GW Instek GRF-1300A User Manual
Page 101
RF Communication and Signals Experiments
Substituting U
0
1
1
1
2
2
3
3
2
2
2
2
1
1
2
2
3
3
3
3
3
3
1
1
2
2
3
3
3
1
3
2
3
1
2
3
1
2
3
1
2
( cos
cos
cos
)
(
cos 2
cos 2
cos 2 )
(
cos 3
cos 3
cos 3 )
....
cos(
)
cos(
)
cos(
2
)
cos(
2 )
cos(
)
...
P
q
m
n
x
i
A
A u
t u
t u
t
A u
u
u
A u
u
u
A
t A
t
A
t
A
t
A
k
r
s
t
ω
ω
ω
ω
ω
ω
ω
ω
ω ω
ω ω
ω
ω ω
ω ω
ω
ω
ω
ω
=
+
+
+
+
+
+
+
+
+
+ +
± +
+
± ±
+
± +
±
+
± +
±
+
+
+
+
ω
Where, the A0 term is the DC component items, the A1 term is
the fundamental term, while the A2 term and the A3 term are the
2nd and 3rd order harmonics, respectively. Higher harmonic
components have been ignored. These frequency components are
produced after the mixer and are filtered out with a bandpass
filter. They do not affect any subsequence stages. The Ap and Aq
terms are useful IF terms and should be received by the receiver
normally. The Am and An components are the third-order
intermodulation frequency components and they also contribute
to channel interference. It is difficult to use filters to filter out the
third-order intermodulation interference. The most effective
means of reducing third order interference is by designing and
producing a mixing device with good linearity. Integrated mixing
devices usually express the level of third-order intermodulation
interference using the IP3 point (third order intermodulation
intercept point). A large IP3 value indicates a mixer with good
linearity. Circuit design that minimizes the amplitude of the RF
signal input so that the mixer operates more linearly can also
reduce third order intermodulation products.
2. The main parameters of the frequency mixer
The main technical indicators in the frequency mixer include
conversion gain, 1dB compression point, port isolation and so on.
(1) Conversion gain
The ratio of RF input power level to the output signal
power level is called conversion gain, Gc. I.e.,
99