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Homemade FT37-43
To test the performance of the homemade FT37-43 transformers mentioned earlier the FSA3157 with 74AC04 squarer is used at the usual voltages. The transformers are made up with 11 trifilar windings of 0.3 enameled wire on FT37-43 ferrite toroids. The 3 transformers are made as identical and symmetrical as possible.
| FSA3157 + FT37-43 + 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 |
4,60 |
133,5 |
130,0 |
28,8 |
|
|
|
42,9 |
|
|
3,0 |
42,9 |
| 80 |
1,4 |
4,52 |
133,5 |
131,5 |
28,8 |
|
46,7 |
47,7 |
47,7 |
45,7 |
39,2 |
2,5 |
47,7 |
| 40 |
2,3 |
4,56 |
133,5 |
130,5 |
28,8 |
|
|
|
41,4 |
|
|
2,5 |
41,4 |
| 30 |
3,4 |
4,60 |
133,5 |
129,5 |
28,4 |
|
|
|
44,0 |
|
|
2,4 |
44,0 |
| 20 |
3,4 |
4,68 |
133,5 |
129,0 |
30,4 |
|
|
|
40,9 |
|
|
2,3 |
40,9 |
| 17 |
3,0 |
4,80 |
133,5 |
130,0 |
28,4 |
|
|
|
39,8 |
|
|
2,5 |
39,8 |
| 15 |
3,9 |
4,68 |
133,5 |
129,0 |
26,8 |
8,7 |
|
|
39,1 |
|
|
2,7 |
39,1 |
| 12 |
3,7 |
4,96 |
133,0 |
129,0 |
30,4 |
|
|
|
37,8 |
|
|
2,7 |
37,8 |
| 10 |
2,3 |
4,92 |
133,0 |
130,0 |
27,2 |
|
|
|
35,5 |
|
|
3,0 |
35,5 |
| 6 |
|
6,68 |
129,0 |
|
28,0 |
|
|
|
36,5 |
|
|
3,0 |
36,5 |
| 4 |
|
|
|
|
|
|
|
|
33,9 |
|
|
2,7 |
33,9 |
The slightly lower conversion loss is clearly showing in the MDS levels.
IP3 is not substantially better than with TT4-1A's as one would expect from the measurement of the transformers alone. Remarkable is the lower performance on 40M and the reduced IP3 at higher input levels on 80M with these transformers.
It is also interesting to see that the same mixer switches with different transformers give sometimes significant changes in the optimum bias point. This is probably the same effect as noted on the input termination.
VHF performance is degrading rapidly with these transformers.
Adjustment for minimal spur level was also possible with this arrangement, but no effort has been spent to see if it worked equally well as with the TT4-1A's. Average spur levels on 15M are rather loud with 8.7dB. Obtaining good VHF symmetry with FT37-43 toriod transformers is not easy.
Altogether this table shows that the rather expensive TT4-1A's are not the only way to build the H-Mode mixer with good results for the HF bands.
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