Why won't my ARRL designed vertical tune on 20?
Displaying 1-7 of 7
| Aug 1st 2020, 06:47 | |
N1AUPTotal Topics: 0 Total Posts: 0 |
I built a vertical antenna that was described in the 13th edition of the ARRL antenna book. It's a 30 foot vertical element, and a 30 foot horizontal element, shaped like an L. 300 ohm twin lead feeds the antenna - one leg of the feedline feeds one element each. That then is connected to the balanced line inputs on an antenna tuner, that then connects to an SWR meter, and a radio. Tuner is a Dentron Supertuner with the balanced line jumper in place. I built one of these in the early 80s, and had good luck with it. I got that design out of 73 Magazine. September 1979 issue. Pages 60 - 62. https://archive.org/details/73-magazine-1979-09 The 73 antenna used 26 foot elements, while the ARRL design used 30 foot lengths. For this iteration, I used 30 feet wire lengths. 14 gauge stranded wire taped to a fiberglass mast. The feedline goes through the air about 8 feet from the ground, and travels down the side of the aluminum sided house, 1 foot from the side. It enters the house through a 4 inch PVC elbow. My antenna will tune below 3:1 on 15, and 10. 20 won't get below 3.2:1, and it's similarly questionable on 40. What did I do? The ARRL article claims the antenna will work on 40 - 10. Any input would be appreciated. Thanks |
| Aug 1st 2020, 13:28 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
You need to experiment with different feedline lengths to find what works best. An antenna analyzer will help. It is hard to predict what will work best when you have wires running close to other stuff. Computer modeling and prediction is a lot more useful when you have the antenna up in the clear, but we don't have that here. Back in the old days rigs often had more matching range. In the old days I had more time to experiment. Zak W1VT ARRL Senior Lab Engineer |
| Aug 2nd 2020, 08:45 | |
N1AUPTotal Topics: 0 Total Posts: 0 |
Your advice makes sense, considering that the feedline is actual radiator, but I did cut off about 20 feet, and it made no significant difference. |
| Aug 2nd 2020, 10:00 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
If you have an antenna analyzer it is possible to use a program like TLdetails to explore optimum feedline lengths. https://ac6la.com/tldetails1.html The program won't take into account feedline radiation but it may be more useful that guessing, though one typically expects 1/4 wave or 1/8 wave changes in feedline length to be significant. And a 1/2 wave length change doesn't do much. A half wavelength just returns you to your starting point--just like going in circles. Zak Lau W1VT ARRL Senior Lab Engineer |
| Aug 3rd 2020, 13:38 | |
N1AUPTotal Topics: 0 Total Posts: 0 |
I have a Rig Expert 600 analyzer, I'll check out the link. Thanks |
| Aug 8th 2020, 09:42 | |
N1AUPTotal Topics: 0 Total Posts: 0 |
Would it be useful to install a Palomar 6:1 balun on the antenna at the radiators, and feed it with 50 ohm coax to eliminate the feedline from the system? I could then play around with the length of the radiators without worrying about the feedline effecting results. https://palomar-engineers.com/antenna-products/baluns-and-ununs/1-8-30-mhz-balunsununs/hf-high-power-balunsununs/61-baluns/ |
| Aug 8th 2020, 11:10 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
That product was intended for antennas that present a 300 ohm resistive load. That antenna was published in a different era, when transmitters had tunable output networks and it wasn't as necessary to have a close match to 50 ohms. Also, many hams were content with an antenna that worked well on just a few bands. There weren't as many bands to cover--just five HF bands. We didn't have 60, 30, 17, 12, and 10 meters. And 160 was shared with Loran. Perhaps you could duplicate the version that worked well for you in the past? Zak Lau W1VT ARRL Senior Lab Engineer |
Displaying 1-7 of 7
