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Beginner PCB review request - RF Amp

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cadr:

--- Quote from: T3sl4co1l on May 31, 2021, 05:38:55 pm ---Strays are generally trace length.  At high frequencies, a trace above a ground plane (or surrounded by it, or both -- what you have is known as coplanar waveguide with ground (CPWG)) is a transmission line, which has characteristic impedance and velocity.  Signals don't move instantaneously, after all.

Which is one of the conceits of schematic representation: there is no way to indicate length, it's assumed zero-length -- pointlike -- or equivalently, assuming infinite speed of light.  So it's easy to get tripped up between schematic and layout, when those dimensions matter to the circuit.

At low frequencies, we can reduce transmission lines to equivalent series inductance and shunt capacitance.  For traces around 100 ohms, these are around 1 nH/mm and 0.03 pF/mm.

It doesn't sound like much, but it adds up, and circuits don't have to go much faster than this to really feel it.  Most CMOS logic parts (gates, MCUs, etc.) are fast enough to have wave / transmission line effects on traces merely 10s of cm long.

For example, what about the -- uhh, none of these nets are named so I have to describe them by component members, don't I --  R1, R2, C1, C5, Q1: this net makes a fork between Q1 and C5, when they could all just be in a row, C1-R1-R2-C5-Q1, packing everything closer and about halving the total trace length.  R4 should be right beside Q1, it's a local feedback path, delaying that is a bad idea in general.  Why not butt Q1-Q3 all together?  They share many connections, they don't need all those ugly corners and extra length between them.  I don't even know how Q2-E to Q3-B jogs up above the pads, it's like they were routed to make the signal follow the component centerline, not the pad centerline.  Which seemingly intentionally blocks off ground fill between pads, necessitating vias to connect it back up.

Oh, what's up with the different size components, 0805s and 1206s is it?  Just now realizing they're different...  All 0805 or 0603 should pretty much do for everything here... you might not like 0603 so much for beginning hand soldering if that's what you'll be doing, but 0805 I would say is fair game.  If your hands are a bit shaky or your vision not so sharp, 1206 might be more comfortable.  Or you can do everything through-hole, this circuit won't care.

Tim

--- End quote ---

Got it.  Thanks!  I'll take a look at that.

The different size components - I wanted to use the JLCPCB assembly service, and the ones that are different sizes were probably not available as "basic" parts.  Though I found the process of finding parts through their UI very difficult (someone linked me a github project that made it much easier) so it could be that they were available and I just didn't see them.

Thank you again for the feedback and advice.  I am learning a ton.

cadr:
Thank you everyone!  I got the boards in, and they look good and seem to work.  Will hopefully be able to do more measurements over the next week, but am super excited they are actually amplifying :)

Have pictures, etc here: http://kc9dlm.blogspot.com/2021/06/babys-first-pcb.html

Mattylad:
A bit late to the party and I'm glad it works however:

When you make your next board or modify this one, try and make your reference designators more readable.
I.E. All reading from lefty to right or bottom to top so that they can be read from one direction.
Also ensure that no refs are over copper or other refs nor under components.

I suspect that now it's made BIDIRECTIONAL probably has a screw head over the "AL"  :)

cadr:

--- Quote from: Mattylad on June 10, 2021, 10:10:42 pm ---A bit late to the party and I'm glad it works however:

When you make your next board or modify this one, try and make your reference designators more readable.
I.E. All reading from lefty to right or bottom to top so that they can be read from one direction.
Also ensure that no refs are over copper or other refs nor under components.

I suspect that now it's made BIDIRECTIONAL probably has a screw head over the "AL"  :)

--- End quote ---

yeah, I was having trouble with that in the EasyEDA tool, and I really needed to stop fiddling with it and just order it :)
And if I had to actually assemble them myself (as opposed to having JLCPCB do it) I definitely would have.

But, yes, I agree that would make it much better.  Thanks!

dunkemhigh:
A minor thing (but many small things can add up) is the ground pads. Generally you try to keep things consistent (i.e. pin 1 always this way, diodes always that orientation, etc) so when someone is whizzing through thinking about last night's TV they don't miss the single item that is different to all the others. On this board, the sig/gnd pair are inconsistent, sometimes the gnd is on the left, sometimes right. The through connections could be forgiven (signal always this side of board, ground that side), but then the top and bottom pair don't match that scheme.

Given the single-sided constraint it may not be practical to make them consistent, but always worth keeping at the back of your mind when you're doing this stuff.

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