J-Antenna (2m/70cm vertical)
Building a type of J-Antenna I followed a webpage of Michael Zwingl (OE3MZC).
After first test the antenna could be tuned for 70cm very well (VSWR 1:1.5) but 2m was not usable.
Another antenna was made with same measures but some cm plus of cable and was tested and fine tuned with a Network analyzer. This showed that it will work on both 2m and 70cm with good enough VSWR but is not so easy to tune in.
Therefore the shortening factor of the 240 Ohm cable should be measured first and then the length should be recalculated. This should have as result that tuning can be done rather easily and would also be managable with only a VWSR-meter.
Result of tests with network analysator between 100 and 500MHz.