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National
SW-3 Plug In Coils |
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Unlike more
modern radio's which allow you to change bands at the turn of
a single bandswitch, the National SW-3 changes bands by
plugging in a pair of coils.
The operator turns off the radio, lifts the hinged top lid,
and replaces the coils with the desired frequency set.
There are two kinds of coils, a "general coverage" coil which
provides a full dial over a wide frequency range, and the
"bandspread" coil set which provides a full dial over a narrow
frequency range for fine tuning the ham bands.
 Click on the thumbnail
photo to bring up a large picture. The photo above shows the bandspread coil
set with the rf coil on the right and the detector
coil on the left. |
 Click on the thumbnail
photo to bring up a large picture. The above photo shows the general
coverage coil set. The main physical difference
between the general coverage and band spread coils
is that the general
coverage coil set does not have a capacitor and no
wire and plate cap attached to it. |
 Click on the thumbnail
photo to bring up a large picture. The photo above shows a close up of the
unique 6 pin coil bottom. Also shown is the stamped
identification number. |
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SW-3 coils
are identified by
several possible ways. Earlier coils had a colored dot applied
to the bottom of the coil form, in-between the pins. It may or
may not have the coil number stamped on the bottom. Along the
top edge of the coil form, there is an indentation that may
also be colored in. Later coils had a number stamped on
the bottom and may or may not have a colored bottom dot and
the top edge colored in. See the table below for coil
frequency identification. |
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| Range
(Mhz) |
Range
(Meters) |
10-20
Series |
60-70
Series |
30-40
Series |
| General |
Coverage |
1930 |
~1933 |
~1940 |
| 0.09-0.16 |
2000-3000 |
22 |
72 |
42 |
| 0.15-0.22 |
1500-2000 |
21 |
71 |
41 |
| 0.19-0.28 |
1200-1500 |
20 |
70 |
4 |
| 0.25-0.39 |
850-1200 |
19 |
69 |
39 |
| 0.32-0.65 |
500-850 |
18 (purple) |
68 |
38 |
| 0.50-0.90 |
350-550 |
17 (yellow) |
67 |
37 |
| 0.69-1.50 |
200-360 |
16 (orange) |
66 |
36 |
| 1.5-2.7 |
115-200 |
15 (blue) |
65 |
35 |
| 2.5-4.5 |
65-115 |
14 (green) |
64 |
34 |
| 4.2-8.0 |
40-70 |
13 (white) |
63 |
33 |
| 7.0-12.0 |
23-41 |
12 (red) |
62 |
32 |
| 12.0-21.0 |
13.5-25 |
11 (black) |
61 |
31 |
| 19.0-35.0 |
9-15 |
10 (brown) |
60 |
30 |
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| BandSpread |
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| 1.8 |
160 meters |
15A (blue) |
65A |
35A |
| 3.5 |
80 meters |
14A (green) |
64A |
34A |
| 7.0 |
40 meters |
13A (white) |
63A |
33A |
| 14.0 |
20 meters |
11A (black) |
61A |
31A |
| 28.0 |
10 meters |
10A (brown) |
60A |
30A |
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Coil information from an
article by William Fizette K3ZJW, titled "Those National
6-Prong Plug-in Coils" |
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Back to National SW-3
Thrill Box |
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Click on the thumbnail
photo to bring up a large picture. The photo above shows the bandspread coil
set with the rf coil on the right and the detector
coil on the left. 
Click on the thumbnail
photo to bring up a large picture. The above photo shows the general
coverage coil set. The main physical difference
between the general coverage and band spread coils
is that the general
coverage coil set does not have a capacitor and no
wire and plate cap attached to it. 
Click on the thumbnail
photo to bring up a large picture. The photo above shows a close up of the
unique 6 pin coil bottom. Also shown is the stamped
identification number.