I had made a modified inverted V 40 m antenna recently with highest point about 1 m to one side of the feed point. This was made so just to suit the space constraints in my location. Highest point was attained using a 6 m GI pipe on to which a nylon rope was attached to host the antenna. Another 3 m of CPVC hot water pipe was used to elevate the region of the feed point away from the first floor fence. I had used two lengths of 10 m HLF 200 coaxial cable with PL 259 connectors at both ends as the feedline. The two cables were joined together using an SO 239 barrel connector. Surplus cable was placed in U pattern on the terrace, almost at right angles to the antenna orientation. The initial SWR was 1.6:1 at the lower end of the band and 2.7:1 at the upper end of the band. Wanted to see if making the surplus cable into a coil would change the SWR.
Maybe if the exam was more than A B C D - people would already know the answer. You cannot tune a antenna by changing coax length, all you do is trick the meter. If you were going to check resonance - you would use a antenna analyzer with a piece of coax 1/2 of a wavelength - electrically long.
I am using a 20 m long HLF 200 cable for my 40 m modified inverted V dipole antenna. But it is two 10 m lengths joined by an SO 239 barrel connector. NanoVNA is definitely there on my wish list. Waiting a bit as I have already spend a bit on a new radio, cables etc. RigExpert is a bit too expensive and more difficult to procure in this region Jerry. 73 de Jon, VU2JO
The OP is from India. Do you know what their license tests are? WRONG. It's true that you cannot "tune" an antenna by changing the coax length. But there are cases where you CAN change the SWR at the shack end of the line by changing the coax length. Here's a simple example - try to follow along: Suppose you put up an HF antenna, trim it to resonance, and the feedpoint impedance turns out to be about 110 ohms, resistive. And suppose your radios in the shack are designed for 50 ohm loads. If you just run 50 ohm coax from the antenna to the shack, and the coax has low loss, the SWR at the shack end of the coax will be about 2:1 or worse. BUT If you run 75 ohm coax from the antenna to the shack, and adjust the length of the coax to be an odd number of electrical quarter-wavelengths long (meaning you include the velocity factor in the length calculation), the SWR at the shack end of the coax will be close to 1:1. You can also use an electrical quarter-wavelength matching section of 75 ohm coax from the antenna, and then 50 ohm coax to the shack, and the SWR at the shack end of the coax will be close to 1:1. This sort of thing doesn't "trick the meter". It's a valid way of achieving an impedance match. The main problem is that it's frequency sensitive. Yes, that will work with an antenna analyzer, noise bridge, etc. Think about why the coax has to be 1/2 electrical wavelengths long. Also, note that any multiple of 1/2 wavelength can be used. And now a question for you: How does one check that a piece of coax is an electrical 1/2 wavelength long?
Several hundred feet of RG-174 will make any antenna look flat... esp. at VHF. N2EY mentions using coax as an impedance converter, that trick is what makes the magic in the G5RV system. My W5DXP dipole for 40/30 meters (he did the math for me as a favor, sure miss his presence on the forums) uses twinlead to get a very close match for both bands. Both dipole and twinlead length, base on velocity factor, were close... but some fine pruning of the twinlead was needed to get the best compromise for both bands. A remote MFJ 1kW tuner handles the minor corrections.
You are right. When I wrote my Advanced Grade ASOC Exam in 1988, it was full questions and not A,B,C,D multiple choice questions. As I was was upgrading from Grade I, I did not have to take the Morse Code test again. I think it is MCQ now-a-days from some of the model questions I have seen online. But I have not checked with anyone who has appeared for the exam recently. We do not have 4 classes of licenses now. Only Restricted and General. General Class still needs Morse Code. Exams are conducted by Ministry of Telecom through Wireless Monitoring Centers. We do not have the scheme of Volunteer Examiners. 73 de Jon, VU2JO.
