Home |
Search |
Today's Posts |
#1
|
|||
|
|||
2 Meter Choke Baluns
From what I have read there seem to be two common types of choke baluns
employed at 146 MHz, the coiled coax balun and the W2DU type with ferrite beads over the coax. Looks like other types of baluns such as the sleeve balun or a Guanella toroidal balun could also be used. Other than the obvious restrictions imposed by physical mounting arrangements, what are the advantages and disadvantages of each type. There seems to be considerable variation in the design of coiled coax baluns, with most designers advocating a few turns of coax with a diameter of 3 to 8 inches. One designer was convinced that anything over 3/4 of an inch would not be functional at VHF frequencies. Others maintain that the coil of coax should be wound on a core keeping the turns aligned, while others simply coil the coax up and tape it together. Some recommend one coax width of air between turns. With regard to ferrite beads on the coax type of balun, how many ferrite beads of what type are most effective? Some advocate that another set of ferrite beads be placed at a point below the feedpoint. Seems there is lots of latitude in construction of these types of baluns. Are they really this forgiving, or are there a lot of less than full effective balun designs? I'm trying to decide what is the best option for me, and am confused at all the variations. Darrell VA7TO |
#2
|
|||
|
|||
2 Meter Choke Baluns
"Darrell Bellerive" wrote:
There seems to be considerable variation in the design of coiled coax baluns, with most designers advocating a few turns of coax with a diameter of 3 to 8 inches. Well, one sure wouldn't want the circumference to be one wavelength. :-) -- 73, Cecil, W5DXP |
#3
|
|||
|
|||
2 Meter Choke Baluns
Cecil Moore wrote:
"Darrell Bellerive" wrote: There seems to be considerable variation in the design of coiled coax baluns, with most designers advocating a few turns of coax with a diameter of 3 to 8 inches. Well, one sure wouldn't want the circumference to be one wavelength. :-) Tie a knot in the coax, and pull tight until the loop inductance resonates with the capacitance. Always wondered if that one would work... -- 73 from Ian GM3SEK |
#4
|
|||
|
|||
2 Meter Choke Baluns
"Darrell Bellerive" wrote in message oups.com... From what I have read there seem to be two common types of choke baluns employed at 146 MHz, the coiled coax balun and the W2DU type with ferrite beads over the coax. Looks like other types of baluns such as the sleeve balun or a Guanella toroidal balun could also be used. Other than the obvious restrictions imposed by physical mounting arrangements, what are the advantages and disadvantages of each type. There seems to be considerable variation in the design of coiled coax baluns, with most designers advocating a few turns of coax with a diameter of 3 to 8 inches. One designer was convinced that anything over 3/4 of an inch would not be functional at VHF frequencies. Others maintain that the coil of coax should be wound on a core keeping the turns aligned, while others simply coil the coax up and tape it together. Some recommend one coax width of air between turns. With regard to ferrite beads on the coax type of balun, how many ferrite beads of what type are most effective? Some advocate that another set of ferrite beads be placed at a point below the feedpoint. Seems there is lots of latitude in construction of these types of baluns. Are they really this forgiving, or are there a lot of less than full effective balun designs? I'm trying to decide what is the best option for me, and am confused at all the variations. Darrell VA7TO ====================================== The first thing to do is define precisely what you want the choke balun to do and why. Then you might be getting somewhere. If you don't know, you don't need one. Then you can forget and stop worrying about it. |
#5
|
|||
|
|||
2 Meter Choke Baluns
"Darrell Bellerive" wrote in message oups.com... From what I have read there seem to be two common types of choke baluns employed at 146 MHz, the coiled coax balun and the W2DU type with ferrite beads over the coax. Looks like other types of baluns such as the sleeve balun or a Guanella toroidal balun could also be used. Other than the obvious restrictions imposed by physical mounting arrangements, what are the advantages and disadvantages of each type. There seems to be considerable variation in the design of coiled coax baluns, with most designers advocating a few turns of coax with a diameter of 3 to 8 inches. One designer was convinced that anything over 3/4 of an inch would not be functional at VHF frequencies. Others maintain that the coil of coax should be wound on a core keeping the turns aligned, while others simply coil the coax up and tape it together. Some recommend one coax width of air between turns. With regard to ferrite beads on the coax type of balun, how many ferrite beads of what type are most effective? Some advocate that another set of ferrite beads be placed at a point below the feedpoint. Seems there is lots of latitude in construction of these types of baluns. Are they really this forgiving, or are there a lot of less than full effective balun designs? I'm trying to decide what is the best option for me, and am confused at all the variations. Darrell VA7TO ======================================= A choke balun made from RG-58 coax cable, centred on 145 MHz and having a high impedance over the 2 meter band has the following dimensions - 6 turns of RG-58 Length = 30 mm = 1.2" Diameter = 37.5 mm = 1.5" Measurements are between centers of turns. Make it neatly. ---- Reg, G4FGQ |
#6
|
|||
|
|||
2 Meter Choke Baluns
And for more impedance, put one every odd 1/4 wavelength... it's the
macrame choke! And then we'll start r.r.a.a. debating the effectiveness of overhand vs. sheet bend and.... |
#7
|
|||
|
|||
2 Meter Choke Baluns
43 material ferrite beads are quite effective at VHF. I would (and do)
take this route at VHF because they're more compact than a coax choke, and you don't need too many of them to get substantial choking impedances. I was pointed to this PDF (big) for impedance vs. frequency curves. http://www.fair-rite.com/newfair/pdf...log.pdf#page=1 A 2643012702 bead of the sort that fits (most of the time!) over RG-58 has a typical 1 turn impedance of 38 ohms at 100MHz according to the catalog. You can decide on an appropriate choking impedance and stack beads in the number you need. Don't worry about chokes further down the coax unless you're really having feedline radiation problems. A choke at the feedpoint will take care of RF current conducted onto the feedline. If you're getting induced currents on the feedline, get it away from the antenna! It's VHF! :-) I'm using bead baluns on my 6m moxon, my 2m and 432m yagis... I might not notice the difference without them, but I had a box of, I dunno, 800 of those 43 material beads lying around, so I'm using bead baluns for everything. I've hung around r.r.a.a. and read many posts about cracking at high power if the choking impedance is low enough that more than a few watts are being dissapated in the choke. I've also read quite a bit about conducted RF from all the junk electronics in everyone's house being kept OFF THE ANTENNA by an effective common mode choke, and this is why I'm going to keep using them whether I feel that I need a balun or not for antenna pattern. Back when my very understanding parents let me bury all my feedlines for 40 feet under the lawn to build my high-school antenna farm, I didn't worry about choking off shield currents, but now that I'm in an apartment, everything I can do to keep antenna and noise separated is going to get done. 73, Dan N3OX www.n3ox.net |
#9
|
|||
|
|||
2 Meter Choke Baluns
If you put 100 FT-43 beads around your head, you're sure to get a
migraine choke headache, I think. It'll keep the conducted common mode RF off your torso though. Still have to worry about the radiated. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Odd signal meter phenomenon | Shortwave | |||
SWR - wtf? | CB | |||
SWR - wtf? | Antenna | |||
Choke baluns again | Antenna | |||
Choke Baluns again. New program | Antenna |