Toggle sidebar Toggle sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
  • Radioddity is giving away a radio for Father's Day! Click Here for details!

Jumper length.

Jim,
antennas can be a pain in the @$$ for sure. But honestly, this is how you learn, OM!

You will always have a different SWR readings in the shack if you do not isolate the antenna from the feedline. Remembering you are testing, a choke made from RG-58 or RG-213 would help you. (Just as a note, the idea is to have at least 20 dB of isolation with that choke, 30db ideally)

Again from Crawdad's link to the G3TXQ table (Link here: http://www.karinya.net/g3txq/chokes/ ):

The best choke for 11m made from RG-58 (same dimensions as the RG-213 choke) is: 5 Turns of RG-58, 4.25" inner diameter.
1746749368132.png
Below is a picture from the ARRL handbook of what you want to make. As you can see, the cable turns do not need to be perfectly side by side either. After you make it, place that sucker right at the antenna feed point.

1746749826778.png

The handbook also has notes different "Very Effective" chokes, in the pic below. Just information for you:
1746750068536.png

Keep trying !!!!
Michael
 
Awesome. Thanks Michael. I have a local giga parts not too far from where I work . Going to head over there after work tomorrow and pick up 213. Still have to figure out a power supply for my main amp. Working 6 10 he shifts leaves little time to experiment. But I’ll update results when I can.
 
2 Quick question for the group.
1: Is there a way to check for unwanted RF on a coax shield?
2: Will placing clip on ferrite beads at the meter show a response on the SWR meter if there is?
 
Got my chokes built and installed. 1.1 on ch1 1.25 ch40. Tuned it about 10 ft off the ground. Before the chokes just raising it to the 40ft height would make a huge difference in SWR. Now it’s the same at any height. I haven’t tried the shorter jumpers yet but I suspect it will be fine now. Thanks each and everyone of yall. So much help.

Cheers.
IMG_9758.jpegIMG_9760.jpegIMG_9756.jpegIMG_9757.jpeg
 
  • Like
Reactions: Shadetree Mechanic
Basically what you have to remember is that if altering the coax length or touching it alters the SWR it means your coax is forming part of the antenna. That's often because there is an insufficient RF ground/counterpoise at the antenna end of the coax so the antenna system is using anything it can to compensate and that's usually the coax. If you're using a metal pole the antenna is mounted on and it's an odd 1/4 wavelength then it'll prefer that as current takes the path of least resistance and something that is a 1/4 wave long will have the least resistance. Thats also why you use a RF choke at the antenna end so it appears as high impedance and the unwanted RF goes elsewhere.
 
  • Like
Reactions: AudioShockwav and The DB

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom