DIY RF modules. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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DIY RF modules. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Data transfer

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Sometimes a situation arises when SAW resonators are available for those frequencies for which the industry does not produce receiving modules. And it's no secret that the cost of industrial microassemblies of about 7 ye (RX 5000) can discourage anyone from experimenting.

The modern element base allows you to assemble both the transmitter and the receiver on your own with characteristics that are at least as good as those of industrial modules.

(click to enlarge)

Data transmitter

A standard circuit tested by many radio amateurs.

It consists of a controlled master oscillator and a power amplifier.

Power is about 10 mW, current consumption is 15 mA. The master oscillator current is about 2 mA. The current consumption and power of the final stage can be adjusted by bias resistors. It should be remembered at the same time that the current of the final stage over 50 mA can disable the transistor used in this design.

(click to enlarge)

Data receiver

The receiver is a super-regenerator with a sensitivity of about 1 μV. Retains performance from 3 to 6 volts, while not "leaving" the frequency.

The connection of the super-regenerator with the antenna is inductive, which makes it possible to avoid the detrimental effect of pickups and strong signals on the operation of the super-regenerative cascade.

The receiver is tuned by shifting and expanding the turns of the coil in the collector circuit. The use of capacitors in parallel with the collector coil is undesirable because it worsens the quality factor of the circuit.

At a frequency of 423,2 MHz, the circuit has 9 turns.

In numerous tests carried out, it turned out that the use of UHF in conjunction with a properly tuned receiver of a similar type does not give anything in terms of improving sensitivity, but only worsening the dynamics of the super-regenerator allows for some negligence in its tuning.

The AM signal received by the receiver has a very small amplitude, so it is first amplified and then fed to the input of a comparator (threshold device).

A log 1 appears at the output of the comparator if the voltage level at its input exceeds a certain level.

In the process of setting up the receiver, the signal emitted by the transmitter is conveniently controlled even in analog form after the first amplifier (terminal 1 of the LM 358), by connecting the input of a conventional ULF there.

DIY RF modules

Download PCB layout files in lay format

Author: Sergey, Kremenchug; Publication: cxem.net

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