Noise Source Part 1 - Construction

I've heard of several local hams buying noise sources from China in recent days. I had read that they were based on this circuit found here and a quick look at the pictures in the listing supports this. I wondered how hard this could be?

I knew I had too many MAR03 mmics in the parts draw which I now never use. A quick Google and I came across an alternative approach here. So I quickly put a string of mmics into the pcb software and came up with a schematic and board as shown below:

 

I used whatever 1206 size inductors were in my parts bin for I1 to I4. I used a selection of values just in case this avoided some weird response in the output spectrum. One of the improvements I made was to put an attenuator on the output. It appears often overlooked but not all mmics have a good match to 50 ohms on the output port. The ERA5, used in the first example, is very good and would only see a small improvement with an attenuator. But since I didn't have one to hand I used a small amount of attenuation to bring this project closer to a 50 ohm output impedance.

I went up to the workshop and etching a board as follows:

I print an outline layer of the pcb and cut a piece of Cricut vinyl to suit.

I then remove the backing from the vinyl and print the layer onto it. It helps when you print the outline if you put a crease on the bottom corner of the paper to mark which way it goes back into the laser printer.

Then I iron this onto my pcb. Normally large black areas give me trouble because laser printers struggle to print dense large areas. So I tried something different today. I had just received some eBay sheets of gold foil transfer. In theory you put the grey side onto the toner and apply heat and pressure. It looks a bit rough but let's see what happens after etching.

I pulled the board out of the bubble bath and my initial concern was the patches of toner showing. Perhaps the toner density would prove too light and some etching of the groundplane areas would occur?

Only one way to know. I wiped the board with acetone to get this:

Apart from a few minor blemishes, particularly where the insulation tape crept up towards some tracks, everything looked good. The gold foil is definitely part of my standard procedure from know on.

So I fixed the minor issues and build this. Initial testing shows it works but I need to visit someone with better test gear than mine to verify this. As always if you need more details please ask.

I will report back soon on the testing.

Regards
Richard VK6TT