Where the
Competitive
Receiver Starts
-The First Mixer
Bob DePierre
August, 2009
Out-of-Passband Signals Cause
In-Passband Interference
-Once it gets through the mixer, no filter can get rid of it.
-Third-order distortion usually dominates.
-Some mixers handle overload better than others.
f1
f2
2*f1-f2
2*f2-f1
Mixer = Distortion Device
• 1960’s breakthrough was
the balanced mixer.
• SBM => RF balanced out.
• DBM => LO also balanced
out.
• Exponential behavior
really bad for giant signals.
i = I S (e
v
VT
− 1)
2
3
x
x
e = 1 + x + + + ...
2! 3!
x
1 id
16.0m
1
Plot1
id in amperes
12.0m
8.00m
4.00m
0
160m
200m
240m
vd in volts
280m
320m
Why the FET Mixer?
Diode Ring DBM - Exponential
2 mag(fft(temp))
RF
6
5
R4
.001
4
L2
1u
L4
L6
8
X4
BAT720
L1
1u
V1
L4
L5
X1
BAT720
IF
3
L1
L3
10
L5
1u
RIF
50
RLO
50
L4
1u
7
V9
9
L6
1u
2
L1
L2
LO
1
X2
BAT720
X3
BAT720
L3
1u
L5
L6
VLO
L2
L3
Plot1_f
mag(fft(temp)) in volts
100u
RRF
50
10u
1u
100n
10n
1n
2
3.00Meg
9.00Meg
15.0Meg
frequency in hertz
21.0Meg
27.0Meg
Orion 4 JFET DBM – Square Law
18
RF
V1
11
L2
1u
L1
1u
14
C3
72p
J4
J310
R8
680
R9
5k
L3
1u
L1
L3
C6
330p
R11
5k
RIF
200
R12
5k
J2
J310
R3
47
C4
0.001u
C7
0.1u
6
10
R6
680
L11
1u
J1
J310
C5
0.001u
13
L2
L3
IF
L10
1u
7
R10
5k
15
L1
L2
1m
L10
L11
16
2
IR13
12
C2
0.001u
RRF
50
1
2 mag(fft(temp))
R13
.01
J3
J310
R5
680
R7
680
17
L7
1u
R4
50
LO
L9
1u
10u
2
1u
LO
L9
L7
9
100n
8
L7
L8
100u
L8
1u
3
4
V2
13
5
Plot1_f
mag(fft(temp)) in volts
C1
0.001u
L9
L8
2.00Meg
6.00Meg
10.0Meg
frequency in hertz
14.0Meg
18.0Meg
Receiver Architectures
• Superheterodyne
Bandpass
Filters
First
Mixer
Narrow
Filters
Gain
Detector
Local
Oscilllator
• Direct Conversion
Bandpass
Filters
First
Mixer
Lowpass
Filter
Audio
Gain
Output
Device
Audio
Gain
Output
Device
Mixer Test Procedures
•
•
Input Signals = -25dBm, Spacing 20 kHz, 2 kHz
“Invasive” Measurement at Output Port of First Mixer
Receiver
Under
Test
Marconi
2018A
SignalGenerators
Hybrid
Combiner
Hi-Z
FETProbe
HP
8657A
Agilent
8595E
SpectrumAnalyzer
GPIB to PC
Intercept Graph
Used to Calculate the IP
E
Power Out(dBm)
C
D
B
A
Power In(dBm)
F
Mixer Structures
• BJT Gilbert Cell
• Diode DBM
• 2 JFET SBM
• 4 JFET DBM
• Fast Switching Multiplexer
BJT Gilbert Cell
•
•
•
•
SA612 chip in wide use
Double Balanced, but with no transformers
Elecraft KX-1
Q-Track receivers
BJT Gilbert Cell in KX-1
Wide Spacing
• Gain= +18.7 dB
• Distortion= 46.1dB
down
• IP= -1.9 dBm
Diode DBM Mixer
• MiniCircuits TUF-1 in
Elecraft K2
• Workhorse high
performance mixer of
the 80’s—90’s
• Transformers balance
the RF and LO signals
out of the IF port
Diode DBM Mixer in K2
ATTN off; 3 kHz Spacing
• 14dB Preamp On
• Gain= +11.2dB
• Distortion 46dB
down
• IP= +4.85dBm
• Phase noise very
close in only
2 JFET SBM in Pegasus
• Balanced only at
RF port
• Standard J310
FETs
2 JFET SBM in Pegasus
ATTN off, 20 kHz Spacing
• Gain= -9.5dB
• Distortion 56.2dB
down
• IP= +3.3dBm
• Noise at graph edge
–100dBm
2 JFET SBM in Pegasus
ATTN on, 20 kHz Spacing
•
•
•
•
Gain= -17.6dB
Distortion 62dB down
IP= +6dBm
Noise at graph edge
–95dBm
2 JFET SBM in Pegasus
ATTN off, 2 kHz Spacing
• Gain= -11.7dB
• Distortion 47dB
down
• IP= -1.5dBm
• Noise at graph edge
–98dBm
2 JFET SBM in Pegasus
ATTN Switched, 2 kHz Spacing
• ATTN on/off
4 JFET DBM in TS850
• Discrete components
• All 3 ports have
balancing
transformers
4JFET DBM in TS850
Preamp On, 20 kHz Spacing
• Gain= +1.4dB
• Distortion 47dB
down
• IP= -1.5dBm
• Noise at graph edge
–110dBm
4 JFET DBM in TS850
Preamp Off, 20 kHz Spacing
• Gain= -6.6dB
• Distortion >71.8dB
down
• IP= +13.55dBm
• Noise at graph edge
–105dBm
4 JFET DBM in TS850
Preamp On, 2 kHz Spacing
• Gain= +4.7dB
• Distortion 34dB
down
• IP= -8.0dBm
• Noise at graph edge
–85dBm
4 JFET DBM in TS850
Preamp Off, 2 kHz Spacing
• Gain= -10.5dB
• Distortion 61.4dB
down
• IP= +5.7dBm
• Noise at graph edge
–95dBm
4 JFET DBM in TS850
Preamp Off, 2 kHz Spacing
• Gain= -7.9dB
• Distortion 60.3dB
down
• IP=+5.1dBm
• Noise at graph edge
–100dBm
4 JFET DBM in FT950
• JFETs and
transformers in
modules
• All 3 ports have
balancing
transformers
4 JFET DBM in FT950
Preamps Off, 20 kHz Spacing
• Gain=-3.3dB
• Distortion >80dB
down
• IP>+14.8dBm
• Noise at graph edge
–110dBm
4 JFET DBM in FT950
Preamps On, 20 kHz Spacing
• Gain= +16.3dB
• Distortion 46.7dB
down
• IP= -1.7dBm
4 JFET DBM in FT950
Preamp #1 On, 20 kHz Spacing
• Gain= +8.1dB
• Distortion 64.9dB
down
• IP= +7.4dBm
• Noise at graph edge
–100dBm
4 JFET DBM in FT950
Preamps Off, 2 kHz Spacing
• Gain= -2 dB
• Distortion >60.8dB
down
• Noise at graph edge
–92dBm
4 JFET DBM in IC756Pro
• Components
inside well
shielded
enclosures
• Measured outside
enclosure at Q501
4 JFET DBM in IC756Pro
Preamp #2 On, 20 kHz Spacing
•
•
•
•
•
Input= -25dBm
Gain= -23.4dB
Dist 46.3dB down
IP= -1.85dBm
Noise at graph edge
–113dBm
4 JFET DBM in IC756Pro
Preamp #1 On, 20 kHz Spacing
•
•
•
•
•
Input= -20dBm
Gain= -31.3dB
Dist 55.2dB down
IP= +6.3dBm
Noise at graph edge
–115dBm
4 JFET DBM in IC756Pro
Preamps Off, 20 kHz Spacing
•
•
•
•
•
Input= -10dBm
Gain= -42.5dB
Dist 48dB down
IP= +14.0dBm
Noise at graph edge
–115dBm
4 JFET DBM in IC756Pro
Preamps Off, 2 kHz Spacing
• Input= -15dBm
• Gain= -40dB
• Phase Noise Covers
the Distortion
• IP= +13.7dBm
• Noise at graph edge
–115dBm
4 JFET DBM in IC756
Preamp #1 On, 2 kHz Spacing
•
•
•
•
•
Input= -15dBm
Gain= -30dB
Dist 42 dB down
IP= +6.0dBm
Noise at graph edge
–108dBm
4JFET DBM in Orion
• Discrete
components
• Balancing
transformers at 2
ports
4 JFET DBM in Orion
Preamp Off, 20 kHz Spacing
•
•
•
•
•
Input= -15dBm
Gain= +11.2dB
Dist 55dB down
IP= +12.6dBm
Noise at graph edge
–120dBm
4 JFET DBM in Orion
Preamp On, 20 kHz Spacing
•
•
•
•
•
Input= -25dBm
Gain= +22.7dB
Dist 47.2dB down
IP= -1.38dBm
Noise at graph edge
–115dBm
4 JFET DBM in Orion
Preamp Off, 20 kHz Spacing
•
•
•
•
•
•
ATTN= 6dB
Input= -15dBm
Gain= +5.6dB
Dist 67.3dB down
IP= +18.7dBm
Noise at graph edge
–95dBm
4 JFET DBM in Orion
Preamp Off, 2 kHz Spacing
•
•
•
•
•
•
ATTN= 6dB
Input= -10dBm
Gain= +4.8dB
Dist 55dB down
IP= +17.6dBm
Noise at graph edge
–73dBm
4 JFET DBM in Orion
Preamp On, 2 kHz Spacing
• Input= -35dBm
• Gain= +24.1dB
• Phase Noise covers
the Distortion
• IP= -1.2dBm
• Noise at graph edge
–79dBm
2 JFET SBM in Orion Sub
20 kHz Spacing
•
•
•
•
Input = -25dBm
Gain= 2.2dB
Dist= 66.2dB down
IP= +8.1dBm
2 JFET SBM in Orion Sub
2 kHz Spacing
• Input= -25 dBm
• Gain= +6.4dB
• Phase Noise covers
the Distortion
• IP= +4.4dBm
• Noise at graph edge
–83dBm
Mux Mixers – K3
• Double Balanced With
transformers at 2 ports
• CBT3257 chip, 21¢
Mux Mixers – Softrock & Flex
• Tayloe Mixer
– Sampling Integrator
– Direct Conversion
Receiver Only
• FST3253 chip, 17¢
• Requires I/Q Inputs
1 i
2 q
Plot1
i in volts
4.50
3.50
1
2.50
1.50
500m
Plot2
q in volts
4.50
3.50
2
2.50
1.50
500m
1.00u
3.00u
5.00u
time in seconds
7.00u
9.00u
Mixer vs Rig Rundown
Mixer Type
Rig
IP Range
BJT Gilbert Cell
Elecraft KX-1
< 0 dBm
Diode Double Balanced Elecraft K-2
0 to +5dBm
2 JFET Single Balanced TenTec Pegasus, Jupiter,
Orion Sub, IC-746
0 to +5 dBm
4 JFET Double
Balanced
FT950, TS850, IC756,
Orion Main
+10 to +15
dBm
Fast Switching
Multiplexer
K-3, Flex, Softrock
The “Ultra” Rigs
20 kHz Spacing
Orion
+12.0 dBm (+18.6 dBm with 6dB ATTN)
TS850
+13.55 dBm
IC756 Pro
+14.0 dBm
FT950
+14.8 dBm
2 kHz Spacing
IC756 Pro
+13.7 dBm
Orion
+17.6 dBm (with 6dB ATTN)
And the Conclusion is:
The 4 JFET DBM has become
so good that it doesn’t pay to
improve it until we improve
phase noise at its output!