When tuning one of those 8" 8 turn rf chokes below the feed point is there an length of coax to leave between the 239 and the choke itself that will work best?
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RF CHOKE ?
- Thread starter Stellasstillarat
- Start date
An 8" 8 turn choke? That choke isn't tuned properly for the CB band. The CB tuned choke is either a 4 or 8 inch coil form with five winds of coax. Yes; it makes a difference. Keep in mind, that the number of turns changes the tuning of a choke's usable freq.
It is best to locate it just below the feedpoint of the antenna; the point in using one is to resist common-mode current off of your feedline . . .
It is best to locate it just below the feedpoint of the antenna; the point in using one is to resist common-mode current off of your feedline . . .
Its 5 turns of RG58 or RG213 on a 4.25" core. The amount between it and the antenna socket isn't critical but closer is better.
I certainly wouldn't form RG213 into a 4.25" diameter coil. RG-58, or RG-8x, no problem.
Rule of thumb: Bend Radius should be at least 10X the outer diameter of the coax. RG213 has an OD of 0.405" -- call it an even 0.4". Ten times that is 4 inches.
Now, since we're talking Bend RADIUS, the coil has to have a diameter of EIGHT inches. Diameter equals twice the radius.
Rule of thumb: Bend Radius should be at least 10X the outer diameter of the coax. RG213 has an OD of 0.405" -- call it an even 0.4". Ten times that is 4 inches.
Now, since we're talking Bend RADIUS, the coil has to have a diameter of EIGHT inches. Diameter equals twice the radius.
OK. Then use five winds of the LMR 400 on an 8" diameter plastic form. Make sure the winds are close together and kept in place with some tie wraps and you should be good to go. There are lots of examples online on how to do it and what materials to use.
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I've the non flex 400 and thought using four or five toung depresses cut to size and placed in iintervals and taped on the inside of the coiled coax then held in place with the wire ties would do the job and save on weight.
The fourm shown in your pictures looks great but I'd need to purchase one that's 8" in diameter and wide enough to fit the coils.. It definitely looks nice but don't know where to purchase one. Home depot? Thanks
You do not need a coil former. It looks nice but that is all it reaklly does. Probably 95% of the chokes are not wound on a former. just wind the turns neatly and tape them in place. Completely cover the thing if you want by winding the tape thru the center and around the turns on the outside. It will stay in shape for years and years.Wind it on a coffee can for shape and remove the can after taping the turns in place. Don't make something so simple seem complicated. RF won't know the difference.
What if I'm using RG6 coax?
Also I read somewhere that it was the length of the choke and not the number of turns. Trying to figure this out is getting more complicated. Still, I think it will be worth my time to actually build an antenna than too simply buy one. Hopefully it will get easier along the way.
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You're effectively making an inductor to exhibit high impedance at the frequency you're operating on so its several factors, the diameter, number of turns and spacing being the primary ones and from that therefore the length of coax used which is a secondary consideration.
Learning how to build an antenna is never a waste of time. Personally I think you'll get more satisfaction and sense of achievement out of the QSOs you make the first time you get it up and tuned than you ever will from something you bought.