of
the fiberglass tape (about 1 inch) to hold them together every 3-4
inches.
Mark the two ends with small nicks with the cutter or knife. One nick
on
one, two nicks on the other. Repeat on the other end in from the loop a
few
inches.
2. Wrap the core with the fiberglass tape - just one layer. This is to
protect the enameled wire from being damaged by the hard core.
3. Start wrapping the ribbon around the toroid, leaving about 4-6
inches
outside as leads - the cut ends.
4. Shape the ribbon as close as you can to the core with your hands
only.
Just make the turns uniform and even and keep the ribbon flat - no
twists.
Use the loop end as a leader, pulling through with a finger and then
hooking the loop over the broom handle and pulling the toroid against
the
secured end to tighten each turn. The broom can be held in a vise or
by a
friend.
5. At the 4th turn plus a bit, spread the wires a little and scrape
the
enamel off of #2 wire, baring the copper about 1/4 inch. Scrape 1 inch
of
enamel completely from one end of the loose piece of wire. Make a 180
bend
in the bared portion.
6. Hook the bared lead around the bared spot in the ribbon wire and
tighten with a pliers - then wrap the end of the loop back around the
lead
with pliers.
7. Solder the T connection and let it cool.
8. Continue the turns of the ribbon until you have 10 pretty even
turns.
9. Separate the excess ribbon and cut it in the center of the loop. Cut
the
#2 wire very near to where it leaves the core, and shape the turn to
the
core and tape it there, connected to nothing. Include the long #1 wire
in
the taping after the first turn to secure it.
10. Cut away the excess of #1, leaving about 6 inches as a lead. put a
nick
at the end so you won't forget it is the end of #1.
11. Go back to the beginning of the windings and separate #1 and #2 and
apply a piece of tape over turn # 1 to secure both wires to the core.
12. Scrape off about 1/4 inch of enamel from the beginning of #1 wire
about
1/2 inch from the core.
Prepare one end of the longer scrap wire as you did for the tap on #2
earlier, and do the same job with it on #1 with it. Mark the other end
of
the scrap with one nick.
13. Bring the end of #1 and the beginning of #2 together, scrape,
splice,
and solder. The splice should be close to the core, and each wire be
about
the same length between splice and core. The loose ends are the ground
connection on the input 50 ohm side (unbalanced). Shape one to reach
the
terminal and trim the excess of each away.
The input #1 is the "hot" side of the 50 ohm input.
The output side of #1 is one side of the 100 ohm balanced output.
The 4th turn tap is the other side.
Have fun!
73,
Press N8UG
The Wireman, Inc."
Cool, huh?
Znut |
|
