Recent content by Paul Colby

Yeah, starting from scratch with enough competence to actually do the design work is definitely the way to go. Also, cooling everything or most things is the way to go. There are definitely better ways than using cheap devices intended as general purpose radios for Hams. None of these are in...

This is a good question. I’ve done some experimenting separating the radios and shortening the cables from the clock generator. I’ve succeeded in reducing the common noise to the point that it can’t be used for syncing them. Every port is a two way street, noise comes in and noise definitely...

The total Johnson noise per Hz is ##4k_BTR##. For a perfectly matched network, only ##k_BTR## of it gets into the receiver. In this case it is ##1.38\times 10^{-23}\; 290\times 50 = -187 dBW/Hz## Did I miss something? Often not a vacuous question for me

Some 8 years ago I posted some experiments using 2 Software Defined Radios slaved to a common clock. The idea was measure small thermal noise by making correlation measurements between the IQ samples from each radio. This is a project that has kinda smoldered in the background where I've made...

I finally viewed the movie clip in post #15. It’s difficult to tell the magnet orientation from the video. I now understand and agree with the comments about the galvanometer response time. A scope would be better. If the magnet shown in #5 was employed, Neither of the two possible orientations...

For a normal bar magnet magnetized along its long dimension, yes. However, I suspect the north (or south) pole of the magnet shown in post #5 is face up in the picture with the south (or north) pole laying face down against the table. Dropping this type of magnet through the coil will produce...

Moving the magnet he has on the outside of the coil might also increase the voltage generated. Putting a magnetic metal core through the coil and sticking the magnet to one end would also give a lager signal.

The magnets of the type shown are common in both in variable reluctance motors and in linear motors. Invariably the magnetization vector is aligned through the short dimension of these magnets. When dropped through the coil as shown, I would expect the flux cut would very nearly cancel.

Magnetic field lines are closed loops. The field generated (and the corresponding forces resulting) depend on the path reluctance of these loops. It’s similar to circuit resistance and current flow. Magnetic materials are typically low reluctance, good flux conductors. Any air gap in the path...

Well, being serious about doing science and being interested in learning how things work by doing them really aren’t the same. I had serious doubts I could even detect the thermal noise from a 50 ohm terminator let alone a 10% change in said noise with the equipment on hand. So, this is an...

Before I get out a hacksaws and take multiple trips to the hardware store building an antenna, I thought I would first see if my Sdrplay RSPdx is even capable of detecting the small temperature changes needed to make observations of the 21cm hydrogen line. The radio has a LNA built in making...

Here’s a reference to some SDR evaluations. https://www.klofas.com/blog/2020/satnogs-station-and-minicircuits-lna-modifications/Evaluation_of_SDR_Boards-1.0.pdf They look at noise figures. I post this because the SDRs evaluated preform much better than I was expecting at 21cm. I also happen to...

I'd prefer to have some assurances that any bumps measured actually came in through the antenna feed and not some random interference or drift introduced by moving things like antennas and cables about. This paper definitely used 2 LNAs and a bandpass filter. LNAs can significantly reduce the...

Thanks. This will get a good read. Nice antenna design. I've dusted off my coaxial switch box which allows me to pragmatically switch between antenna and a 50ohm load. This should make differencing quite a bit easier. This should help reduce the effects of receiver drift. I also have boatloads...

There are much simpler tests I would definitely recommend first. Trying 0 buckets would top my list. These SDRs have a wealth of artifacts, noise sources, gain drift and other limitations that need to be understood first. They could well find this peak shows up anyway. It's quite typical that...