Recent Posts

1

Beginners / Re: Convert US standard 115V to International 230V

« Last post by TimFox on Today at 06:01:03 pm »

As a practical matter, most modern electronic equipment is designed to work equally well at 50 or 60 Hz.
The more likely problem is 100 vs 120 vs. 240 V.
Possible exceptions include "Sola transformers", which are less popular now, that depend directly on the frequency, or motors whose speed depends directly on frequency.

2

RF, Microwave, Ham Radio / Re: High bandwidth FM signal generation

« Last post by pdenisowski on Today at 05:59:24 pm »

Check out the DARPA program Computational Leverage Against Surveillance Systems or CLASS.

Interesting that (to me) at least some of this seems like "security through obfuscation."

1) Waveform Complexity uses advanced communications waveforms that are difficult to recover without knowledge and understanding of the signals itself; 2) Spatial Diversity uses distributed communications devices and the communication environment to disguise and dynamically vary the apparent location of the signal; 3) Interference Exploitation makes use of the clutter in the signal environment to make it difficult for an adversary to isolate a particular signal.

As for "dynamically varying the apparent location of the signal" - I'm not sure what that's supposed to mean.  The apparent location?  I'm guessing they mean having multiple, geographically distributed nodes all transmitting simultaneously on the same frequency, but there are also ways of DF'ing those kinds of signals as well.

https://www.rohde-schwarz.com/us/applications/super-resolution-df-method-application-card_56279-199552.html

3

Beginners / Re: Checking for noise in resistors

« Last post by TimFox on Today at 05:58:27 pm »

To understand resistor noise, I recommend reading Chapter 12 of https://pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Motchenbacher_Connelly/Low-noise_Electronic_Design.pdf , which is an update of the classic monograph by Motchenbacher and Fitchen: "Low-Noise Electronic Design", Wiley 1973.
I'm not aware of any equipment from that era specifically designed for measuring excess noise in resistors, but the books discuss test equipment designed to measure noise of amplifiers and semiconductors.
The fundamental difficulty is that the excess noise only rises above the unavoidable thermal noise in a resistor at relatively low frequencies, where measurements take a long time.
In some semiconductor devices, the "corner" frequency where excess noise exceeds thermal noise is much higher.

4

Security / Re: Microsoft repackages apps with a telemetry .NET wrapper

« Last post by radiolistener on Today at 05:58:19 pm »

What a myopic, hysterical, uninformed, and untrue claim.

There are definitely some uses for telemetry that are absolutely beneficial to the user: crash reports and usability research. Developers use crash reports to figure out what the most common application crashes are, so they can fix them.

We had telemetry system which was used for the system state monitoring, but as developer I don't remember even one case where I worked with the bug or crash report obtained with telemetry. All this is usually done with usual logging and issue tracker. I remember that we had some experimental telemetry to collect logs, but it was never used in production due to security reason.

I don't see telemetry use case for bug fix and crash report analysis, especially if its about not private system, but about collecting data all around the world. It just will be flooded with false positive and not relevant data for bug fixing.

As operating system user I don't need that someone research usability on my machine. Such an attempt to justify telemetry looks like grant unlimited permission to some random unknown student to allow him to access your private home at any time and examine your genitals while you sleep to research your usability...   

5

General Technical Chat / Re: ultra sonic transducers

« Last post by CatalinaWOW on Today at 05:55:48 pm »

I would not view the claim of 150 feet range by one commercial unit as reliable.  Unless you know a lot more about the company providing this unit, their history, user reviews and published data of results the claim must be treated as possibly false.  The field of ultrasonic control device is rife with charlatans.  Some may be good, solid providers, others are sincere but don't have a sound basis for their devices effectiveness and others are full on lying, with devices that don't even have measurable output. It is a good field for scammers as proof of defectiveness is hard to come by.

6

Beginners / Re: Convert US standard 115V to International 230V

« Last post by sanleontexas on Today at 05:55:15 pm »

The transformer really doesn't care if it's 50 or 60 Hz, it'll run fine either way. If it's a
50Hz transformer it'll actually run slightly cooler at 60Hz because it may have more
copper in it. And a SMPS will generally also run OK at either line frequency.
Unless there's some kind of frequency sampler circuit that wants to see a particular
line frequency(which would be rather odd), it's not worth the bother to design the
device for one or the other.

 

7

RF, Microwave, Ham Radio / Re: High bandwidth FM signal generation

« Last post by mawyatt on Today at 05:54:57 pm »

Check out the DARPA program Computational Leverage Against Surveillance Systems or CLASS.

https://www.darpa.mil/program/computational-leverage-against-surveillance-systems

We developed the computational chip over a decade ago for CLASS.

is there any public available detailed info about used approaches in this program?

Best check with DARPA directly, we can't disclose details on most things for obvious reasons.

One thing that we can disclose is the ability to create dynamic in real time and position elements for phased array beam forming. Think of this as a large physical area and number of moving in position and time phased array individual elements collective forming together in real time for massive beam forming capability

For example, imagine a large number of smart-phones moving around a large campus area and being elements in a vast synthetic aperture phased array able to dynamically beam form in real time while all the elements are moving around randomly!! You can imagine the enormous computational power required for this to work, yet all was condensed into a single ~1 Billion Device chip over a decade ago!!!

Best, 

8

RF, Microwave, Ham Radio / Re: High bandwidth FM signal generation

« Last post by pdenisowski on Today at 05:53:18 pm »

It is all about I want to create interference and come up with resilient communication solution for space-terrestrial based broadband communication. This involves a tiny band of frequencies over 400MHz bandwidth.

Most people who are trying to test reliability of a system over a non-ideal radio link will use AWGN (additive white Gaussian noise) or a single CW carrier with a given carrier/interferer ratio and at a given frequency offset from the "wanted" signal's center frequency.  The next step in realism is adding fading / multipath, defined in terms of "taps" with different multipath profiles.  And finally, if motion is involved, applying Doppler shift to the signal is also desirable.

Again, a properly-equipped vector signal generator (like our SMW200A) can add all of these impairs in a user-defined way to the baseband signal in realtime before up-converting it to RF.  There are some other manufacturers who do this at RF, but this is much less flexible and much less controllable.

Hope that helps!

9

Projects, Designs, and Technical Stuff / Re: Corrosion on DIP pins

« Last post by edavid on Today at 05:52:23 pm »

The insertion process can scrape the tin off the edges of the DIP pins, leaving the Kovar exposed and vulnerable to rust.

However, plastic DIP packages aren't hermetic, so there was already "humidity in the guts".  The ICs should keep working until the pins completely rust through.

10

Manufacturing & Assembly / Re: Advice on adding missing parts to an assembled board

« Last post by Kasper on Today at 05:51:57 pm »

You could make an extra layer for a custom stencil.  Copy the paste layer and add cutouts around the componets that JLC will place so the stencil won't hit them.

Apart from the massive difficulty this could cause during additional stenciling, which will depend on which parts are placed and which areas need additional paste...

If you order such stencil from JLC, make sure to specify that they use the stencil apertures as provided, else they will typically window pane the larger cutouts.

I didn't know they add windows.  Interesting.
Probably faster to cut the window panes but good to leave extra room for the stubs.

Not easy working with small squeeges to fit between components but probably easier and cheaper than what OP was considering: using small stencils.