delara newsDelaware Amateur Radio Association, Delaware OH VOL 37 NUMBER 9
DELARA Tech: a problem chased down with antennas
Here’s how it starts…a simple thing, seemingly. But this is ham radio… and nothing can be assumed to be simple! THIS is how ham radio works…some suggestions, an Elmer visit for collaboration. Need your help. I have a problem tuning my Chameleon Ecom2 end fed antenna between 7.140 MHz and around 7.25 MHz all of a sudden. It is a multi band antenna which works well for me from 20m thru 80m. But no longer on 40m. The internal tuner on my Yaesu FT-991a begins the tuning process, but as it is clicking through to find proper tuning, the S meter on the rig drops out completely and is therefore unable to tune those frequencies. When attempting to transmit, I get a high SWR warning. And no contacts. There were times yesterday when the antenna would tune on those frequencies. But I cannot anymore. Please share your thoughts. I’m frustrated and am not sure what to do to troubleshoot and correct the issue. Not sure if it’s a failing matching network on the antenna or something with the rig. Thanks for the insight and experience. 73, Jordan W8JJBPrez Joe was right on the case!End-feds have to have a return path, usually the feedline. Check the manufacturer’s documentation or Web site to see what they say about that. Many I’ve heard about have a 9:1 balun so maybe yours is faulty or having some kind of problem. If you changed anything with regard to the feedline or grounding, try double-checking what you did and how it might affect the return path situation. I had a balun, choke actually, go flakey only in cold weather so you might have some moisture issues. But that is only if your end-end uses a balun, which is probably the case.Ed injects a common-sense question- Could be a bad connector, flakey coax, or a coincidence :-) It might be helpful to try a different radio or an analyzer. You don't live too far from me. Send me a private email if you'd like to arrange a time to use my antenna analyzer. I can show you how to use it and then you can troubleshoot. I can take a look at your situation and see if anything else comes to mind. And after some further email suggestions, a visit from Ed resolves the issue! Something we all can remember for future reference. Good afternoon, allThanks to Ed Jones and the experience and insight of the DELARA club, my tuning problem has been solved.After speaking with Ed and the folks at Balun Designs, the problem is the following:Multi band end fed antennas can send a lot of common mode current back along the coax to the radio, especially in frequency ranges which are least resonant. This common mode current confuses tuners, as most have difficulty distinguishing standing wave (SWR) from common mode current. This is especially problematic for internal tuners within transceivers like mine. The result is that the radio cannot tune at those frequencies as long as common mode current is present.The solution: A common mode choke (toroid) to strip the common mode current from the line before entering the radio. https://www.balundesigns.com/model-1115i-single-core-isolation-balun-1-5-54-mhz-5kw/www.balundesigns.comThank you for Ed’s help in coming over and helping the new guy. Thanks to the DELARA membership for your guidance.This willingness to help is what keeps the hobby alive and well, and attracting the new hams. Keep up the great work.73,Jordan W8JJBAnd a further note worth reading from Ed:FWIW, I liked Craig's idea, too, so we first put a dummy load on a short jumper behind the radio to make sure the built-in tuner wasn't malfunctioning and it tuned up. Then we put the dummy load at the end of his coax before the end-fed's matchbox. Still good. So, his radio, feed line, and connectors were good. Then we switched his end-fed matchbox with one of mine. And his built-in ATU tuned up fine. Given the extra weight in my "black box" end-fed transformer, I'm assuming it had more coil and a bit more inductance. But, short of tearing it apart, those matchboxes could just be full of rocks for all I know. We put his end-fed transformer back on and then ran two long counterpoise wires, my theory being too much RF was going down his coax. The counter poise wires just made it worse. I HAVE NO IDEA WHY. I don't know their length so maybe they are the wrong length and some horrible multiple of wavelength. I'm way over my skiis. Anyway, pursuing the common mode theory, we tried one of my isolation/common mode chokes and now his built-in ATU will tune. Since we weren't sure if we were right, I suggested he call the guys at Balun Designs. They're far smarter than me. John Beal W8NX introduced me to them a couple of years ago when I was having problems tuning up a fan dipole. So thanks John!