Discrete transformerless DBM question
时间：04-04
整理：3721RD
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Hi,
In figure 5 of this page http://www.intio.or.jp/jf10zl/gil.htm a discrete transformerless DBM is shown.
Google translate says (his english translation is not too good):
" I actually tried the circuit of Figure 5 and tried it. As for the result, I got a one pass and DBM with good characteristics like the photo was made. Adjusting the modulation wave with the carrier wave constant at 70 mV gave a gain of about 17 dB. It is about the same as the product of the manufacturer. I checked the maximum output amplitude up to 270 mVc - p, but with my own Vienna bridge oscillator I could not see any more waves, so I could not confirm any more. Well enough. However, carrier suppression alone did not match the manufacturer's products. By adjusting the semi-fixed resistance of 5 k ohm for balancing adjustment written as "BALANCEADJUST" in the figure, it was possible to observe that the point where the carrier can be adjusted to the minimum and the point where the passing through of the modulation signal can be adjusted to the minimum is different . This is a lot of fun. If 5 k ohm semi-fixed resistor for equilibrium adjustment is not installed, carrier suppression will deteriorate by about 10 dB further. It is not something I could call DBM any longer. In manufacturer's IC, this is not adjusted, so it is expected that the IC's internal transistors are homogeneous as expected. By the way, in this case, all the transistors are randomly chosen from the items packed in 200 bags in the same bag of Y in 2 SC 1815."
This translation is not good either, but what I understand is that by adjusting the balance potentiometer, he cannot achieve minimum RF carrier and minimum AF output simultaneously. That is, the RF is suppressed at an optimum balance setting, but the input signal has not maximum suppression at the output.
1. Is my understanding right?
2. I intend to use this DBM for audio frequencies (for audio spectrum inversion), so both input signals will be close in audio frequencies.
Do you think that I could achieve optimum suppression for both output signals, since the input signals are both AF?
3. Finally, he has not matched the transistors. Is that ok to use a cheap multimeter with embedded matching to match them for beta gain? I do not seek extreme performance, of course, but I guess ot could be better to match them, even for beta.
In figure 5 of this page http://www.intio.or.jp/jf10zl/gil.htm a discrete transformerless DBM is shown.
Google translate says (his english translation is not too good):
" I actually tried the circuit of Figure 5 and tried it. As for the result, I got a one pass and DBM with good characteristics like the photo was made. Adjusting the modulation wave with the carrier wave constant at 70 mV gave a gain of about 17 dB. It is about the same as the product of the manufacturer. I checked the maximum output amplitude up to 270 mVc - p, but with my own Vienna bridge oscillator I could not see any more waves, so I could not confirm any more. Well enough. However, carrier suppression alone did not match the manufacturer's products. By adjusting the semi-fixed resistance of 5 k ohm for balancing adjustment written as "BALANCEADJUST" in the figure, it was possible to observe that the point where the carrier can be adjusted to the minimum and the point where the passing through of the modulation signal can be adjusted to the minimum is different . This is a lot of fun. If 5 k ohm semi-fixed resistor for equilibrium adjustment is not installed, carrier suppression will deteriorate by about 10 dB further. It is not something I could call DBM any longer. In manufacturer's IC, this is not adjusted, so it is expected that the IC's internal transistors are homogeneous as expected. By the way, in this case, all the transistors are randomly chosen from the items packed in 200 bags in the same bag of Y in 2 SC 1815."
This translation is not good either, but what I understand is that by adjusting the balance potentiometer, he cannot achieve minimum RF carrier and minimum AF output simultaneously. That is, the RF is suppressed at an optimum balance setting, but the input signal has not maximum suppression at the output.
1. Is my understanding right?
2. I intend to use this DBM for audio frequencies (for audio spectrum inversion), so both input signals will be close in audio frequencies.
Do you think that I could achieve optimum suppression for both output signals, since the input signals are both AF?
3. Finally, he has not matched the transistors. Is that ok to use a cheap multimeter with embedded matching to match them for beta gain? I do not seek extreme performance, of course, but I guess ot could be better to match them, even for beta.