Well the amplifier I soldered up last weekend that didn’t work has been fixed and seems to do what it’s supposed to. The soldering job is not going to win any awards for sure. But with the amount of rework I did, and my surface mount experience level, I think this is fine. It’s hard to tell here but the whole circuit (not the board) is smaller than the first two joints on my little finger. #HamRadio #AmateurRadio
Discussion
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@relistan Use flux. You can use too a hot air station to help with the ground plane. There're some pretty cheap.
@relistan BRAVO! Learning has occurred! Hair still present?
(Didn’t see a bypass cap at board PS leads attach point. Maybe behind leads?)
Achievement Unlocked: Working RF Amplifier!
@n8dmt also, nope, hair gone haha
@n8dmt I’m pretty happy this works. It’s not as good a design as the design I recently posted but I nearly had this one working and fixing it was an easier lift. So I’ll build the cascode version with better matching next weekend! Definitely learned stuff. Tons more to learn
@relistan Curious to see S11 and S22 if you have a NanoVNA or other capability. What was the gain? 3dB bandwidth? Thanks & 73
@n8dmt I don’t have a scope or sig gen. But I used my SI5351-based VFO to test gain with the TinySA and I tested S11 with the NanoVNA. I’m not sure how to test S22 because the power out is higher than the NanoVNA can take and if I pad it that will obviously mess up the measurement.
I tested gain through a 23dB pad I made so as not to run over the TinySA. Bandwidth I will try to test with the VFO/TinySA.
None of it is exactly what I got from Qucs-S but I expected that! #HamRadio #AmateurRadio
@relistan Discontinuities/jumps in Z-in (input impedance) or Z-out may be signs of instability. These may show up as straight lines in your response curves. Recommend narrow the sweep range (calibrating NanoVNA each time as needed) and looking closer around this frequency region.
Might try measuring amplifier throughput gain (S21) with NanoVNA. Calibrate with your 23 dB DIY pad in the through path, then add +15.5dB amplifier after pad (VNA P1, cable, pad, amp, cable VNA P2). Measure -7.5dB?
@relistan Think you can do quite a-bit with just the NanoVNA…
For output impedance (2-port shorthand S22), calibrate the NanoVNA for S11 (short open term), put your VNA calibration SMA-M termination on the the amplifier input SMA jack, then connect the VNA S11 test port to the output of the amplifier. (DC blocking cap is present in your circuit.)
For output impedance (2-port shorthand S22), calibrate the NanoVNA for S11 (short open term), put your VNA calibration SMA-M termination on the the amplifier input SMA jack, then connect the VNA S11 test port to the output of the amplifier. (DC blocking cap is present in your circuit.)
Alan W2AEW has a quite a few YouTube videos on making RF measurements.
https://www.youtube.com/user/w2aew
@n8dmt This is the VFO reading through the pad. The SI5351 puts out a square wave, so lots of harmonics. Note that this amp is supposed to cover all the ham bands up to 148MHz (well, 40m on down). Seems OK for that.
@n8dmt This is the reading with the amplifier running. About 15.5 dB of gain at 145MHz. Less than expected, but I wanted 15+ so this works! If you have better ideas how to measure I’d appreciate any suggestions.
@n8dmt thank you! And you spotted the same thing I noticed just after I posted it and was looking at it on my desk. It’s indeed missing! Good catch.
Actually the largest amount of work was getting those hand rolled air core inductors right. That took ages.
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