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E-enthusiasts in the entry-study phase, and ultimately, the total electronic small production, small repair activities to enhance their practical ability. Assembly of a radio or radio repair the vast majority of beginners are bound to be one of the activities, this article on the importance of radio devices - magnetic antenna and IF transformers to analyze. First, magnetic antenna
     Magnetic antenna are in a bar at around the two groups are not connected to each other coil, the role of space are receiving electromagnetic waves. Magnetic antenna has a good direction, making the radio rotation in a certain direction when the loudest voices, but also reduces the noise.
     Transistor radios in the assembly process, can be made magnetic antenna.
     1. Magnetic antenna of the Q value and bar material and the use of frequency-related. To receive AM signals using Mn-Zn ferrite bar; receiving short wave signals using nickel-zinc ferrite bar. For the same diameter or cross section of the bar, preference should be given the length of the longest in order to improve radio sensitivity.
     2. The Q value of magnetic antenna coil windings by the impact of different positions with more obvious. We can see from the experiment: the coil in the best position on the bar are the length of the coil windings Center and the bar length of the mid-point distance of 1 / 5 ~ 1 / 3, when the movement of coil inductance with the larger changes in direction or.
     3. Bar of the current flowing through the coil are relatively high frequency. As the high-frequency current with the skin effect, the conductor of the high-frequency currents are presented as the current frequency of resistance increases, the results of wire on the high-frequency signal power loss will increase. To overcome this, in the medium wave range, magnetic antenna coil usually consider increasing conductor cross-sectional area, which adopts the diameter ∮ 0.1Mm for 7 shares of the enameled wire winding; short-wave primary coil magnetic antenna often used ∮ 1 ~ 1. 5mm between the silver-plated copper wire around, turn to turn away from the general to 2 ~ 3mm.
4. Due to the high impedance tuning circuit, transistor input impedance of low impedance matching problem to consider, so that the largest signal output. L1 and L2 around 10:1 Turns Ratio general, L1 is usually 60 ~ 80-turn.
     5. Magnetic antenna device, should be far away from the magnetic field (such as speakers, transformers, etc.). Application of non-metallic stent materials. Bar easy to fracture, the use of the course have to pay attention to.
     Second, IF transformer
     Intermediate frequency transformer (commonly known as in weeks), are superheterodyne transistor radio in a unique fixed-resonant transformer circuit, but the resonant circuit can be fine-tuned in a certain range, so that access can achieve the stability of the circuit resonant frequency ( 465kHz). With fine-tuning the relative positions of core changes to complete.
     Radio IF transformers are single-tuner-style, structure, relatively simple, occupy less space. As the transistor input, low output impedance, in order to enable the IF transformer with the transistor input and output impedance matching, has tapped primary, and has a few little sub-loop coupling coil. Dual-tuner type of advantage is a better selectivity and a wide pass band, used in many high-performance radio.
     Transistor radios are usually two-stage IF amplifier, so necessary in the three weeks before and after the class coupled with the transmission of signals. The actual circuit used in the weeks BZ1, BZ2, BZ3 symbol. In use can not change their position in the circuit.
     Oscillation coil (MW) of the week is similar in shape and it and the corresponding components of the composition of the transistor radio frequency level. The use of isovolumic double (270pF × 2), at the same time regulating the importation of tuned circuit resonant frequency and the local oscillation circuit of the vibration frequency to ensure that the scope of the entire receiver band are: f vibration-f letter = 465kHz. Commonly used models for the LTF-2-1 (the initial 144 +8.5 Turn, Turn sub-11.5) and LTF-2-3 (the initial 4.5 +82 orbicularis, sub-orbicularis 8).
     Finally to mention that: tuner should be without a sense of change as far as possible, using a knife tuner. Adjust each frequency oscillation transformer or coil magnetic cap range not too large, hard to pay attention to Antimagnetic cap rupture.

The article translation from:磁性天线与中频变压器