Extremely important factor for good work of simple radio receivers is the outside antenna that has to be long enough, and in which voltages induced by the radio transmitters will be high enough. At first sight, one can think of using instead some modest antenna made of a piece of wire, compensating that with supplying the receiver with amplifier strong enough to give the end result as if much better antenna have been used. That, of course, is not the case, since every amplifier creates noise that makes the reception worse, if not impossible. This fact is the cause for a radio-amateur saying that "Antenna is the best HF amplifier." The external (outside) antenna is being made of copper wire, thick enough to resist strong wind conditions. In the sense of mechanical strength, the best thing is to use the litz wire (cable), i.e. a cable made of huge number of thin threaded copper wires. There is no need to remove the wire isolation if it exists since it doesn't represent an obstacle for the electromagnetic waves. The length of antenna is being determined in accordance with the "TLTB" law (The Longer, The Better ). The antenna that we have been using for testing the receivers described herein was 6 metres long (the length of the Radio Receivers Lab at "Tesla" highschool, where it was spread), but if you are in position, you should make it even longer (the author has a friend whose antenna is about 30 metres long). It should be moved away from the sources of electrical disturbances (public electricity cables, various household electrical devices, cars, electric motors etc.). Considering this, the best place for your antenna should be the building roof. The wire can be crossed between two chimneys (Pic.3.3), between a chimney and some pillar, between two purposefully built pillars, between two buildings, a building and a pole in the yard etc. You should, however, always keep in mind that the wire, however strong it may be, can snap during some big storm and, in case that happens, underNO CIRCUMSTANCES it should fall onto electrical network cables, telephone leads and similar, or to cause some other damage. if your roof cover is not covered with tin, the attic could also be a good place for the antenna. You can also stretch it between two stronger laths attached to two opposite window frames of your apartment. If you have no other options, you can put your antenna between the walls in your room.The antenna must be electrically isolated from the carriers being attached to. In amateur conditions, one can make the isolators of a piece of thick wall plastic pipe where, acc. to Pic.3.3, an indent should be made with the round rasp, in order for the wire not to slip away. The antenna lead is another piece of wire which carries the signals from antenna into the receiver. It should be isolated and placed in such a way not to touch the walls, to be as far from metal parts as possible (gutters, city grounding etc.).At the end of this chapter, let's just say that in mobile receivers ferrite antennas are being used, which we are going to talk about later.
NO CIRCUMSTANCES it should fall onto electrical network cables, telephone leads and similar, or to cause some other damage. if your roof cover is not covered with tin, the attic could also be a good place for the antenna. You can also stretch it between two stronger laths attached to two opposite window frames of your apartment. If you have no other options, you can put your antenna between the walls in your room.
The antenna must be electrically isolated from the carriers being attached to. In amateur conditions, one can make the isolators of a piece of thick wall plastic pipe where, acc. to Pic.3.3, an indent should be made with the round rasp, in order for the wire not to slip away.
The antenna lead is another piece of wire which carries the signals from antenna into the receiver. It should be isolated and placed in such a way not to touch the walls, to be as far from metal parts as possible (gutters, city grounding etc.).
At the end of this chapter, let's just say that in mobile receivers ferrite antennas are being used, which we are going to talk about later.
