I made a LFA antenna which works great at 2m, and when I connected to the Vna it works at 70cm and also at digital Tv frequencies, so I can watch tv with it!
I’ve asked this question of a couple different people and either received a flat out “it won’t work” to no response at all. It was actually your video on a new field microscope that made me ask the question. Why couldn’t a J pole antenna ( like yours pictured in this video) have the elements fitted with a rack and pinion drive and microcontroller to automatically tune the antenna directly as a transceiver frequency is selected. I watched one guy manipulate a connection in the same way this drive system would work and the j pole was tuned to each given frequency. Thanks as always for the videos and content
antennas are mechanical in nature so no reason things could not be made to lengthen or shorten with motors. be aware there are several 'J' pole designs. mine happens to have a gamma match on it. you might start with a simple vertical antenna and just move the radiator up and down.
Since your jpole is an end fed half wave fed with a quarter wave transmission line matching section it should work great on an odd harmonic. If you model it the biggest difference at 70 cm is that it has a lot more lobes, some pointing where you may not want them.
@@WECB640 good points, although a lot of things will go wrong if lightning strikes my roof: much of my house wiring goes through there. My Yaesu handi-talkie is probably the least of my worries. :-) I saw the ARRL letter about the new rules, and thanks for the pointer to the video. 73 and brgds.
It is an S11 measurement at the radio feed point. I did a measurement before with a 10ft coax and got a similar result so the cable loss is not the reason for a match, it would effect the overall efficiency of the system. The loss at 440MHz is about 3dB for the 50ft of coax.
