Any of you guys use these on your coax ?.....
If so, how well do they work...
These things work any better than a choke..
If so, how well do they work...
These things work any better than a choke..
Any of you guys use these on your coax ?.....
If so, how well do they work...
These things work any better than a choke..
The air choke works better but it causes a lost of some rf power because you have to wound 18 ft.Any of you guys use these on your coax ?.....
If so, how well do they work...
These things work any better than a choke..
The air choke works better but it causes a lost of some rf power because you have to wound 18 ft.
The air choke works better but it causes a lost of some rf power because you have to wound 18 ft.
The air choke works better but it causes a lost of some rf power because you have to wound 18 ft.
18 feet of coax has to be wound? Offhand that sounds way off so lets see...
An air choke has five windings of coax on a 4.25 inch diameter form.
C = π * D, where
C = circumference of the circle
π = mathmatical constant pi, rounded to 3.14 here
D = diameter of the form, 4.25 inches plus the diameter of the coax, assuming .5 for that diameter, this is because we are adding the distance from the diameter to the center of the coax on both sides of the form
So...
C = 3.14 * 4.25 = 14.915
So the circumference is 13.345 inches. As has five windings around the form we take that figure and multiply by 5...
14.915 * 5 = 74.575 inches
There are 12 inches in a foot, so to convert this figure to feet we divide by 12...
74.575 ÷ 12 ≈ 6.215 feet
Taking that data and plugging that into a coax loss calculator, I used this one, we get 3.3% loss using RG-58, which would be slightly shorter than the numbers calculated above as it is thinner. That amount of loss is irrelevant, and will be small compared to other losses inthe system, such as ground losses, or simply the rest of the coax run. Change that to RG-213 and we get 1.4% loss, and if you use LMR-400 you get 1.1% loss...
Yes there is some loss, but not enough that you
I, personally, prefer using ferrite beads on coax over an air choke, however, both options can work well.
An air choke uses reactive impedance, which can be affected by things like the length of coax, and can thus in some unlucky situations they can be made less effective. To compensate such designs create a lot of reactive impedance, bu tthis also causes their coverage bandwidth to be rather narrow, although large enough to cover the CB band easily.
Chokes made from ferrite beads have some reactive impedance, but are mostly resistive which has its own advantages. They aren't nearly as affected by varying lengths of feedline, for example, and they are also far more widebanded than the air chokes mentioned above. If you are using coax that is about the diameter of RG-8, six FB-31-1020 beads do a very good job, and are what I prefer to use when possible. They go for about $2 a piece, give or take. If you are using RG-58 diameter coax, 8 turns through a FT240-31 works very well as well.
The DB