Receiving Antennas for LW and MW Band

Receiving Antennas for LW and MW Band

Amateur radio already has got LW bands- it is 2200- m (136- kHz) and 630- m (473- kHz). These interesting bands need not only transmitting but receiving antennas. The article is described several designs of receiving antennas for LW band.

At first I would like to introduce old but very useful article in Radio- Electronics magazine. It was published in the issue of June 1983 and described very interesting variant of the loop antenna for VLF- LF. It was article Loop Antennas for VLF- LF: R.W. Burhans, pp/: 83- 87, the full article you may found at https://archive.org/details/radio_electronics_1983-06/mode/2up

Inside of the article it was part that described very interesting design of the receiving loop antenna made on a ferrite rod. The quota from the article described the ferrite loop antenna is below.

Balanced Loops

As discussed previously, to obtain the best null performance, loop antennas should be operate so that the capacitance between the antenna and electrostatic shield is the same at all points along the loop. With single winding that's a problem, since one end of the winding has to be grounded in some way. A loop with a center- tapped winding is often used together with a preamp with a balanced input, but there is a better way of winding loops on long ferrite- rods that also reduces the inductance of the whole winding and result in a single- ended terminal for the loop.

The technique, developed by the U.S. Army Signal Corps many years ago, involves right- hand- and left- hand- sense windings starting at the center of the core. The resulting loop, shown in Fig.9, still has opposite- phase nulls of opposite ends, but now has excellent electrostatic symmetry with respect to the trough shield. The sensitivity of this coil the same as that of a coil wound in a single direction from one end to the other, but the inductance is reduced, resulting in a higher self- resonant frequency. The termination point in the center of the core practically eliminates induction- field noise- pickup, even with a single- ended preamplifier system.

Radio- Electronics

June- 1983

When winding a coil with a relatively large number of turns, it is advisable to check the winding for inductive balance because the ferrite core material may not be uniform from end to end. Another factor contributing to non-uniformity is that it is difficult to wind a perfectly spaced coil by hand. That is why the figures indicating the number of turns on each side described in Table 1 are different.

To tune the balanced- loop coil arrangement shown in Fig. 9 to resonant at 60- kHz, a fixed capacitor to about 500 pF can be placed in parallel with a small variable capacitor of up to 350 pF (and the 330- pF distributed capacitance of the coils).

Ferrite rod antennas, almost similar to described above, were tested by the Russian amateurs. Results were pasted at forum at radioscanner.ru. I would like stopped by several designs of the antenna.

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