1. Inserting the loading midway on 40 each side of the span, which requires two additional insulators. 2. Inserting the loading at the center, supported by the antenna wires. After modeling with NEC-2, and later with NEC-4, I could see very little dif-ference between these two methods. What follows is the description of an antenna which may allow to obtain good performances even in limited space, the antenna which I'm about to describe is a "linearl loaded dipole" (LLD) which some call the "cobra" antenna due to the "snaking" of its wires
40m LinearLoaded Dipole Resource Detail The
Here are the other videos in my Linear Loading journey: 1. Shortening a 40 meter quarter wave vertical: https://www.youtube.com/watch?v=cmqEa. 2. Shortening a 10 metre dipole using linear loading: https://www.youtube.com/watch?v=Dcdk4. 3. Short 40m dipole for a small garden: https://www.youtube.com/watch?v=AO9Xj. 4. Introduction Feed (A) f/f 0 = 1.0, R = 72 Ω Feed (B) f/f 0 = 0.67-0.70, R = 35 Ω Feed (C) f/f 0 = 0.55-0.60, R = 26 Ω Loading coils can be used to shorten a dipole. Another method is called Linear Loading. With Linear Loading, the dipole elements are effectively folded back on themselves, 2 or 3 times, as shown in the drawing on the right. 1 I've recently learned about linear loaded dipoles as one way of building a physically shortened antenna. As I understand it, any shortened antenna will have reduced bandwidth and linear-loaded dipoles suffer from this as well. The DX Engineering Linear-Loaded Multi-Band Dipole (Patent Pending) is a 74 ft, lightweight yet rugged design that is usable with a tuner from 3.5 to 30 MHz. It's ideal for portable or tactical use and can be easily installed in attics, small lots or Covenant Condition Restricted locations. Features
Linear loaded short dipole Klaus & Lita
Finally I decided for a linear loaded dipole; the layout and resulting dimensions are shown below. First measurements at the resonance frequency showed a low input impedance at the dipole's feed point with values around 10 Ohm. Design of a Two-band Loaded Dipole Antenna Calculate the LC trap values given the physical size of the antenna and two desired resonant frequencies. wanted to put up a dipole antenna in my attic but didn't have space for a full sized 40 meter antenna. A linearly loaded dipole, as illustrated below.. is about 30-35% shorter than a "classic half-wave dipole" at the same frequency of resonance!. has a radiation resistance around 35 Ohms. (You will need an impedance matching tuner at the other end of the coax!). just as effective as a "full length" half-wave dipole! :-) The method of "linear-loading" is a fancy way of saying "fold back on itself" - It reduces the overall length of an antenna without resorting to loading-coils. The performance is still good, so ideal if you have a small garden or want to try experimenting with bits of wire.
Small Cheap Linear Loaded 80m Dipole YouTube
Small Cheap Linear Loaded 80m Dipole Watch on If you can't fit a full-size 80 meter dipole antenna into your small urban lot, then this modified linear loaded design from Callum (M0MCX) may be what you need. Callum takes us through the design, construction, and testing phase of this shortened dipole. The 40 meter half-wave dipole antenna, intended for NVIS duty, described in the schematic diagram above, is made portable for field work by using linear-loading technique which will yield an antenna span about 33% shorter than normal!
Linear Loading using 450 ohm ladder-line to see if a shortened dipole could provide a tune on 10 metres. It says that linear loading is a "little understood" alternative to inductive loading that can be applied to almost any type of antenna. Furthermore, "…it introduces very little loos, does not degrade directivity patterns, and has low enough Q to allow reasonably good bandwidths."
Linear Loaded Dipole for 20 m Klaus & Lita
Linear loads do not model accurately using the TL facility of NEC. There are two major factors (and a number of minor ones) that contribute to the inaccuracy. First, the currents on the wires of the linear load are rarely, if ever, exactly equal in magnitude and opposite in phase. Here is my dipole for 40m band. It is a simple linear loaded dipole feeded with 450-Ohm openwire feedline. I designed it for resonance at 7.050 MHz, but using my LDG AT 100-PRO-II tuner I can tune it also on 30m and 80m bands. The latter with poor results. I use to simulate all my antennas with MMANA-GAL.
