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Toko 8541660
Ludwig Puller, OE1LPW, send me a couple of 1:4 transformers that were designed for pulse processing on computer boards. They are made by TOKO and the type is "8541660". Probably they are not produced anymore but it still is interesting to see what result this kind of transformer gives in the H-Mode mixer circuit. Although a little bit too big, they could be soldered on DIP6 sockets so it was no problem to mount them on an unmodified mixer board. The results are shown in the following table:
| FSA3157 + 8541660 + 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 |
4,84 |
134,0 |
130,5 |
38,8 |
|
|
|
40,9 |
|
|
2,5 |
40,9 |
| 80 |
1,4 |
4,84 |
134,0 |
132,0 |
38,0 |
|
40,2 |
40,2 |
40,2 |
40,2 |
40,2 |
2,5 |
40,2 |
| 40 |
2,3 |
4,96 |
134,0 |
131,0 |
38,8 |
|
|
|
39,2 |
|
|
2,5 |
39,2 |
| 30 |
3,4 |
5,04 |
134,0 |
130,0 |
36,4 |
|
|
|
38,8 |
|
|
2,5 |
38,8 |
| 20 |
3,4 |
5,16 |
133,5 |
130,0 |
38,0 |
|
|
|
37,9 |
|
|
2,5 |
37,9 |
| 17 |
3,0 |
5,16 |
133,5 |
130,0 |
35,2 |
|
|
|
37,3 |
|
|
2,5 |
37,3 |
| 15 |
3,9 |
5,16 |
133,0 |
128,0 |
47,6 |
9,4 |
|
|
36,9 |
|
|
2,5 |
36,9 |
| 12 |
3,7 |
5,32 |
132,5 |
127,5 |
38,8 |
|
|
|
35,3 |
|
|
2,5 |
35,3 |
| 10 |
2,3 |
5,60 |
132,5 |
129,0 |
39,6 |
|
|
|
35,0 |
|
|
2,5 |
35,0 |
| 6 |
|
7,08 |
128,5 |
|
30,8 |
|
|
|
37,0 |
|
|
2,5 |
37,0 |
| 4 |
|
8,12 |
121,0 |
|
38,0 |
|
|
|
29,6 |
|
|
2,5 |
29,6 |
Conversion loss is excellent on the HF bands! But on 6M and 4M the IL is rapidly rising making the Toko transformers less useable at those frequencies.
The mixers intercept point is at its best on 160M at +40.9dBm and slowly but steadily drops off to around +35dBm on 10M. It follows 3rd order law perfectly as can be seen from the 80M results. Interesting too is that these transformers have no noticeable sensitivity to the mixers bias point at all. So far all other 1:4 transformers tested were very sensitive to the bias point and usually peeked in IP3 around 40M or 80M. This effect is totally absent with the Toko transformers.
RF-IF isolation is rather poor, just below -40dB, even if band specific adjustments are made. The levels in the table are for the best isolation on each band.
Average spur level on 15M is poor at +9,4dB. Note that this applies to a mixer adjusted for best RF-IF isolation, so nothing special was done to minimize the spur level. The symmetry of the mixer is not very good, probably caused by small differences between the 3 transformers. Given the RF-IF isolation result, a low spur level was not expected.
All together the TOKO pulse-formers did reasonably well given the fact that they were not designed for this purpose. It shows that a wide range of transformers can be used with quite good results in the H-Mode mixer circuit!
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