ANTENTOP- 01- 2007, # 009

Simple SWL HF- VHF Receiver

From the book "DX Reception" (by Igor Grigorov (RK3ZK), Belgorod, 1994), pp.:76- 81.

(Article published with inessential cutting)

See ANTENTOP- 01- 2007, p.p.: 73- 74.

Using only 4 cheap surplus transistors and 1 mixer SBL- 1 you can do a HF- VHF receiver that provides good reception on HF (12- 29- MHz) and ex- Soviet BC FM VHF- 61- 88 MHz. Receiver catches AM and FM with deviation more the 25 kHz. Such receiver allows very quickly to find a propagation on the spectrum of HF and VHF bands.

The chart of the receiver is shown on Figure 1. Receiver includes balanced mixer (1), low-pass filter (2), high-pass filter (3), VFO that works at 16- 33 MHz (4), superregenerative detector aka IF amplifier on 45 MHz (6). Switched filters are formed a working band of the receiver (HF or VHF). The receiver has two struck points. First lays on 22. 5 MHz the second one is on 65.5 MHz. If you want to have reception on the frequencies just move the IF of the receiver (with help of C11) up or down.

Figure 1. Chart of the simple SWL receiver

Note: The figure is original scan from the "DX Reception" book. English commentary are given inside oval.

The simplicity of design of the receiver and its high sensitivity (just at connection of an antenna in 1 meter length the receiver provides satisfactory reception on the HF and VHF bands) is reached by a superregenerative detector. However the superregenerative detector gives basic lacks of the receiver- low selectivity and low dynamic range. There is no SSB reception. Figure 2 shows the circuit diagram for low-pass (Fig. 2a) and high-pass (Fig. 2b) filters. The filters were made for 50 (75) input/ 50 (75) Ohms output, i.e., the filters require a 50 (75) Ohms antenna and mixer having 50 (75) Ohms input. SBL-1 is okey for that. However the receiver works well with an antenna having almost any input impedance. Figure 3 shows the circuit diagram for the receiver. If you have no SBL- 1 you may do the mixer according to Figure 3.

Figure 2. Circuit diagram for low-pass (Fig. 2a) and high-pass (Fig. 2b) filters

(Values for all capacitors are given in picofarads)

Note: The figure is original scan from the "DX Reception" book. English commentary are given inside oval.

Figure 3. Circuit diagram for simple SWL receiver

Note: The figure is original scan from the "DX Reception" book. English commentary are given inside oval.

Table 1 shows data for inductors of the receiver and filters. All coils are wounded by insulated copper wire in diameter 1-mm (18 -AWG), all coils are air- wounded. The filters are assembled in a box (80X40X40- mm) soldered from two- sided PCB. The receiver is assembled in a box (155x 90x 55- mm), soldered from two- sided PCB. Figure 4 shows component layout for the receiver. The components are sitting on the wiring strips from an old tube receiver. When the receiver will be tuned close the box, where the receiver is assembled, by a plate of a PCB. The plate should be soldered at several places to the box.

Figure 4 Components layout for simple SWL receiver

Design and Tuning

Low-pass and high-pass filter made strictly to Table 1 and Figure 4 does not require any tuning.

VFO made from good parts according to the schematic works straight away. Only the tuning is the set up of the frequencies range. Needed frequencies range do rough by the pressing- stretching of the L9, fine with the C2. Arrange L10 near L9 to maxima and equal across the band sensitivity.

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