10-12-2020, 10:25 AM
3K3 collector loads may be the best value for maximum output swing but it's not a good way to make a modulator. The output impedance will approximate to 3K3 which isn't ideal.
Looking back at my own 1496 based designs. The 1st snippet is from a burst demodulator so it has a low frequency output. Hence a CT transformer isn't useful. I've already put my Band I modulator in a previous post. The 2nd snippet is from a PAL coder I designed many years ago. I re-used the basic design many times in later designs. I'm not sure why I bothered with decoupling on the CT, possibly to ensure that any unbalanced HF current was kept out of the main supply rail.
Looking back at my own 1496 based designs. The 1st snippet is from a burst demodulator so it has a low frequency output. Hence a CT transformer isn't useful. I've already put my Band I modulator in a previous post. The 2nd snippet is from a PAL coder I designed many years ago. I re-used the basic design many times in later designs. I'm not sure why I bothered with decoupling on the CT, possibly to ensure that any unbalanced HF current was kept out of the main supply rail.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
