Ham Radio . Magnum Experimentum
Antennas, experiments, engineering and other articles of interest to radio folks.
Measurements and analysis suggest why quarter-wave stubs fail to completely isolate radiator conductors on multi-band antennas including the popular rollup 2m/440 J-Pole products. Possible improvements are shown.
Tests suggest transmission line decoupling stubs are not immune to the conductor past the stub.
Measurements reveal the effects of common mode current on the J antenna.
I measure one example of a ferrite coax choke for response over frequency to understand its suitability for VHF and UHF.
Jim (K9YC) Brown’s toroid winding recipes provide a superb RF choke balun for 30-10m using RG316 and a #43 toroid.