@freemo no, it's completely out of the blue!

@freemo I was confused earlier on by a minicircuits spec sheet for a 180 degree hybrid [1]. They only seem to sell three port varieties, I assume they fourth port is internally terminated or it isn't included somehow. Now the thing which confused me was that they referred to one of the ports as the SUM port. Hybrid couplers are often shown as 4 port devices with Sigma, Delta 1 and 2 ports. I would have thought the "SUM" port would be the sigma port, but then the output of the splitter would be two in-phase signals and it wouldn't really be much of a "180" degree" hybrid. Their SUM port must correspond to the Delta port, that is, the signal out of the "sum" port would be large if the inputs at ports 1 and 2 were entirely out of phase, I.e. the difference. It does behave this way, I tried it today, but my question is: why would they call it a "sum" port when if anything it's subtracting?! Am I alone in finding that confusing?

[1] - https://www.minicircuits.com/WebStore/dashboard.html?model=ZFSCJ-2-1

@AmpBenzScientist I need the passband to be at 202 MHz, with a few MHz of bandwidth. I'm no expert on filter technology, but this frequency seems a bit high for quartz and their passbands apparently tend to be very narrow. It is unfortunate for me, because they'd be ideal otherwise.

I need to maintain the phase between two signals and to filter at least one of them. At the moment I've just made a simple LC ladder and put an identical filter on both signals, so that hopefully when they drift, they drift together. The temperature stability of this approach doesn't seem terrible actually.

@freemo ah fair enough, I was looking out for a single resistor. Yes that works.

@freemo I can see you've got one on the reflected_SIG, but I can't see one on forward_SIG.

Half way through the magnetostatics post I promised a year ago. I've finished an introductory coax example and now I'm writing the intro theory for a cos(phi) magnet. I think it'll be ready in a week :) After that I see two options to progress: eigenmodes or time dependence.

If I go with the eigenmode, I can write an example for how the finite difference method works and talk about linear algebra methods. I haven't tried any time dependent problems in FEniCS yet, so that'll be a whole new area to learn.

Surprisingly, the blog is apparently getting a citation of some kind.

New post - Conformal Mapping Example, the Eccentric Coax

https://comphysblog.wordpress.com/2020/06/28/conformal-mapping-1/

This post is different from all my others. Rather than stepping through solving a problem with FEniCS, I step through solving a problem with the mathematical method of conformal mapping.

I introduce the method by solving the far easier problem of a pair of slanted parallel plates with a potential difference.

After that I get to the main point of the post: finding the characteristic impedance of a coaxial cable where the centre conductor isn't in the middle; where the cylinders are eccentric. Although the process has quite a lot of algebra, the final solution is simple and very usable.

I've really enjoyed doing this example, because I think it's a great demonstration of using analytical methods to solve a problem with strange boundaries. These days we'd probably just solve this kind of thing numerically, but the analytical solution gives insight and a formula that can be used over-and-over.

I'll add a numerical comparison in the coming days.

This blog is dedicated to physics and computing, with a current focus on solving electromagnetic problems using open source tools.

I work in particle beam diagnostics and am a PhD student studying the interaction of particle beams with their surroundings as well as the associated dynamics.

I'm Interested in anything related to particle accelerators, beam dynamics, detectors, electromagnetism and computing for science. I also enjoy tennis, fountain pens, fantasy & sci-fi books and board games.

Joined Aug 2018