[quote=“david.baker”]Here is a picture of the FlightAware ADSB filter.
http://imgur.com/a/SSkpT
[/quote]
Thank you, David! Very interesting!
Even at this price level, looks like they’re adjusting the inductors – when you look at the pic, you can see that the turns spacing on many of the inductors is uneven – that’s the result of someone taking a plastic (or even wood) tuning stick and spreading turns to adjust the inductance and the filter performance. Some inductors are untouched – compare turn spacing in L8 on the bottom part of the image to L9, L10 and you can see clearly where the turns have been spread out. That tweaking probably takes no more than 20 - 30 seconds per unit, if that.
(You want to or have to adjust the inductors as there are manufacturing tolerances in the capacitor values, probably a few percent, and also variations introduced by using FR4 as the substrate for the board – at 1 GHz, those tolerances add up and some parameters could swing as much as 10%. That leaves you with the inductors being the easiest (only) thing to adjust to tune up performance.)
Also interesting mix of automated and hand assembly – I’m guessing based on the look of the solder joints, but it makes sense that all the capacitors are surface mount, and some of the inductors on that side of the board look to have been reflow soldered as well, with the inductors on the bottom and of course the connector pins done by hand (and trimmed by hand, that’s another give-away). The duller, grey-ish joints are typical of lead-free reflow, where parts are loaded on to the board and run through an oven that takes the board (and its components) through a well defined heating profile which causes the solder paste to go molten, releasing the flux, and also pulling components into alignment on their pads by surface tension, then cooling with a really uniform look.
Other solder joints, such as the connector pins at the end, are more silver and don’t have the uniformity of a reflow connection. Looking at the top connection for L8, and the connection for L9, those look as if they might have been done by hand. I’ve done double-sided reflowed boards with surface mount components on both sides plenty of times. Never tried to reflow a board with through-hole components such as those inductors on both sides.
Thanks for an up close view of a successful product – and a good choice on vendor!
Anyone want to try their hand at designing a little beast such as this, and taking it into volume production? It’s a specialized business!
bob k6rtm