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Mini-Circuits T4-1
No H-Mode mixer comparison would be complete without an assessment of the T4-1 transformer as it is known for its very good IP3 behavior be it with slightly higher conversion losses. The following table lists the results with the T4-1:
| FSA3157 + T4-1 + 74AC04 |
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 |
5,60 |
133 |
129 |
46,8 |
|
|
|
41,4 |
|
|
2,5 |
41,4 |
| 80 |
1,4 |
5,56 |
133 |
131 |
47,2 |
|
43,2 |
44,7 |
45,7 |
47,2 |
48,5 |
2,2 |
45,7 |
| 40 |
2,3 |
5,60 |
133 |
130 |
48,4 |
|
|
|
48,9 |
|
|
1,2 |
50,7 |
| 30 |
3,4 |
5,60 |
133 |
129 |
48,8 |
|
|
|
48,3 |
|
|
1,2 |
49,3 |
| 20 |
3,4 |
5,60 |
133 |
129 |
53,6 |
|
|
|
46,7 |
|
|
1,7 |
49,4 |
| 17 |
3,0 |
5,64 |
133 |
129 |
51,6 |
|
|
|
45,3 |
|
|
2,5 |
45,3 |
| 15 |
3,9 |
5,64 |
133 |
128 |
52,8 |
-3,3 |
|
|
44,9 |
|
|
2,6 |
44,9 |
| 12 |
3,7 |
5,68 |
133 |
127 |
45,6 |
|
|
|
43,6 |
|
|
2,6 |
43,6 |
| 10 |
2,3 |
5,72 |
133 |
129 |
40,0 |
|
|
|
44,0 |
|
|
2,7 |
44,0 |
| 6 |
|
5,88 |
130 |
|
55,6 |
|
|
|
39,7 |
|
|
2,7 |
39,7 |
| 4 |
|
6,16 |
127 |
|
26,8 |
|
|
|
38,1 |
|
|
2,7 |
38,1 |
Conversion loss is 0,6dB worse than with other 4:1 transformers.
Average spur level with the T4-1 is excellent at -3.3dB. Note that this applies to a mixer adjusted for best RF-IF isolation, so nothing special was done to minimize the spur level. RF-IF isolation is good at around -50dB on all bands, if band specific adjustments are made. The levels in the table are for the best isolation on 15M.
The T4-1 combination was ultra sensitive to the bias point. The best bias point was even considerable different between the upper and the lower IMD product on the same band! On 40M to 10M the difference in bias points between the 2 IMD products was even around 1V! Therefore I would characterize this combination as very nervous.. The IP3 values listed in the table are the average of the upper and the lower IP3 values. It would have been possible to find a bias point per band that would have yielded identical upper and lower IMD levels, but I suspect that even adjustments within each band are necessary to maintain the optimum. This does not look realistic.
The T4-1 is the first 4:1 transformer that although being "nervous" actually does greater than +40dBm from 160M-10M combined with excellent spur reduction and good RF-IF isolation.
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