This article describes how to construct a loop from ribbon cable. I looked around for lightweight materials from which to construct a loop. They also have to be non-metallic, which limits the selection quite a bit. Some discarded vertical blinds offered me the answer. The vertical blind slats are about 84 inches long and 3 1/2 inches wide, and have a slight curve. Individually, they are much too weak to work as a support, but the slight curvature can be used to create a fairly strong support structure.
The Folding Loop Antenna
The end result is a odd looking contraption when folded, 54 inches long, about 11 inches wide half of its length, and 5 1/2 inches wide for the other half. It has droopy wire hanging on it, and has a tuning capacitor sticking out. It is long enough to be slightly inconvenient, and heavy enough to be slightly annoying - but the weight can be reduced by changing the thickness of the wood, 1/4 inch plywood, perhaps.
You are sure to get a few stares walking into a public area such as a pool with this contraption, but as long as you re-assure anxious lifeguards that you have no intention of taking it into the water as a "surf board", you should be fine!
If the receiver has a ferrite bar antenna, there are two methods of coupling. One is to wrap a few turns of wire around the ferrite bar at the end opposite the existing windings, and couple those windings to the coax. The other is to simply get the radio close to the loop.
ON7YD Vertical antenna with inductive toploading
In an environment with a lot of 'vertical objects' (trees etc.) close to the antenna inductive toploading can significantly increase the performance of a short vertical antenna. The antenna is 14m high at the right end (where the loading coil is) and 16m high at the left end. The horizontal top section is 22m long and consists of 4 parallel wires, each 90cm separated.
AM loop anennas
An AM loop antenna is one of the true marvels of electronics. Requiring no power, it takes advantage of the resonant properties of an inductor and a capacitor connected in parallel to receive weak AM stations. The "loop" part of the antenna is the inductor, and the tuning capacitor makes it resonate at a desired frequency.
As a boy in Abilene in 1967, I discovered the basic principle of the loop antenna. By removing a relatively small spiral loop in my five tube table radio, and substituting a much larger loop salvaged from an older radio, I could receive my favorite station - KLIF from Dallas better. I hid the loop in a cardboard holder featuring the logo of a favorite rock band, and enjoyed many hours of good listening. Lacking the mathematical background to understand antenna theory - I could not take the concept to the next phase: designing my own loop. Nevertheless, the spiral loop - combined with the antenna section of the radio's tuning capacitor - formed a very good loop antenna. I understood quite well that the bigger the loop, the more stations I could receive.
DK5PT's compact ferrite loading coil for LW antennas
The air-gap Variometer. What I am using for LF antenna matching is a relatively small ferrite pot-core instead of big coupled air coils. Pot cores are primarily used for power transformers in switching supplies, not usually for high Q coil applications. The core is a SIEMENS PM74/59 with 74mm diameter. The ferrite is N27.
A 10 foot receiving loop for LF DX
Basically the loop is like most antennas, just a big resonant tuned circuit probe that is coupling into the radio signal's electromagnetic field. The 1-turn link couples signals out of the main loop to be fed to the receiver. The loop is tuned (signals peaked) with the variable tuning capacitor.
The frequency tuning range of the loop basically depends on the number of turns in the main coil and the size of the tuning capacitor. My ten-foot loop has 14 turns of #20 plastic coated stranded copper wire. The tuning capacitor is a 400pf dual variable with both sections connected in parallel. The tuning range of the loop is from 180kHz to 410kHz approximately.
The "Lazy" Loop by Jim Moritz
The great advantage of this sytem is that the critical tuning components are nice and dry in the shack, no remote control, no waterproofing, just twiddle and go!
The Four Foot Loop Antenna
Detailed construction details. The large loop allows many distant stations to be heard on even a modest receiver. As expected, receivers have personalities, related to the number of IF stages, the presence or absence of a tuned RF stage, and particularly the AGC characteristics.
Experiments with a Top-loaded Vertical Aerial for LF
Alan Melia G3NYK and Finbar O’Connor EI0CF
Finbar did some experimenting very early with a novel form of Top-loaded aerial for LF. This was stimulated by a short piece in Pat Hawker’s Technical Topics column in the RSGB Radcom in November 1974 [3], and revisited in May 1988. The original write-up carried the source references to an IEEE Transactions paper [1]on LF and VLF, and a Canadian Broadcasting Corporation Engineering Review [2] with some practical details of an MF BC aerial tests. The construction seemed quite simple, and Finbar experimented for a while before the UK gained access to 136Khz. After our sucessful measurements with the simple ground loss bridge, Finbar was keen to see if the aerial could be developed into a form suitable for small gardens as a way of encouraging some more activity.
The Umbrella Loop
I saw the answer in an everyday object that just about everybody owns - an umbrella. Like my "ideal" loop, it needs to have a large deployed shape, yet needs to be lightweight enough to carry, and needs to fold to a compact form that is easy to store. It needs to deploy quickly. It has many characteristics in common with what I want for loop! But - could I make a loop antenna based on the umbrella design? I cannot use umbrella hardware directly, because it is metal. But - I found a way to use wood instead of metal for the supports, and a minimum of metal used near the center of the mechanism.
