At the October meeting of the Cascades Amateur Radio Society, Wesley Cardone (N8QM) gave a presentation on the Siglent 1032X Function Generator. One of the things presented was the capability to use the device as a transmitter. But this is where the problem developed.
In demonstrating this capability, Wes used 50 Ohm BNC connector instrumentation coax simply attaching it to the function generator output. He measured the length of the coax and solved for a likely resonant frequency assuming a velocity factor of 0.8. There was not time to actually try it out but attendees at the meeting strongly suggested that there could be no significant radiation using coax since the shield would prevent it.
Since Wes continues to maintain that he, “…don’t know noth’n about no amateur radio, no-how,” Wes didn’t want to strongly object but merely said that he would allow for that but was not convinced. But here’s Wes’ reasoning on the issue drawing on simple electromagnetics.
First, let’s define what we are talking about. An RF signal generator is to supply a sine wave of a dialed-in frequency applicable for the antenna in use. A typical bench RF signal generator can serve as a rudimentary counterpoise in the same fashion as is common with handie-talkies. We can therefore simply attach a coax of characteristic impedance that matches the signal generator output and expect resonance when we input a signal having a wavelength four times the length of the coax, less a velocity factor.
As long as the “antenna” is resonant, that is there is no standing wave of any significance, the shield will be begin or dead wood. But when we lose resonance, a standing wave will manifest itself upon the shield and radiate with the net effect of canceling the radiation coming out of the conductor as the reflected wave increases.
Ask yourself this: What is the purpose of a choke placed at the antenna feed point for a coax feedline (unbalanced) interfacing at a balanced antenna (dipole)? The purpose is to block RF energy from coming down into the coax from the antenna. But as long as the antenna is operated only for its fundamental, and then at superlative resonance, there is no need for a choke.
But talk is cheap. Whenever we espouse theory, the theory is meaningless without an experiment as we learned from Isaac Newton. Therefore, please review the attached document which runs through an experiment to validate the above suppositions.