SWR Issue with VHF J-pole

[k9wkj]

its a jpole so it needs a choke
without one, your feedline is going to try and be part of the antenna


just a small scramble wound will make a difference

 

[nd5y]

OP needs to learn these two sayings:
"Friends don't let friends use J-poles."
and
"Only people who don't know anything about antennas use J-poles."

 

[prcguy]

Not in coax feeding a 50 ohm resistive load. None. Its what a lot of CBrs believe and talk about all the time, which is a waste of time.

if you are trying to tell me that there is no relationship to wave length and frequency hahaha you are very funny

 

[sloop]

This is one of those times when you can be both correct and incorrect at the same time. If the coax is being used as part of the antenna system (e.g. the ground plane) as is done in some limited space antenna systems; then yes, the length can have an effect on the swr and antenna performance. An example would be some of the CB limited space / apartment antennas that do not require a ground plane but do require specific lengths of coax that act as the ground plane.

 

[jonwienke]

In which case they do in fact require a ground plane, and use the feedline as a crappy kludged half-vast ground plane. That can also happen when an antenna isn't properly connected to its ground plane, and the resulting stray RF tries to use the feedline and/or mast as a substitute. That never performs well; even if you get a decent SWR, you'll have an asymmetric radiation pattern with weird lobes going off in random directions you generally don't want them.

 

[prcguy]

If the coax is designed as part of the antenna system then its length is critical. I read the other guys posts as its always critical, which its not.

This is one of those times when you can be both correct and incorrect at the same time. If the coax is being used as part of the antenna system (e.g. the ground plane) as is done in some limited space antenna systems; then yes, the length can have an effect on the swr and antenna performance. An example would be some of the CB limited space / apartment antennas that do not require a ground plane but do require specific lengths of coax that act as the ground plane.

 

[k6cpo]

The pursuit of the perfect 1:1 SWR has become a bit of an amateur radio "Holy Grail" when the difference between a 1:1 and a 1:2 is pretty negligible. The reality is that the radio isn't going to notice the difference in normal operation. My antenna analyzer doesn't even "red line" until 1:3.

 

[jonwienke]

If the coax is designed as part of the antenna system then its length is critical. I read the other guys posts as its always critical, which its not.

Feedline normally isn't, though, for the reasons I mentioned earlier. At least not for reputable antenna designs, because feedline routing isn't something the antenna design can anticipate--unlike actual antenna elements. It's definitely not part of the design for typical CB antennas used as the origin for the myth.

 

[tibadoex]

just had a lookie at the website ? is the antenna made of copper and attached to a aluminium pole ??/ If so then putt it down and check for corrosion cheers

Pole not aluminum. It's two 10' and one 5' metal antenna poles from years ago.

 

[tibadoex]

OP needs to learn these two sayings:
"Friends don't let friends use J-poles."
and
"Only people who don't know anything about antennas use J-poles."

I can't say that I agree 100% with your saying. It's an easy way to get up in the air and on the air quickly and for reasonable cost. This has worked for me since I just got my license back in June 2020.

Can't put up my Diamond X510 or Comet CHA250B until I pour my concrete. So the jpole is a good alternative until I'm ready. I can hit all repeaters in my area easily with 10 watts. Everyone said I audio sound is clear and strong. Pretty good for some copper tubing.

My NET group had a jpole meet where everyone built there own jpole. I was there but did not build one since I already have 2. Good learning experience for us all. When/If SHTF, I will have no problem building or putting up a jpole for operation if needed.

I guess it just depends how you look at it.