Recent Posts

81

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

« Last post by Zero999 on Today at 10:10:49 am »

Radiolistener, can you delete your posts?

Unfortunately, that would mean him admitting he's mistaken and going by his posting history, is something he appears to be unable to do.

82

Microcontrollers / Re: How to identify MCU by it's pinout?

« Last post by coromonadalix on Today at 10:10:37 am »

seems enhanced 8051 family ...  and  i think   STC does it too ??

83

General Technical Chat / Re: Is VAT number needed when ordering from Arrow USA?

« Last post by wraper on Today at 10:10:35 am »

So, is it legal to sell to the public without paying the VAT? Or just harder to get caught without the VAT number?

Pardon my ignorance, I have never been to the UK. As I said, I am curious.

Usually it is as long as business entity has small turnover so not required to be VAT registered, how small depends on jurisdiction.

84

Beginners / Re: PCB review and RF layout

« Last post by tszaboo on Today at 10:08:36 am »

No you don't match to your trace, because you make the trace 50 Ohm. If your trace is not 50 Ohm, you absolutely have to match to a trace which is any considerable length.

So you categorically deny the applicability of the feedline length trimming example?  Mind I don't mean as a practical basis, practically it's stupid, but on a basis of impedance. Impedance is easy to work with, and should be easy to prove or disprove.  Can you demonstrate with equations, Smith chart, etc. how it does not work?

It's like trying to use a 75 Ohm coax for a 50 ohm system, you get reflections. You might even need to open up the ground plane under a component, if the size of the component pad is larger than your 50 Ohm trace. Do you think they make these recommendations based on nothing? Nobody ever say that "Oh, don't worry about that component pad, it's shorter than quarter wavelength".

Pads..?  These... aren't 20GHz signals here. I'm not sure what you're getting at.

The old rules of thumb don't work in practice when talking about GHz signals, especially when GPS is involved with it's -120dBm signal strength.
Here is a measurement of a RF system, that I messed up by having just 600 femtofarad extra capacitance in the connector. That's just the effect of an extra 0.4mm * 4mm pad. Much shorter than the wavelength, that's ~40mm@4GHz.

I guess you forgot an attachment, oh well.

I did:
https://www.eevblog.com/forum/rf-microwave/help-me-improve-this-power-splitter/msg5272458/#msg5272458

Pads, yes they do matter, even at 1.5GHz.
https://infocenter.nordicsemi.com/pdf/nwp_033.pdf
Section 2.2.1
The pad size of GPS modules usually is quite large compared to the transmission line width. Same goes for an SMA connector pin size. Not to mention the SMA connector is a complicated 3D object, and in a lot of designs the CPW transmission line changes to a microstrip to the pin.
I just don't like this handwaving that "lambda/4 doesn't matter" when it absolutely does.

85

EEVblog Specific / Re: EEVblog #1181 - Car ECO OBD2 Fuel Saver SCAM

« Last post by elektryk on Today at 10:01:28 am »

That doesn't sound logical. Wouldn't better fuel economy automatically cause less emissions? Less fuel burned, less exhaust gas produced and all?

That's not only about CO2, after tuning NOx and PM emissions can be raised even when it is fuel economy tuning.

86

General Technical Chat / Re: Is VAT number needed when ordering from Arrow USA?

« Last post by jc101 on Today at 10:00:48 am »

If you are VAT registered you must, by law, charge VAT on any invoice. There are some exemptions and lower rates for specific things but those are quite limited.

As your VAT return contains costs for all purchases and sales it’s easy enough for the tax office to work out if your annual company return matches up. You can also be inspected at any time, no notice is required, though the norm is 7 days notice.
 
You don’t want to upset a VAT inspector.

87

Repair / Re: Rigol DP712 Output Shorted; Fuse? / I Screwed Up

« Last post by zanfar on Today at 10:00:20 am »

Sorry, can you elaborate?

I think you're saying to find a large diode connected to the output and replace it; is that correct?

If so, I'm curious how an overvoltage or overcurrent situation could blow something on a device rated for 50V/3A and how, in a blown state, that would short the output.

Thanks for the suggestion, regardless. I probably won't have time to crack the case until the weekend.

88

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

« Last post by shapirus on Today at 09:58:27 am »

In order to support both 50 Hz and 60 Hz standards, the device needs to be rated to work at least within frequency range from 48.5 Hz to 61.8 Hz. This is because it needs to support allowed mains frequency variation ±3%.

If it really supports all frequency range which include both standard, then he can use 1:2 voltage transformer. But it requires that device needs to be carefully checked and tested in order to comply with both frequency standards.

Once again, did you read the thread? It was figured out already that the device is using switching power supplies which support both AC voltage and frequency variants on the input.

89

Test Equipment / Re: Siglent SDS3000X HD and upgraded SDS1000X HD

« Last post by core on Today at 09:57:50 am »

But what kind of review do you expect Dave to do? In preparing a video, he cannot spend days and weeks to really dig into the subtleties of a device as powerful and complex as the 3000X HD. And his video format does not allow for the level of detail which Performa01 presented in his 800X HD thread -- nowhere near, in fact.

In this particular case I would like to know which FPGA has the SDS800 vs SDS1000 vs SDS3000 because they are all part of the same family, so as software they are similar, but as processing power I have no idea how different they are.

If the SDS1000 is just an SDS800 with a bigger screen, the price difference is not justified for many of us. About the SDS1000 we know what hardware it includes (user skander posted photos), but we don't know what FPGA and ADC converters the SDS800 has.

Same with the SDS3000. Unless it's significantly more powerful, faster than the SDS2000X HD, I have the same problem.

Also, it looks like the new SDS2000X HD, black, is coming.

Siglent is aiming higher than Rigol, and it would be nice to have more inside info (hardware) on these products. A review by Dave might help here.

Let's face it: The EEVblog videos are about entertainment, not about the in-depth assessment one would want to do before spending 5000€ and more. For professional customers, getting a demo unit would probably be the way to go. And for serious amateurs, at least in Europe, you can always buy a unit, test it for 2-4 weeks, and return it in case of major disappointments.

I'm not so sure about that.
Even though Dave doesn't always go into as much detail as we'd like, the work he does is VERY time consuming and the equipment he has access to for reviews is not available to all of us.

And the style he has covers a wide range of users. From beginners to advanced anyone can find useful and very useful information.

Unfortunately we can't find all the information in one place, we have to gather from several sources.

I don't like to order and then return the equipment. I prefer to have as much information as possible from the start.

And I wouldn't like to receive equipment already used as new.
If I don't like it, I'll sell it as second hand afterwards.

90

General Technical Chat / Re: Is VAT number needed when ordering from Arrow USA?

« Last post by EPAIII on Today at 09:52:58 am »

So, is it legal to sell to the public without paying the VAT? Or just harder to get caught without the VAT number?

Pardon my ignorance, I have never been to the UK. As I said, I am curious.