The only way I can get away with that in the presence of the ever-present 60 Hz fields is to couple the antenna to the jfet gate with a small capacitance. I placed a 2 megOhm bias resistor from gate to common at the input to a 2N3819 jfet and rely on that 2N3819 RF stage input impedance to be high enough compared to the antenna impedance that I can ignore antenna length over the tuning range of the receiver. I know from my reading that the maximum impedance the antenna will present to the receiver is about 2,000 Ohms. The RF stage immediately following the antenna has an input impedance high enough so that the signal voltage on the antenna is essentially transferred to the gate of the first stage over the tuning range of the receiver without antenna tuning. I have borrowed a concept from bioinstrumentation: I treat a short wire antenna as an electrode rather than an antenna. Oscillation is very noisy, but reception without oscillation is good. This receiver is suited for reception of AM signals with the regenerative stage not oscillating. I have attempted to incorporate every improvement I have thought of into this receiver, including maximum mechanical rigidity and electrical shielding. This web page describes a small, single tuned circuit regenerative receiver primarily for daylight reception in the 16, 19, 22 and 25 meter international shortwave broadcast bands.
0 kommentar(er)
