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Why You Should Have a Wavemeter
485
A PERFECT WAVETRAP
IN ADDITION to using the wavemeter of Fig. i as illustrated, the instrument may be used as a wavetrap for the elimination of an interfering station. A wavetrap consists of a combination of inductance or inductances and capacities so arranged that the combination opposes the passage of any given frequency. To use the wavemeter shown in Fig. i as a wavetrap connect it as shown in Fig. 8 and in Fig. 9. Fig. 8 shows the connection to be made in the case of a receiver connected to an antenna. Fig. 9 shows the connection where a loop receiver is used. The operation in either case is the same. Set the condenser of the wavemeter at maximum capacity and tune the receiver in the regular manner. When the desired station is received and interference is present vary the condenser of the wavemeter and readjust the receiver. A setting will be obtained where the interference will be entirely eliminated. Sometimes in tuning it is advisable to short circuit the con
denser of the wavemeter. A test will readily determine if this is necessary. Be sure in
FIG. 6
Wavemeter constructed of form wound duo-lateral or similar coil and variable condenser. This wavemeter will cover any range by changing the size of the coils. The proper size coil to use is shown in the table given below
WAVELENGTH RANGE OF VARIOUS DUO-LATERAL COILS
No. 2ooA
No. 200 B
No. 2ooC
No. 2ooD
No. 2ooE
3 PLATE
5 PLATE
1 1 PLATE
21 PLATE
43 PLATE
CAPACITY RANGE OF CONDENSER IN
MAX.
49
9'
208
418
877
MICRO MICRO
MIN.
7
8
10
13
21
FARADS
/
COIL NUMBERS
WAVE
WAVE
WAVE
WAVE
WAVE
LENGTHS IN
LENGTHS IN
LENGTH IN
LENGTH IN
LENGTH IN
METERS
METERS
METERS
METERS
METERS
Min.
Max.
Min.
Max.
Min.
Max.
Min.
Max.
Min.
Max.
US or MS 25. .
75
105
75
130
75
1 80
120
245
120
355
US or MS 35. .
105
'45
105
'75
105
245
160
335
160
480
U S or M S 50.
'45
205
'45
250
150
355
220
485
220
690
US or MS 75. .
195
290
200
365
2IO
520
340
7'5
340
1 020
U S or M S i oo .
250
380
255
475
260
675
430
930
430
1330
U S or M S 150.
335
550
340
705
355
1 020
680
1410
680
2060
U S or M S 200.
435
730
445
935
465
'359
900
1880
900
2700
U S or M S 249 .
535
910
560
1 170
575
1700
I IOO
2370
I IOO
3410
U S or M S 300 .
680
I 120
690
1430
720
2140
1400
2870
1400
4120
U S or M S 400.
830
'450
870
1880
890
2750
1800
3830
1800
5500
U S or M S 500.
1050
1840
1080
2390
1 1 20
3430
2300
4870
2300
7000
U S or M S 600.
1270
2200
1300
2840
1360
4130
2800
5700
2800
8200
U S or M S 750.
1600
2760
1680
3570
1710
5100
3500
7200
3500
10400
U S or M S 1000.
2090
3660
2140
4750
2240
6900
4700
9600
4700
13800
U S or M S 1250.
2570
4670
2640
6000
2770
8900
6000
12500
6000
18000
U S or M S 1500.
3320
5800
3400
7500
3570
1 1000
7500
15400
7500
22 IOO
NOTE— In making calculations of the 21 and 43-plate condensers a minimum capacity of 100 micromicro farads has been assumed which includes the capacity of accessories in the circuit