|
Fairchild FSA3157
The FSA3157 (SC70-6 package) contains only a single SPDT switch. Therefore 2 units are needed to implement the H-Mode mixer. The PCB layout of the 2xFSA3157 with the 3 TT4-1A transformers is ultra compact because the 2 switches can be placed very close to the corresponding transformers without compromising the distance between the outer transformers. The FSA3157 does not require an 74AC74 divide by two squarer as it does not need both Q and !Q.
The following table lists the results with the FSA3157 and the 74AC74 div2 squarer:
| FSA3157 + TT4-1A + 74AC74 |
Vdd = 7.0V, Vbias = 2.5V |
Best bias |
| Band |
BPF |
mixer |
MDS -dBm |
IF rej |
spur |
mixer IIP3 (dBm) @ 20KHz spacing |
Bias |
IIP3 |
| IL |
CL |
- |
+ |
|
avg |
-6 |
-3 |
0 |
+3 |
+5 |
|
0 |
| -dB |
-dB |
BPF |
BPF |
-dB |
dB |
dBm |
dBm |
dBm |
dBm |
dBm |
V |
dBm |
| 160 |
3,3 |
5,08 |
132 |
129 |
45,6 |
|
|
|
41,4 |
|
|
3,0 |
41,4 |
| 80 |
1,4 |
5,00 |
133 |
131 |
47,2 |
|
45,2 |
46,7 |
47,7 |
51,5 |
50,0 |
2,1 |
49,5 |
| 40 |
2,3 |
5,00 |
133 |
130 |
49,6 |
|
|
|
44,9 |
|
|
2,4 |
44,9 |
| 30 |
3,4 |
4,96 |
133 |
129 |
44,8 |
|
|
|
43,5 |
|
|
2,5 |
43,5 |
| 20 |
3,4 |
4,96 |
133 |
129 |
40,8 |
|
|
|
41,9 |
|
|
3,0 |
41,9 |
| 17 |
3,0 |
4,96 |
133 |
129 |
41,2 |
|
|
|
40,3 |
|
|
2,5 |
40,3 |
| 15 |
3,9 |
4,96 |
133 |
129 |
41,6 |
-2,9 |
|
|
39,6 |
|
|
2,6 |
39,6 |
| 12 |
3,7 |
4,92 |
133 |
129 |
36,8 |
|
|
|
38,6 |
|
|
2,8 |
38,6 |
| 10 |
2,3 |
4,96 |
133 |
130 |
33,2 |
|
|
|
37,0 |
|
|
2,8 |
37,0 |
| 6 |
|
5,48 |
131 |
|
41,2 |
|
|
|
35,2 |
|
|
3,0 |
35,2 |
The FSA3157 is tested at 7V Vdd with bias at 2,5V. 2.5V seems to be a good compromise for all bands. The best bias point per band followed a pattern similar to the bias point pattern of the NC7SZ384. The IMD dip is most profound on 80M where IMD could be almost nulled-out. From 20M and higher there is not much of a dip left and the bias point goes up.
I am not able to measure at -6dBm reliably as the 3rd IMD products are too close to the noise floor.
Very high IIP3, however again degrading with frequency and peaking on 80M and 40M.
160M performance seems to suffer from the transformers limitations.
The spur reduction on 15M is surprisingly good indeed with -2,9dB!
Unlike the other mixers with the SPDT type switches, the 9MHz IF rejection is rather good at below -40dB fairly constant on most bands!
MDS level on 6M and RF-IF isolation are rather good too!
Back to Switches
Back to the TOC
|
