The zombie j-pole thread rises again. It won't die.
Consider the following:
1. J-poles are also called end fed Zepps. They are half wave antennas with a quarter wave matching section. Why? An end fed half wave antenna has (theoretically) an infinite impedance. The quarter wave section inverts that impedance to something like 50 ohms.
2. A j-pole can be either direct fed (open stub) like the Arrow antennas. Yes, they are really j-poles. Or, a j-pole can be shunt fed with the bottom shorted and the feed point moved up the matching section a bit.
3. Either design is perfectly valid. However, the open stub is the only configuration that can be directly fed with coax. The shunt fed j-pole antenna presents a balanced load and needs a balun. Connecting coax directly to the shunt feed is asking for problems and this is why many operators don't like j-poles.
4. The balanced feed concept in mostly ignored and/or hotly disputed. Don't like the idea? Don't build a j-pole and blame the antenna. Don't blame me for telling you how j-poles work.
By the way, I'm sure Arrow Antenna would be happy to hear your views on their products. Clearly they know nothing about antenna design.
Back to the present issue. Open stub j-poles are great, but they are difficult to design and are nearly impossible to tune since there is no adjustment point other than changing the lengths of the elements. So the first question is, did you know what you were doing when you changed the center frequency to 160Mhz? How did you arrive at the element lengths? If there is a problem here, you will not be able to recover no matter what coax you are using. Arrow actually knows how to make these antennas. I've tried the same thing as you and never totally succeeded.
You might be better making a shunt fed j-pole. Use a coaxial balun - not a choke and I guarantee that you will get better results. The balun solves issued with weird patterns, interaction with nearby objects and problems with resonance. Certain folks out there will dispute this. They should not use j-poles. By the way, I discussed this with a friend who has been a ham for over 50 years, has built many j-poles and has a Phd in electrical engineering. His advice is that of course you need a balun.
How to make a coaxial balun? Look in the ARRL Antenna book.
Good luck.
Consider the following:
1. J-poles are also called end fed Zepps. They are half wave antennas with a quarter wave matching section. Why? An end fed half wave antenna has (theoretically) an infinite impedance. The quarter wave section inverts that impedance to something like 50 ohms.
2. A j-pole can be either direct fed (open stub) like the Arrow antennas. Yes, they are really j-poles. Or, a j-pole can be shunt fed with the bottom shorted and the feed point moved up the matching section a bit.
3. Either design is perfectly valid. However, the open stub is the only configuration that can be directly fed with coax. The shunt fed j-pole antenna presents a balanced load and needs a balun. Connecting coax directly to the shunt feed is asking for problems and this is why many operators don't like j-poles.
4. The balanced feed concept in mostly ignored and/or hotly disputed. Don't like the idea? Don't build a j-pole and blame the antenna. Don't blame me for telling you how j-poles work.
By the way, I'm sure Arrow Antenna would be happy to hear your views on their products. Clearly they know nothing about antenna design.
Back to the present issue. Open stub j-poles are great, but they are difficult to design and are nearly impossible to tune since there is no adjustment point other than changing the lengths of the elements. So the first question is, did you know what you were doing when you changed the center frequency to 160Mhz? How did you arrive at the element lengths? If there is a problem here, you will not be able to recover no matter what coax you are using. Arrow actually knows how to make these antennas. I've tried the same thing as you and never totally succeeded.
You might be better making a shunt fed j-pole. Use a coaxial balun - not a choke and I guarantee that you will get better results. The balun solves issued with weird patterns, interaction with nearby objects and problems with resonance. Certain folks out there will dispute this. They should not use j-poles. By the way, I discussed this with a friend who has been a ham for over 50 years, has built many j-poles and has a Phd in electrical engineering. His advice is that of course you need a balun.
How to make a coaxial balun? Look in the ARRL Antenna book.
Good luck.