"Roll up" J-pole in plastic PVC - why the high SWR?

Status
Not open for further replies.

wbswetnam

Member
Joined
Oct 11, 2005
Messages
1,799
Location
DMR-istan
I have made several "roll up" J-pole antennas out of spare RG-8X coax and 300 ohm TV flatlead. I get low SWR almost every time, following this video by Dave Tadlock KG0ZZ: https://youtu.be/ql6zWMZ1dEU However, every time I have tried to fit one inside a plastic PVC pipe, the SWR shoots up to 5.5 or more. I'm certain that the antenna isn't getting kinked up inside; so is it the PVC material itself? I'd have thought that plastic wouldn't affect the radiation pattern significantly.
 

NDRADIONUT

Member
Database Admin
Joined
Jan 9, 2005
Messages
1,952
Location
FARGO ND
The lower psi white pvc has the least effect on rf and the gray pipe is bad for rf....
 

SteveC0625

Order of the Golden Dino since 1972
Premium Subscriber
Joined
Oct 24, 2009
Messages
2,795
Location
Northville, NY (Fulton County)
Look up Ed Fong on the net. He makes and sells the j-pole. His instructions are to use Schedule 20 white pvc pipe. You should encase enough of the coax in the PIPE so that your mounting system doesn't interfere with the antenna.
 

SCPD

QRT
Joined
Feb 24, 2001
Messages
0
Location
Virginia
There's a velocity factor to take into consideration when putting an antenna that works fine open air, into a pvc pipe. I'm not going to look it up, but for some reason I think it needs to be shortened to 68% of it's open air length. I'll bet if you google something like "pvc j-pole velocity factor" you'll see what I'm talking about.
 

TheSpaceMann

Member
Joined
Apr 3, 2014
Messages
1,333
Look up Ed Fong on the net. He makes and sells the j-pole. His instructions are to use Schedule 20 white pvc pipe. You should encase enough of the coax in the PIPE so that your mounting system doesn't interfere with the antenna.
I have one of those Ed Fong PVC J-poles, and it is an excellent antenna. For $20 some odd bucks, you can't beat it!
 

Aero125

Member
Joined
Feb 1, 2015
Messages
210
Location
Los Angeles, CA
Ed Fong makes 2 types of the j-pole antennas. DBJ-2 is meant to be a roll up used with no PVC pipe, just unroll and hang from something. The other is the DBJ-1 specifically designed to be installed inside schedule 200 (200 psi) PVC and it is tuned for that thickness of pipe. If the wrong type of PVC is used, or if you stick the roll-up only model in PVC you'll not get the good results that these antennas are known for. These antennas work great and are very reasonable. Google them!
 

SteveC0625

Order of the Golden Dino since 1972
Premium Subscriber
Joined
Oct 24, 2009
Messages
2,795
Location
Northville, NY (Fulton County)
Schedule 20, not 200. The higher the Schedule, the thicker the wall of the pipe. (Don't believe me? Look it up before you respond.) It is Class 200 pipe, but is also Schedule 20. You are correct that it is 200 PSI.
 
Last edited:

TheSpaceMann

Member
Joined
Apr 3, 2014
Messages
1,333
That Ed Fong DB-1 PVC antenna works great! I've used it indoors, on balconies, and on roofs, with excellent results.
 

Chronic

Member
Joined
Nov 7, 2004
Messages
528
Its a simple task , build the antenna , insert it into the pvc and use a antenna analyzer or swr meter to tune it to the desired frequencies. Might have to lengthen it or shorten it a bit.
 

VancouverScan

Member
Joined
Dec 26, 2014
Messages
108
Location
White Rock, BC
I've used both of Ed Fong's antenna's for monitoring and I can say there is nothing better, they are so cost effective it is not worth your time and effort to do it yourself. He has a great program for his students and all the proceeds from his antenna's go back into the program. So why not buy the best for the least without any hassle.
 

TheSpaceMann

Member
Joined
Apr 3, 2014
Messages
1,333
I've used both of Ed Fong's antenna's for monitoring and I can say there is nothing better, they are so cost effective it is not worth your time and effort to do it yourself. He has a great program for his students and all the proceeds from his antenna's go back into the program. So why not buy the best for the least without any hassle.
I spoke to a ham who hoisted it to the top of an extremely tall tree on his property! He said that he's getting better results with it than with any other 2m/440 omni that he has used, including ones that were much more costly.
 
Status
Not open for further replies.
Top