Antenna switch. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Nodes of amateur radio equipment
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Rapid switching of the antenna from receive to transmit and vice versa, when it is necessary to provide half-duplex CW operation, is still a problem in amateur radio. UA3TCH offers antenna switches based on 2A520A diodes with a direct differential resistance of 3,5 ohms, a closed capacitance of less than 1 pF, and a reverse voltage of 800 V (Fig. 1).
Ris.1
When the lamp of the final stage of the transmitter is closed, an active resistance of about 100 ohms is connected to the antenna from the side of the P-circuit (if its quality factor is about 500). It practically does not shunt the receiver input, and therefore there is no need to turn off the P-loop during reception. Moreover, it somewhat improves the selectivity of the receiver, since it has a series resonance below the receive frequency. For example, when operating on the 14 MHz band, it suppresses signals well near the frequency of 12.5 MHz.
The switch diodes are switched with a voltage of -12V when receiving and +250V when transmitting using a simple node on a KT605 transistor (not shown in the diagram).
Diodes 2A520A can be replaced by 2A507A, which, however, have a lower reverse allowable voltage (500 V). In this case, instead of the V2 diode, two 2A507A diodes are connected in series.
Publication: N. Bolshakov, rf.atnn.ru
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