Radio microphone 88...108 MHz. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment
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I propose a diagram of a simple radio microphone. Unfortunately, I do not know its author, because I got it from my friend, he also received it. During testing, the scheme showed good repeatability, not critical to the type of parts used.
(click to enlarge)
The scheme is quite economical (when used as a battery from a wristwatch as a battery, it works for a day). Despite the fact that the circuit is not "quartz", the frequency stability is quite high. The use of the L3 coil made it possible to reduce the length of the antenna to 30 cm.
Tuning to a frequency of 88 ... 108 MHz is carried out by coils L1 and L2.
L1 contains 8 turns of PEV wire Ø 0,3 mm on a mandrel Ø 2,5 mm. L2 and L3 differ from L1 only in the number of turns. For L2 it is 6, and for L3 it is 15 turns. In some cases, C7 can be excluded. BM1-MK3-3, VT1 - KT368. Good results were shown by the M1-62 microphone.
With some design experience, you can create very miniature radio microphones. I managed to make a radio microphone according to this scheme on a 1x2 cm board (without a microphone).
Author: A. Podobed, Minsk
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| Random news from the Archive Finder Series 72 Liquid Level Control Switch
01.10.2015
Level control switches are mainly used to turn the pump on / off when the liquid reaches a predetermined level or to prevent leakage. Such relays are used in automatic control systems for filling / draining liquid in tanks - in wells, in sewers, in chemical reactors.
Model 72.11 has a fixed sensitivity (150 kOhm) and a time delay (1 second), in model 72.01 (for example 720180240000 for 24 V DC, 720182400000 for 220 V AC) they can be changed (5...150 kOhm, 0,5/7 seconds). At the same time, the same relay can be used for both filling and draining. The work of the 72nd series is based on the principle of "positive logic". Using two electrodes, it is possible to determine the level relative to one electrode - above / below. By adding a third electrode, you can control three levels - above / within / below.
The relay is used with liquids with sufficient resistivity - tap water, spring water, rain water, sea water, waste water, liquids with a small amount of alcohol, milk, liquid fertilizers.
Positive logic provides additional security. If the relay fails or the control voltage is interrupted, the relay will automatically open the contacts. This will prevent overfilling or running the pumps dry.
Turning on/off the pump when approaching the lower/upper level is controlled by the delay value. Decreasing it provides more precise level control, but increases the frequency of pump operation. The shutter speed should be set based on the volume of the tank and the rate of its filling / drainage.
The durability of the electrodes depends on the distance between them. The larger it is, the less often the switching of contacts will occur and, which will increase the lines of the contact service.
Single-phase electric motors of small power (up to 0,55 kW) can be connected directly to the relay circuit. If frequent switching on / off of the motor is expected, an intermediate relay or contactor must be used. In powerful motors, you need to use a contactor. The maximum distance between the electrode and the relay is 200 m.
As an electrode, it is recommended to use a float switch of the 72A1 series (for technical water supply) or 72B1 (for dirty water).
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