Video looking at the microphone amplifier. Aim was for about 20bB gain, with a flat response from 300Hz to 3kHz. The schematic is on the blog at: zl2ctm.blogspo...
Great videos! I use them as guides for how to teach these electronics concepts, your conceptual descriptions are very helpful! If this is helpful, another way to think about how to choose those input and bypass capacitors is to think of them working with the resistors as high pass filters. Then it's simply just an RC filter. The input RC high pass filter is that input capacitor with the parallel combination of the two bias resistors. The bypass capacitor forms another high pass filter with the emitter resistor. Looking at those simple RC fingers will get you your Bode plots right away in an intuitive way.
It is nice to see that you are back on homebrewing radios! If you ever want to try screen-capture, I have a recommendation for you. To capture the screen I have been using OBS (Open Broadcaster Software) its free and quite straightforward to setup. You seem to record your videos in one go, and it is possible to switch between camera and screen-capture while recording with OBS. Regardless of our decision on screen-capture, I will be looking forward for your next video.
if you want to capture the screen output have yo looked at OBS which is free and does a great job, so you can have it on lots pf PC's or just the main one.
Hi Frédéric. If you look at the 2N3904 datasheet you'll see the hFE gain is maximum at 10mA (min 100, max 300). This is a base rig so I can afford to have a higher quiescent Ic in order to maximize the gain.
Is there any high frequency cut off on the amp, i'd put a RF bypass to ground to stop RF trying to get through. Also i'd try and out a low pass filter in there to start to kill the gain after 3KHz. edit:- forgot to add great video, must try and make a radio someday.
No, as I'm relying on the crystal filter to attenuate any frequencies approx. 3kHz. Definitely do try and make a radio. You'd be surprised how little to you need to make an effective transceiver.
@@CharlieMorrisZL2CTM Great work Charlie. The wideband IF, (even tuned IF) has a lot of noise which is demodulated down to audio, on both sidebands. One can check just the IF sensitivity difference (w/o crystal filter) by doing a 10 dB S/N test, and then trying a simple filter at AF (eg LPF LC or active) The early Plessey designs using SL600/1600 were entirely wideband, and had to have an active LPF otherwise audio noise would have been horrendous (and so would sensitivity degradation)
