NOTE
Electromagnetic waves (carrier and both side bands) are transmitted as
single group in AM form.
Side bands are USB, higher than carrier
frequency.
LBS is lower than carrier frequency. Either USB signal
or LSB signal is transmitted, and it depends upon individual circumstances.
Usually for amateur communication, LSB is used under 10 MHz and USB over
10 MHz.
SSB waves are generated by passing AM wave through band pass
filter, then selecting either USB or LSB and sending signal through
t r a n s m i t t i n g a n t e n n a .
In receiving SSB (USB or LSB) waves on ordinary
AM receiver, it is not possible to hear transmitted voice unless special
alteration is made at detection stage.
I t i s p o s s i b l e e i t h e r t o c o n s t r u c t
carrier and detect AM after adding SSB or to use switching method
(product detection) on frequency of carrier for SSB. Latter method ha s
l e s s d i s t o r t i o n a n d i s u s e d i n t h i s u n i t .
Continuous Waves (CW).
In practice, these waves are used to transmi t
M o r s e c o d e s i g n a l s b y i n t e r m i t t e n t c a r r i e r , b u t i t i s d i f f i c u l t t o h e ar
sound even after AM detection.
U s i n g d e t e c t i o n c i r c u i t o f S S B , i n t e r-
mittent sound can be heard by product-detecting carrier and by varying
f r e q u e n c y a l i t t l e.
Set up radio receiver same as for SW reception.
(a) Before tuning in desired signal, turn BFO switch on.
( b ) T u n e i n d e s i r e d s i g n a l .
( c ) C a r e f u l l y m o v e B F O p i t c h c o n t r o l u n t i l s i g n a l i s c l e a r e s t.
NOTE
In receiving two-way communication signals, possible difference between
two frequencies may require another BFO pitch control adjustment.
Table 9-2. METER AND AMATEUR RF BANDS
BANDWIDTH
DESCRIPTION
120 m (2.3-2.495 MHz) and 90 m (3.2-3.4 MHz)
These two bands are used solely in tropical regions where unusual electri-
cal activity and other types of noise make MW (AM) reception impractical
They are used mainly for local broadcasting.
In comparison with MW, they are
d i f f i c u l t t o r e c e i v e b e c a u s e o f n o i s e o r i n t e r m i t t e n t s i g n a l s.
75 m Band (3.9-4.0 MHZ)
Used for short-distance broadcasting in tropical regions.
TM 5-6675-318-14
9 - 44
