The amateur bands are as follows: 1.8-2.0MHz (160 metres), 3.5-3.8MHz (80 metres), 7.0-7.1MHz (40 metres), 14.0-14.35MHz (20 metres), 21.0-21.45MHz (15 metres), 28.0-29.7MHz (10 metres). Outside Great Britain some of these frequencies are extended.
In Figure 11, a 2-pole 6-way switch selects the required coils, for 160, 80, 40m and other bands. Signal input is to gate 1. The potentiometer VR1 provides a gain control, to avoid over-loading of the receiver with strong signals. Drain and source circuits are arranged as in Figure 7, with capacitor coupling to the receiver. If the drain circuit were also tuned, twelve coils would become necessary, with ganged tuning.
Winding of the six aerial coils is not too critical, as it is only necessary to set the cores so that amateur signals throughout each band can be peaked by VC1. All coils are wound on formers approximately 9/32in or 7 mm in diameter, and 1in long.
- 10m. Seven turns 26swg side by side. Aerial coupling four turns.
- 15m. Nine turns 26swg side by side. Aerial coupling five turns
- 20m. Fifteen turns 32swg side by side. Aerial coupling eight turns.
- 40m. Twenty eight turns 32swg side by side. Aerial coupling fifteen turns.
- 80m. Sixty turns 34swg side by side with two cores. Aerial coupling thirty five turns.
- 160m. 120 turns in compact pile occupying ¼in width, 34swg. Aerial coupling 60 turns in pile.
Layout should place the switch near VC1 and G1, and should permit very short connections for 10m, 15m and 20m coils in particular.
In view of the number of turns required for 160m, it may be noted that a receiver type medium wave band coil can often be used here. Some coils of this type will reach 160m with the core screwed fairly well out. If not, some turns need to be removed. A Litz wound coil here will give some improvement in efficiency.