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Wideband Loop Helper Build

wideband loop helper build

Overall, my wideband loop helper build was fast and simple. Everything was made easier with isolation milling a small PCB on my CNC.

As I described earlier, my objective was a two-channel switchable attenuator and medium wave filter to reduce or eliminate local broadcast overload during wideband reception. Since I had all of the through-hole parts on hand, I used these rather than surface mount components. Building a filter for lower frequencies is less critical, so I was not too worried about wiring and component leads.

My confidence in using my Genmitsu 3018 Pro CNC for circuit boards is growing. Not yet enough for tiny surface mount parts, but good enough for a basic THT circuit. I have pretty much standardized on 70 by 100 millimeter blank PCB stock purchased on eBay or Amazon. Cost is around $1 each. I have used both FR2 and FR4 stock, and find FR2 a bit easier to mill and cut.

As shown above right, I 3D printed a few plastic clamps to hold the boards on my CNC. Typically, I will mill one or two circuits on a board, and then cut them down later, if needed. For the wideband loop helper build I used the full size PCB. At the top right, you can see the copper plane with dual channels vertically, the attenuator on the left, and the filter on the right.

The trick is to make sure that my circuit traces and pads are well isolated from the copper ground plane. I cut 2 mm traces and pads. Since the CNC is well aligned, replacing the cutting bit with a drill lets you do both traces and component holes with one setup. Drilling precisely placed holes in way easier with a CNC than hand drilling. My holes are all 0.8 mm based on my previous careful measurement of the parts.

After you mill and drill the board, use a VOM to check for continuity along traces and isolation from the ground plane.

Wideband Loop Helper Build Wire and Solder

Mounting through-hold parts is easy as long as you bend the leads to fit properly. A small to medium size solder tip lets you solder without bridging. Again, once you have soldered, check all the connections with a VOM. My rule of thumb is to use as little solder as possible.

I cut down some Dupont header pins into singletons and used these for wiring the attenuator and filter circuits to the switches using jumpers. This makes everything easy to assemble or take apart. My project box is 3D printed in two parts, shielded with conductive paint, and held together with M2 nuts and threaded inserts.

Cheap double-pole double-throw (DPDT) On-On toggle switches work fine in this circuit. One side of the switch connects to the in and out headers for each of the filter and attenuation. The other side of the DPDT switch is used for bypass.

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