Help me with the TX/RX offset in simple transceiver
时间：04-04
整理：3721RD
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Hello, this simple all HF bands transceiver I have designed, has no TX/RX offset, so I need to add one.
A tested way (worked ok, with offset variations depended on frequency), is to add a small value capacitor (~4.7pF) in series with the top end of SW1a, or in series with it's bottom end, depending on which direction the offset needs to be. This can be even variable, for adjusting it.
However, when adding this small capacitor at the top end, this couples much less RF input signal to the transceiver during receive and it becomes insensitive.
And when I add this small capacitor to the bottom end, this couples much less RF to the BJT during TX, so the output power to the antenna is tiny.
What other things I can do to correct the problem? Any ideas to try would be helpful.
An idea I had was to use a small 4.7pf in series with the primary of a step up transformer, at the lower end of SW1a? Then the secondary would be connected to the BJT base. I thought it as a way to step up voltage somehow and at the same time not increasing the capacitance to the ground for the oscillator. I have tried 7T:28T on a small 43 material core and it did not have any power advantage.
Any ideas?
A tested way (worked ok, with offset variations depended on frequency), is to add a small value capacitor (~4.7pF) in series with the top end of SW1a, or in series with it's bottom end, depending on which direction the offset needs to be. This can be even variable, for adjusting it.
However, when adding this small capacitor at the top end, this couples much less RF input signal to the transceiver during receive and it becomes insensitive.
And when I add this small capacitor to the bottom end, this couples much less RF to the BJT during TX, so the output power to the antenna is tiny.
What other things I can do to correct the problem? Any ideas to try would be helpful.
An idea I had was to use a small 4.7pf in series with the primary of a step up transformer, at the lower end of SW1a? Then the secondary would be connected to the BJT base. I thought it as a way to step up voltage somehow and at the same time not increasing the capacitance to the ground for the oscillator. I have tried 7T:28T on a small 43 material core and it did not have any power advantage.
Any ideas?
As far as concern the transformer, I am talking about this technique https://www.edaboard.com/showthread.php?t=368517