Download Assembly Procedure SMD Attenuators

PI& T Attenuators
Version
This document is for printed circuit board version 0.0a for both the PI and T attenuators.
Overview & Features:
The PI and T attenuators use 0805 resistors and for most values of attenuation will be
accurate to within 0.25dB from DC to 3GHz.Note that resistor values above about 100
ohms will adversely impact high frequency response. For more detail see the attenuation
graphs in the performance section.
The resistor table below provides the resistor values, actual attenuation and expected
return loss. In general the T attenuator configuration will provide better frequency
response for high attenuator values because of the lower resistor values used.
 Attenuators are symmetrical the input and output impedance is 50 ohms
 1% resistor values are used and result in ideal accuracy typically better than 0.1dB
 Maximum input power is +23dBm
Circuit Description
0805 size surface mount resistors R1 to R3 form the attenuator. The attenuation table
below gives resistor values for different values of attenuation. J1 is a male SMA edge
mount connector and J2 a female edge mount connector. The PCB is 20 x 10mm.
Schematics& PCB PI Attenuator
Schematics & PCB T Attenuator
VE3CZ0
PI & T Attenuators
1/5
Resistor Table
The following table shows the 1% resistor values used for various PI and T attenuators
along with their ideal attenuation and return loss.
Attenuator Resistor Values
Atten
dB
1
2
3
4
5
6
7
8
9
10
12
13
15
16
18
20
25
30
35
40
R1
Ohms
5.76
11.5
17.4
23.7
30.1
37.4
45.3
52.3
61.9
71.5
93.1
107
137
154
196
249
442
787
1400
2490
PI Attenuator
R2 & R3 Atten
Ohms
dB
866
1.00
432
2.00
294
2.97
221
3.99
178
4.98
150
6.01
130
7.06
115
8.00
105
9.02
95.3 10.07
84.5 11.93
78.7 13.06
71.5 15.05
68.1 16.08
64.9 17.97
61.9 19.95
56.2 24.95
53.6 29.92
51.1 35.08
51.0 39.97
RL
dB
70.6
54.8
63.1
61.2
53.7
67
64.3
47.4
61.2
53.8
49.4
64.1
77.7
48.3
49.6
44.7
54.9
50.9
43.5
77.4
R1 & R3
Ohms
2.87
5.76
8.45
11.3
14.0
16.5
19.1
21.5
23.7
26.1
30.1
31.6
34.8
36.5
38.3
41.2
44.2
46.4
48.7
48.7
T Attenuator
R2 Atten
Ohms
dB
432
1.00
215
2.01
143
2.97
105
3.99
82.5
4.99
66.5
6.00
56.2
6.97
47.5
7.98
40.2
9.02
34.8 10.07
26.7 12.05
23.7 12.95
18.2 15.04
16.2 16.05
12.7 17.96
10.2 20.00
5.62 24.95
3.16 29.92
1.78 35.07
1.00 39.95
RL
dB
72.6
68.7
64.5
87.6
67.7
52.0
60.6
68.0
50.8
73.9
58.1
69.3
53.3
56.8
44.4
44.9
46.0
45.3
47.0
50.1
Assembly Equipment you’ll need





Surface Mount Device (SMD) soldering kit
o Temperature controlled soldering iron with fine tip. Insure the tip is grounded!
o Small vise to hold the PCB
o Liquid no clean solder flux
o Two pair of SMD Tweezers
o Isopropanol 99%
o Cotton swabs
Electrostatic Discharge (ESD) protection - mat - wrist strap
Needle nose pliers
Heat gun for heatshrink
Scissors
Before You Begin
VE3CZ0
PI & T Attenuators
2/5


Check the contents of the kit to make sure that none of the parts are missing.
Print out this document to help locate components on the printed circuit board.
Assembly Tips
1. Use two pair of tweezers, one for pulling up the hold down tape on the parts sheet and
opening the SMD part carrier, and the other for mounting components on the PCB. This
prevents the tape glue residue from getting on the tweezers used for SMD mounting
work.
2. If adhesive does get onto the tweezers’ tips, parts will stick to them. If this happens wet a
cotton swab with isopropyl alcohol. Spread the tweezers tips to clamp around the swab
and draw them across the swab to clean the tips.
3. Orient all resistors that have values marked on them in the same direction so that they
can more easily be read and identified after installation. Use the same orientation as is
used on the PCB silk screen.
4. As you go through each assembly section check off components in the square box
beside the component identifier as you install devices.
Assembly
1. Install all top side PCB components
 R1 Per table of Attenuator Resistor Values
 R2 Per table of Attenuator Resistor Values
 R3 Per table of Attenuator Resistor Values
In the next step SMA PCB edge mount connectors are installed. Fit each connector into
the PCB and align it so that the center pin is in the middle of the PCB’s coplanar
waveguide track. Also make sure the SMA connector is square to the end of the PCB.
Solder the center conductor first then the two top ground plane connectors. Then turn
the PCB over and solder the bottom side ground plane leads.
 J1
SMA edge mount male
 J2
SMA edge mount female
Physical Assembly
Use the scissors to cut the attenuation value out of the label that held the SMA parts. Cut
along the cell guidelines and place the attenuation value on the PCB top side nesting it
between the SMA connectors. Place the heat shrink over the assembly then apply heat to
the heat shrink. Carefully manage the position of the heatshrink as the heat gun may blow
it about. You may want to hold the heat shrink in place by using tweezers to hold it against
the PCB. It should be positioned so that it willnot interfere with the male SMA nut, and
stretches out over the female connector covering a portion of the threads.
Electrical Performance
The following graphs show typical attenuation versus frequency performance for the 3 and
10 dB PI and T attenuators. Note that the vertical scale is 0.2dB for the 3db attenuators
and 2dB for the 10dB attenuators.
VE3CZ0
PI & T Attenuators
3/5
VE3CZ0
PI & T Attenuators
4/5
VE3CZ0
PI & T Attenuators
5/5