21 Nov Appendix B – NEC User Manual Installation. 4NEC2 is a NEC based antenna modeler and optimizer developed by Arie Voors. This is a 3rd. 22 Aug Hello! Does anyone know where I can find some good tutorial/guide to get a basics of how to use 4nec2. I am total beginner. I was able to find. 14 Sep 4NEC2 is a freeware antenna simulation software program. The guide already shows what the main windows of 4NEC2 do, and shows you If you mean operating instructions, I will redo the manual soon and upload it in a.
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If you have a tall tree, there seems to be little reason to spend too much time burying radials in the lawn! The choke both defines the length of the lower section of radiator, which is the coax cable shield, and also keeps the RF from traveling down the feed line back to the radio. Rasing the antenna higher improves the elevated vertical dipole.
Vertical antenna radiation patterns. Optimizer window shows rapid convergence on correct length L1 to minimize SWR.
For the resonant feed line antenna, the tutoria, is located at the end of the radiating element where the local impedance is very high — voltage maximum and current approaching zero. How much gain will this antenna give me? I just pulled this up in the tree today.
A Simple Pull-up Mono-Band Verticle Dipole Antenna Design – and 4NEC2 Tutorial
Notify me of new comments via email. This simple antenna system is a great sandbox for learning the tricks of the NEC codes and some of the basic principles of antenna design, and to find all the pitfalls of this nice idea.
The gain of elevated antennas is especially better for low radiation angles tutoriao than 15 degrees. If we knew the reactance of the choke we could model it with NEC. To find out more, including how to control cookies, see here: The important thing to do is to define the end of that radiating segment for RF, so there we place a choke. The optimizer is a nice tool, but not magic!
Any choke I made with ferrite was lossy and had a self resonant frequency below my desired operating frequency of 14 MHz. Attempts at direct measurement of capacitance are confounded by parasitic capacitance of scope probes and by resonances with the physical length of coil wires and connections themselves, so that the measured resonances do not reflect the desired stray capacitance of the coil but rather the length of wires.
Antenna Simulation Tutorials using 4nec2
But rather than using another wire, realize that I already have a wire coming back down from the feed point, namely the outside of the co-ax feed itself. Published by Gary Rondeau. I spent an afternoon with a few ferrite cores, some coax cable, signal generator and oscilloscope and can 4nce2 that even good ferrite is not very suitable for this application.
To drive this antenna several questions come up. Much better is just a simple solenoid made from the coax feed line itself. The more inductance the better for these tasks, but we have to build the inductor, either air-core or with ferrite, to hang on the feed line and there will tutoriao capacitance. Choose only one variable at a time to begin with. The numbers I came up with were 24 ft.
The outside of the coax is part of the antenna system itself, and includes the RF choke that defines the lower driven element of the antenna.
Because the choke is so critical, I decided to model several different versions and mis-tunings to see the effects. How can I tune that? If I use 75 ohm coax, how long should the transmission line be?
Should I use 50 ohm or 75 ohm coax? The SWR without additional tuning is around 1. I have tall trees. What about that choke? My gut feeling is that all this effort is misplaced. Reflections from the ends of the cable will tend to cancel each other out with this special length cable. One way to get a handle on this is to compare signal levels against an isotropic antenna.
The optimizer can converge to either solution depending upon starting conditions. View all posts by Gary Rondeau. Vertical dipole tip at 55 feet, green; 75 feet, pink; and 95 feet, tutoiral. You are commenting using your WordPress.
RF current magnitude in green. Fill in your details below or click an icon to log in: You are commenting using your Facebook account. Feedline current with mistuned choke.
Antenna Simulation Tutorials using 4nec2 – KW4FB
Unlike a simple choke on a feed to keep the RF out of the shack, the choke for this application has a much more difficult job to do. A choke near the feed point for a normal dipole is trying to choke off the RF compared to the drive impedance at that point — which may be only a 50 to ohms. By continuing to use this website, you agree to their use. I then run the rest of the feed line down to ground where NEC assumes it is grounded and which could be where the radio is located.