Progressive Receiver Design - Tuned Circuit Data
Freq. Low
Freq. High
C1
pF
pF
C2
pF
pF
C3
pF
pF
C4
pF
pF
C5
pF
pF
C6
pF
pF
C7
pF
pF
C8
pF
pF
L1
uH
uH
T1
uH
uH
T2
uH
uH
0.45Mhz *
0.46MHz
10-100
100
2200
6800
6800
82
1.8
2.0(a)
10-100
10
470
1500
1500
20
1.8
2.0(b)
5-50
10
270
820
820
35
3.5
3.8
5-50
47
270
470
470
8.5
7.0
7.1
5-10
33
100
330
330
4.5
9.0 *
9-10
22
100
330
330
3.3
10.0
10.15
5-10
22
82
220
220
2.9
14.0
14.35
5-10
18
68
220
220
1.83
18.06
18.17
5-10
18
47
180
180
1.3
21.0
21.45
5-10
18
47
180
180
1.0
24.89
24.99
5-6
15
33
150
150
0.90
28.0
29.7
5-11
12
33
100
100
0.71
50.0
52.0
5-9
10
22
100
100
0.30
Notes:
Suggested winding details are shown below.
The inductance values for T1 and T2 are for the tuned winding.
All frequencies in MHz unless otherwise stated.
Capacitor C1 is shown in the form minimum value - maximum value.
The values shown for 450-460KHz and 9MHz are suggested values when the NE602 is used as a product detector in a superhet receiver. Constructors might like to try ceramic resonators instead of conventional tuned circuits on these frequencies.
Coil Assemblies:
If constructors wish to wind their own inductors and transformers there are a variety of new and second hand coil assemblies available from the amateur radio market. The most common types are in ½ inch square aluminium cans, approximately ¾ inch high which are available from rallies and surplus suppliers in the form of assembled PC boards out of mobile radio equipment. Half inch diameter iron dust toroids may be used but will require tuning with trimmer capacitors and only limited details have been provided.
Finished coil assemblies should be tested and then the windings varnished and left to dry for at least 24 hours - clear polyurethane varnish is suitable for this purpose. To retain the adjustable core a small amount of silicon tap grease may be put into the former thread prior to assembly - do not use a grease that contains any metallic or conductive compounds.
Transformers T1 and T2 should have a turns ratio of between 8:1 and 10:1 between the tuned winding and the coupling link - the coupling link is wound over the cold or earthy end of the tuned winding. The tuned winding is connected to the tuning capacitor C6 or C8 and the coupling link to the aerial or receiver circuit.
Transformers T1 and T2 form a bandpass filter, slightly overcoupled on some bands in order to cover the whole of each band without retuning.
The following table gives coil details (Toko part numbers where available from one or more UK suppliers) and suggested winding details for use with the ½ inch square assembly - capacitor values as shown on the first page:
Frequency Range
L1
T1
T2
450-460KHz
68t, 7/48# Litz wire plus a pot core
1.8-2.0MHz (a)
65t, 7/48# Litz wire
1.8-2.0MHz (b)
79t, 7/48# Litz wire
3.5-3.8MHz
40t, 7/48# Litz wire
7.0-7.1MHz
23t, 36# wire
9.0MHz
27t, 36# wire
10.0-10.15MHz
KANK 3335
23t, 36# wire
23t, 36# wire
KANK 3335
KANK 3335
14.0-14.35MHz
17t, 30# wire
18.06-18.17MHz
14t, 30# wire
21.0-21.45MHz
12t, 30# wire
24.89-24.99MHz
12t, 30# wire
28.0-29.7MHz
11t, 30# wire
50-52MHz
7t, 26# wire
Winding wire should be solderable-enamel covered copper wire. The 7/48# Litz wire is seven strands of 48# enamelled wire with an outer covering of cotton and gives a higher Q value than single strand wire. If Litz wire is not available use 40# (swg) single strand wire.
Each winding should be close-wound and take up no more than two thirds of the former length. If more space is required then the winding should be scramble wound back and forth over itself until the required number of turns has been achieved.
Make each winding off to the base pins by pre-tinning the wire before threading it into each pin and soldering in place. Test each coil before applying any varnish.
Additional oscillator coil information has been provided by project participants as follows (frequencies in MHz):
Freq. Low
Freq. High
C1 pF
C2 pF
C3 pF
C4 pF
C5 pF
L1 uH
6.97MHz
7.105MHz
8-30
330
110
390
390
13t, 26swg, enamelled copper wire on T50-6 toroid
13.6
14.4
8-30
39
56
220
220
KANK3335 1.5uH
13.95
14.5
8-30
110
56
220
220
KANK3335 1.5uH
16.8
19.5
8-30
0
56
220
220
KANK3335 1.5uH
