I just "finished" packaging my BG7TBL "nose source" and am looking at the DC to 500 MHz response on my Instek MSO-2204EA. Both are limited. It's a 200 MHz DSO and the noise source is anything but flat.
Around 2007-2008 Franco Rota published a couple of articles in "VHF Communications" on the subject of diode noise sources. His 2nd article described the construction of small batch of diode noise sources given out to attendees of the 13th EME conference in Florence.
www.vhfcomm.co.uk/Noise%20diode.pdfhttps://www.rf-microwave.com/app/resources/uploads/diodes/VHFComm_NW303.pdfI'd like to organize replicating the EME source. That was built by milling out a piece of round aluminum bar for the enclosure. However, the only thing of importance is the dimensions of the cavity containing the circuitry. That is more easily produced by hydraulic forming with a rubber pad. One makes a male die of the required shape, places a sheet of aluminum on top and then applies pressure using a soft elastomeric pad and a hydraulic press. This is widely used for making airplane parts such as wing former ribs. During WWII a very large press, (20' x 80' ??) was used to make hundreds of parts in a single operation using dies made of micarta. A big advantage of this is the surface finish is much better than milling if the die is smooth.
I have a Clausing mill and a 20 ton press. So I can easily tool up and make enclosures at a cost of a few cents. I'd like someone with experience playing with DC to daylight to design a board and cavity dimensions based on Rota's articles. @svenskelektronik has expressed an interest in promoting OSHW. He operates a PCBA company, so he is in a position to manufacture the PCBs.
If enough people want one, I'd like to propose that a sample be sent to NIST for measurement and then circulated among the builders as a calibration reference.With a good design, well executed, we might even get lucky and find a NIST staff member who would take on a "Swiss Navy" project. In any case, spread over a number of participants, the cost per person should be quite nominal.
I also have a lot of experience writing DSP and other scientific software. So if the diode noise source includes flash memory for calibration constants which can be read via USB, applying the corrections would be very easy.