Recent Posts

1

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!

2

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.

3

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.

4

Beginners / Re: Checking for noise in resistors

« Last post by CatalinaWOW on Today at 05:48:25 pm »

I think most of you are getting me wrong. I know about replacing the resistors for better ones, I already said that as well as I said that I'm just courious about the possibility to have a noise testing circuit. I'm sure there should be some designs out there. I'm aware of an old Heatkit tube signal tracer that can perform noise testing in components but such gear is almost impossible to get here in Europe, at least at a reasonable price.

Anyone know of some noise testing circuits out there? I'm sure there must be some around...

I haven't thought it all through, but I strongly believe you can accomplish what you want using the sound input of your computer.  This should offer adequate signal to noise for the measurement but is uncalibrated.  You can use FOSS software like Audacity to capture the data, or there are other open source programs more directly engineering oriented.  Calibration could be achieved by measuring a good film resistor and using the the calculated Boltzman noise to scale the measurement.  Read the Wikipedia article on Johnson-Nyquist noise for a quick run through of the calculation.

5

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by Fungus on Today at 05:46:40 pm »

I'd like to know what the Siglent does on a real AM waveform, too.

Feed in the 220MHz signal at 500MSamples/sec. but add some AM modulation and see if it reproduces it (eg. 16MHz modulator).

6

Microcontrollers / Re: How to create custom bootloader in esp8266

« Last post by tellurium on Today at 05:45:36 pm »

Well, yeah, but then it is quite unclear what "if button is pressed, enter the programming mode" means. The description goes about a simple bootloader that either boots a firmware, whatever it is, or "enters a programming mode" - which is, I believe, a built-in ROM bootloader in the programming mode. Note that OP mentions "OTA", but there  is nothing really about OTA in the description.


OP, you do not describe your task well enough, apparently because you don't understand it well enough. You need to refine your description.

7

Test Equipment / Re: Second bench PSU, am I thinking about this correctly?

« Last post by krby on Today at 05:44:47 pm »

If you have the space you could pick up something like an Agilent 6624A for very little money on ebay.
This particular unit has four isolated channels and they were used in automated test equipment setups.
They do not have banana plug sockets and the UI isn't great (LCD is hard to read) as they were meant to go into test rigs or system use and were usually remote controlled.
They are of high build quality, but are obsolete, so many installations have taken them out of service once Agilent (Keysight) stopped servicing them. All of this makes them a great deal.
If you don't feel like having to repair it from the get go, you should probably not get the absolute cheapest. Look for good vendor ratings.

Thanks for the reply! What would the advantage be to something like the 6624A vs a new (but cheap) linear supply? I guess better accuracy, regulation and ripple than a Korad? Since I'm new at this (and likely don't know what I'd be missing) I thought 1mV-3mV ripple is great for what I have planned. I really would like to be able to control it easily without a laptop or PC attached.

8

Microcontrollers / Re: How to create custom bootloader in esp8266

« Last post by kripton2035 on Today at 05:43:04 pm »

https://randomnerdtutorials.com/esp8266-ota-updates-with-arduino-ide-over-the-air/

9

Other Equipment & Products / How does the JBC (and clones) Soldering Station Sleep Mode Work?

« Last post by Astray on Today at 05:42:45 pm »

Hello,
I'm trying to get a better understanding of the JBC and Aixun T3A/T420 cartridge type soldering stations connections and how they work to put the soldering iron into the sleep mode while it's connected to its stand.

I remember reading a post (or maybe watched a video) about it but I've been unable to find it again even after searching the forum and googling. There was a breakdown of all the connections to the handle from the stand and the main station.

What is electrically happening when the outer metal part of the handle connects to the stand? What kind of voltage, current, and/or signal is it sending back to the main station?

I would like to know this information to make it easier to modify my soldering station and out of curiosity's sake too.

Thanks!

10

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

« Last post by Kean on Today at 05:42:35 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.