ok i have a wire dipole, at the connection i just have the coax spliced and of course one end connected to one side and the other to the other side. i still have rf interference in my tv when i transmit my shack is on the 2nd floor my question is would a choke make a difference and would i be able to put that at my receiver or would i have to put it at the dipole connection and i was thinking to use a 6inch dia pole and wrap coax around 12 turns does that sound right. thanks
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Choke balun where and would
- Thread starter ih2425
- Start date
Put it at the feed point of the antenna. What you've described ought'a work. Just winding that choke on a 2 liter plastic bottle ought'a work too, less weight. Where is your dipole in relation to the TV that's being interfered with, very close? If so, that choke probably won't do any good. Certainly doesn't hurt to try it though.
- 'Doc
- 'Doc
What 'Doc said but also...
...try getting an RF attenuating power strip for your TV. The RFI might be coming in through the AC power. They sell these at Best Buy, Radio Shack, etc. It won't say "RF Attenuating" in bold letters on the package; you have to look at the fine print. It should say something like "-40db RF attenuation" or something similar.
...try getting an RF attenuating power strip for your TV. The RFI might be coming in through the AC power. They sell these at Best Buy, Radio Shack, etc. It won't say "RF Attenuating" in bold letters on the package; you have to look at the fine print. It should say something like "-40db RF attenuation" or something similar.
That choke doesn't really affect what's radiated from the antenna. It only prevents / reduces the amount of RF getting back into the shack (or the rest of the house) traveling on the outside of the coax (called common mode currents). It doesn't affect what's on the inside of that coax at all.
While chokes are not fool proof, they do tend to keep stuff off of the coax. So, placing that choke as close to the feed point of the antenna as possible means tht the coax/feed line after the choke (looking from the antenna back to ward the house) is 'clean'. The only part that isn't 'cleaned' is between the choke and the antenna. That 'cleaned' description is a bad way of saying it because the feed line won't be all that 'clean', but it will be 'cleaner' than without the choke being there, if that makes sense.
The other important thing to remember about using a coax choke is that coax can only be bent so much before it starts to be 'too much'. If you have to force it to bend, the coils are too small. A coil form about the size of a 2 liter plastic bottle is about right for RG-58 size coax. Something like a 3 pound coffee can for RG-8 size coax. How many turns? Good question! A very general answer is a coil about as tall as it is in diameter, give or take some. A little more is better than not enough, till it gets ridiculous. I don't know of any 'set' answer for any particular band. If it looks about right, it's probably about right, hows that for an answer??
Good luck.
- 'Doc
While chokes are not fool proof, they do tend to keep stuff off of the coax. So, placing that choke as close to the feed point of the antenna as possible means tht the coax/feed line after the choke (looking from the antenna back to ward the house) is 'clean'. The only part that isn't 'cleaned' is between the choke and the antenna. That 'cleaned' description is a bad way of saying it because the feed line won't be all that 'clean', but it will be 'cleaner' than without the choke being there, if that makes sense.
The other important thing to remember about using a coax choke is that coax can only be bent so much before it starts to be 'too much'. If you have to force it to bend, the coils are too small. A coil form about the size of a 2 liter plastic bottle is about right for RG-58 size coax. Something like a 3 pound coffee can for RG-8 size coax. How many turns? Good question! A very general answer is a coil about as tall as it is in diameter, give or take some. A little more is better than not enough, till it gets ridiculous. I don't know of any 'set' answer for any particular band. If it looks about right, it's probably about right, hows that for an answer??
Good luck.
- 'Doc
Update
hey i wraped 13 turns around a 5 inch plastic container and it took care of the rf back in the shack to my tv it seems to even transmit more and cleaner if that sounds right thanks everyone for helping me this is a very informative site i will be on here for any other info i might need 73
hey i wraped 13 turns around a 5 inch plastic container and it took care of the rf back in the shack to my tv it seems to even transmit more and cleaner if that sounds right thanks everyone for helping me this is a very informative site i will be on here for any other info i might need 73
Wouldn't a 1:1 current balun work just as well? Either at the transmitter or at the antenna's feed point or both. I know that winding coax is cheaper but current baluns aren't that expensive.
"Wouldn't a 1:1 current balun work just as well?"
More than likely, yes, as far as feeding a balanced antenna from an unbalanced feed line. It would probably handle the CMC thingy fine too. But since TVI/RFI isn't always because of CMC, it may or may not 'cure' your problem (same as with the choke). If the problem is caused by 'over-load', then the only thing that's really going to help is distance between transmitting antenna and the TV, etc. Or, reducing transmitter power. Both/either may not be very easy to do. Filtering the TV may also be an option.
- 'Doc
and the only sure cure I know of is to beat one'a them things to death with a hammer. Which one is your choice... (pick the TV!)
More than likely, yes, as far as feeding a balanced antenna from an unbalanced feed line. It would probably handle the CMC thingy fine too. But since TVI/RFI isn't always because of CMC, it may or may not 'cure' your problem (same as with the choke). If the problem is caused by 'over-load', then the only thing that's really going to help is distance between transmitting antenna and the TV, etc. Or, reducing transmitter power. Both/either may not be very easy to do. Filtering the TV may also be an option.
- 'Doc
and the only sure cure I know of is to beat one'a them things to death with a hammer. Which one is your choice... (pick the TV!)