One of the drawbacks with the antenna system I took to
French Island in 2010 was the time and effort to change the squid pole antenna from a 20m quad loop to a 40m ground plane. It takes about 15 minutes and that is 15 minutes more in the sun. If you need to change back then it is another 15 minutes.
![](http://4.bp.blogspot.com/-uFoIPeGXJg4/UYVhk3j0BNI/AAAAAAAABE8/KDb6seIyJ1c/s200/20m+40m+trapped+GP+diagram+small_v3.JPG)
In
January 2010 I trialed using a trap near the mid point of the main element to see if the antenna would tune and work on 20m as well as 40m. I was using my FT7 on a 7 Ah SLA battery sitting in the boot of the car.
Now, in theory this should work as I use the same principle on my
80/40/20m trapped dipole. Using one of the 20m traps from my dipole I tried a couple of wire lengths and settled on the dimensions shown above.
The trap is made with 42mm diameter PVC pipe with 9 turns of wire on it. In the middle of the pipe is a length of open ended coax acting as a capacitor. Photos of the trap under construction are below and details for making traps are
here.
With the wire lengths shown and supported by my 9m squid pole, I got SWR less than 1.3:1 on 7.100 MHz and 14.200 MHz.
![](http://2.bp.blogspot.com/-xGGvK01NMHc/TTq0CE5VNAI/AAAAAAAAARU/cQtl64HHa0w/s200/IMG_0996.JPG)
While checking the 20m SWR I heard a fairly strong signal near 14.300 MHz and, after checking my SWR was good, I tuned down and found Rick, VK2AAH, calling CQ. I answered his call and Rick came back to me with a 5 X 8 signal report into Sydney. Not a bad effort for a first contact with only 10 Watts. As the sky was getting a little dark and rain was coming along soon I didn’t talk long with Rick.
I gave the 40m band a quick look and heard Ray VK2FW calling another station. I listened and Ray called a second time. Still no answer. After his third call I called him and, after short introductions, he gave a 4 X 5 signal report. Not as good as my 20m report but I was still pleased to make a contact so quick.
By now I was starting to get wet so I signed with Ray, put on a rain coat, and packed the antenna away.
So, there we have it. A trapped vertical portable antenna for 40 and 20 m.
73
![](http://4.bp.blogspot.com/-6SWeJQFYNLQ/TxFYHKaZc4I/AAAAAAAAAcg/uh3lqU7OJjw/s200/IMG_1665.JPG) |
coax capacitor inside coil former |
![](http://3.bp.blogspot.com/-JMmxSzu8SLo/TxFW6Z-D3tI/AAAAAAAAAcQ/a4xeKcp1k7M/s200/IMG_1667.JPG) |
smaller diameter pipe inside former |
![](http://4.bp.blogspot.com/-7BZLepI3B2o/TxFZehlJKlI/AAAAAAAAAco/ex5uzeAVzEA/s200/IMG_0982.JPG) |
PVC pipes sealed with hot melt glue |
![](http://4.bp.blogspot.com/-ay1xjZx9OYA/TxFhq6A4ndI/AAAAAAAAAcw/V9TnWJHvcZ4/s200/termination+point.JPG) |
ground plane termination |
![](http://4.bp.blogspot.com/-zpmSNF2xiq4/TxFi5R6MIzI/AAAAAAAAAc4/WM0egomdc8M/s200/IMG_0451.JPG) |
ground plane termination |
![](http://1.bp.blogspot.com/-gVO6CZirTr4/Ts_zVRvwtPI/AAAAAAAAAZY/BN0JVBw0Wck/s640/trapped+gp.JPG) |
Squid pole ground plane in use – Tarra Bulga National Park (Feb 2010) |
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