Measuring the output impedance of an amplifier does not require technical gear like a VNA, though that will make for a nice quick and accurate measurement. You can also do it using your multi meter and a scope. Here is how:
Connect the output of the amp to the swiper of a 10K pot or better yet, a decade resistor box.
And measure the resultant waveform on the scope.
Starting with the pot set to 10K ohm, adjust the pot until you have 50% of the amplitude of the signal.
Remove the pot from the circuit and measure its resistance, this value is equal to the output impedance of the amplifier.
You can then use a transformer turns calculator to determine the turns ratio for transformer for your circuit. Not hard now is it.
I have tried a few times to include a preamp in my DC Receiver project and each time I have had utter failure and that was using circuits that others have used and found to be reliable, so go figure. Rather tan trying to do the most ultra low noise amp, I figure i should just make a class A with a BJT and stick it in the circuit and see how it goes, it cannot be any worse than what I have managed previously, IE Failure.
So i have all the bits laid out ready to ugly build the hell out of this. The transistor is a 2n3866 RF transistor with a FT of over 500mhz, should be more than adequate for 40m HIHI.
Built and ready for testing.
Scope, signal source and power connected for smoke testing.
Feeding it with a very small 7mhz signal. The receiver is for 40m after all.
Success, 4v p-p with 50mv drive, now i just have to wire it into the receiver and see if it works.
On thing i manage to do well, is make a mess. Not so great on the cleaning up or being tidy and organized. But i got a little excited the other day and started to sort out all my stuff and make it into some sort of organized mess, where i can at least find things.
Starting with my component trays, I have them all stacked together now in the one location, the only thing i need to do is to add front lables so i know what is in each tray. Each tray has its own theme so its just a one word label that is needed, resistors, transistors, IC’s, Arduino etc.
So after getting all my componentry away and tidy, i had some bench space left over, and do i cleaned up and organized my work and test area of my bench. Things are nice and clean for now, I just need to find a place for my current project, the 3 boxes on the upper shelf and fill that gap with something nice like a spectrum analyser. HIHI.
So tonight i bout together one of 3 QRP Labs Si 5351a kits that I bought, not for WSPR use, but for future CW or SSB transmitter projects. The synth IC itself is awesome, 3 individually programmable square wave outputs. The kit went together ok, a couple od minor annoyances. The footprints used for the 2 transistors were wrong for the parts being used, and the spacings were kind of wring, there is so much more room on the board that it could have been spaced out better so the resistors did not sit under the cap of the transistors, and the SMA pads were about 1mm too short and required fiddling and spacing off the board before soldering, anyway, thats about all i can bitch about HIHI.
Parts laied out for install, 3 SMA connectors are not included in the kit.
Caps and voltage regulator installed.
Final product with headers and SMA connectors installed. Next i will make a board to mount this on, supply power to the 4 different 5v pins???? not sure if it needs 4 different voltage lines, but according to the pinout it does, will need to look into this more. Next job will be to code up some Arduino code to test it and then turn it into a VFO.
Its been a while since i have updated this space. I have been waiting on parts and kind of lost interest with my home brew endeavours for a bit, but i still find some time to tinker. I finally got the rest of the solar panels I had on order and have wired them up, 2 panels paralleled 4 pairs in series. Theoretically we should have 12v 8watts or 0.6amps.
So I got some sun today, being winter and 4pm in the late afternoon, to see 300ma peaking on a panel that should max out at 0.6amps is quite nice. With some sun intensity we should see close to the max being made, and certainly over 0.5 of an amp.
Unloaded voltage is about 13.8v, so everything is looking nice, now i just have to mount it all up on some plastic sheet i have, add some plugs to the wire, series diodes so the battery does not flow back into the panel and finally a volt meter and ammeter as I will be the charge controller and over volt protection for the AGM deep cycle,