This antenna with the adjustable plate for tuning can be built from type M 1/2in copper tubing for around $13 and the coax pig tail would cost around $12. The antenna, not including the coax would cost approx $25.
In the picture above I used hose clamps to clamp the coax pig tail directly to the antenna. W4TFX, Jay and I tuned the antenna for 146.400 and we had acceptable SWR of 1.5 to 1.0 between 147.330 and 146.400. On UHF we had the same SWR between 445.8 and 447.0 which makes this antenna an excellent dual band antenna for cross band repeating.
See the SWR/IMP chart below for the results.
Mounted 55 feet up a tree (the elevation at the base of the tree is 305 feet) and connected with 107 feet of LMR-400 I could hear, for the first time, the Mt Michelle Repeater in Ashville NC, that’s 145 miles as the crow flies from Columbia. Pretty impressive.
A receive signal check was performed with the help of K9DBC, Dan Lexington SC. I was listening to Dan on my Diamond X200 mounted in my attic and his signal was S3 signal report = 33, while he was transmitting I switched to this Slim Jim antenna and he was received at S9 signal report =59. Big difference.
Questions on building or tuning will be answered by Jay W4TFX or K4LLE Pete, Jay is our resident expert on this type of antenna as he has built a couple of them and the tuning can be a little squirrelly.
We all know that Amateur Radio is all about experimenting with our equipment. Jay’s eagle eye noticed an unplanned experimentation (that’s a pretty crafty why to say a mistake !) between the field picture above and the construction diagram. After we tried to tune in UHF frequencies we noticed a big SWR problem so it was time to abort the unplanned experimentation and go with what works. Can you spot the issue ?
Here are our SWR/IMP results: