Fast switching antenna from reception to transmission and Vice versa when it is necessary to ensure half-duplex operation Telegraph, remains a problem in Amateur radio. UA3TCH offers antenna switches to perform the diodes AA having a direct differential resistance of 3.5 Ohms, capacitance in the closed state is less than 1 pF and reverse voltage 800 V (Fig. 1).
Fig.1
When the lamp terminal of the cascade of the transmitter is closed, to the antenna from the P-loop (if its q-factor of about 100) is connected to the active resistance of about 500 Ohms. It practically bypasses the receiver input, and therefore, during the reception, there is no need to disable the P-loop. Moreover, it improves the selectivity of the receiver, as it has a serial resonance below a frequency of reception. For example, when working on the 14 MHz band it is well suppresses the signals near the frequency of 12.5 MHz.
The diodes switch commute voltage of-12V and +250 V when transmitting using a simple knot on the transistor QT (not shown).
Diodes AA can be replaced by AA, having, however, a lower reverse voltage (500 V). In this case, instead of the diode V2 is consistently include two diodes AA.
Publication: N. Bolshakov, rf.atnn.ru