I’ve been building and debugging a 2m LNA (low-noise amplifier) from this website:
http://www.ham-radio.com/n6ca/50MHz/50appnotes/U310.html
While it does work, it only gives me about 6-7dB of gain. This is far short of the 12-16dB claimed by the author and the datasheet, respectively. Once I figure out where my missing gain went, I’ll put it on a noise figure (NF) meter and see how close to 1-1.5dB NF it turned out to be.
Why, yes, that is a @Fred_Miller project box! 
It’s hard to tell what kind of caps you’ve got there, but if ceramic in particular are they rated 2-3x the operating voltage?
Could the RFC (Type 2 Toroid) proximity to the signal path be causing any issues? If it were me, I would place the choke under the board on the left to allow the ground plane to provide some shielding for it.
Also it looks like you have chained your ground between the left and right brackets. Specifically, I don’t see a ground connection directly from the pcb on the left to the green power pin?
The supply is +13.8 VDC, and I’ve never seen a ceramic cap (in the pF range) rated anywhere that low.
Good ideas, but the location of that choke nor its orientation seem to matter. Being a toroid, the magnetic field is constrained mostly inside of the [edit] core. Now the air-core inductors, those were a concern, prompting me to alight them at right angles to one another.
The ground is going through the coax braid, and all the metallic bits within this box have 0 ohms DC resistance to ground. I was also worried about power supply sag, but that turns out not to be the case.
I have seen SMD caps rated lower then that… I know you have at least one of those in there.
Not anymore… I broke it the other day. 
Yes, that was my concern. I was thinking that the RF itself might be introducing some feedback through the ground…
Feedback might be a problem, so I’m installing a PCB-material shield tonight to see if I can improve isolation between input and output. I’ll solder it upright along a diagonal line between the two inductors.
I would also include another ground connection from the green binding post to the pcb on the left. Can’t hurt…
So, tried in this order:
No joy. 
Strangely enough, LT-SPICE says this should work, and gives me the gain I’m looking for…
Bad transistor? Did you confirm the bias current?
Already replaced the U310 once, just in case I cooked or zapped it in my experimentation. I have a J310 that I could also try.
Bias current is set for ~15mA, closer to 12mA once the part heats up since my “current source” is a resistor.
I’d gladly test another unit if someone cared to build one and show me what I did wrong.
I’m going to set this one aside and build a different design using a common-drain design. This has the disadvantage of being slightly more noisy (higher NF).
A great paper on noise, and why an LNA is important when listening to signals close to the noise floor:
He clearly explains the concept behind the Friis Noise Formula.
Could the resistor be the problem?
What does spice predict as the power disapation?
I added a couple of parts to my latest Mouser order to let me build one. We will see how it does.
BTW, solved the problem with the audio amp for my SSB transceiver build. Basically I was an idiot.
I even changed that out… (I had to, since the bias was different between the two)
All three times, they were your standard carbon composite.
U310 is dropping ~10 volts at ~13mA on the current iteration, giving 130mW. The first one was getting a bit hot for my liking, so I put this one upside-down on the board, in contact with the copper ground plane. My PIR meter says the board isn’t getting much above 40C.
Based on your recommendation, I bought one of those fancy DE-5000 LCR meters. I’m impressed so far! The wound coils measure 103 nH, which is what I’d expect. Q factors anywhere from 20-34, depending on how close the windings are compressed together (probably due to varying capacitive coupling).
I would never use a carbon resistor in anything intended to be low-noise. Metal film might run you another ten cents, but worth it.
Yeh, its a great meter. Since it uses Kelvin measurement the probes can be upgraded…
