Recent Posts

1

Projects, Designs, and Technical Stuff / Re: more modern version of tl494?

« Last post by xavier60 on Today at 11:06:04 am »

I read somewhere that newer TL494 ICs now have multiple pulse suppression to prevent noise causing unwanted toggling of the steering flip-flop. Has anyone confirmed this?

2

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

« Last post by gf on Today at 11:00:55 am »

The Rigol is applying the theory correctly and the Siglent can't possibly be doing an infinitely wide reconstruction, so... 

But you have the choice to implement either

• a truncated/windowed sinc filter with a n*sampe_rate...(1-n)*sample_rate transition band (symmetrical around 0.5*sample_rate),
• or an ordinary steep lowpass filter with a n*sampe_rate...0.5*sample_rate transition band,

where 0<n<0.5 (for example n=0.4).

Contrary to what you might intuitively believe, it's the latter which does what people here seem to expect when it comes to frequencies beyond the filter's reconstructability limit of n*sample_rate. But it requires more DSP resources.

3

Projects, Designs, and Technical Stuff / Re: role of optocoupler for biasing drain of amplifiers

« Last post by john23 on Today at 10:58:41 am »

Could you please draw the mosfet and amplifier with the devices ?
I am having trouble to imagine your words.

4

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

« Last post by Mechatrommer on Today at 10:53:50 am »

this is +1 imho in rigol, lets not forget, the 2 scopes discussed here got pros and cons.

Since the Siglent can into 2 Gsa/s, it could potentially be modded to support at least 800 MHz single-channel bandwidth, if there are no further limitations in digital signal processing and/or software. I don't recall anyone mentioning or trying this though.

i posted this earlier in this thread, some people said its very rare case. now we have 2 person asking for it so i'm not so rare, lets wait HAM fellows (names with numbers and who build their own radio) to chime in what they have to say, cheers.

5

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

« Last post by radiolistener on Today at 10:50:55 am »

I believe the OP is just not qualified or certified and should not be making this type of decisions.

There are too many unknown variables and the OP is, clearly, not qualified. A medical device sold professionally and for export and this is how it is being designed?  In America? Really? Nobody thinks there is something wrong in this scenario? Really?

Completely agree. I wanted to politely bring the topic to the point that this is not easy decision for medical devices, because there are too many pitfalls which is not visible for non medical devices staff, but it appears that discussion going into wrong direction and my attempt was failed. Unfortunately some users decided that since they see simple and easy solution, they can just ignore medical devices specific and advocate their solution as the best solution and fiercely rejecting and criticizing all arguments against.

6

Beginners / Re: Why are thermal jumpers so expensive?

« Last post by tooki on Today at 10:45:26 am »

AFAIK AlN ceramic is used for ceramic knifes, though the requitements on the material could be a little different.

Nope. They’re zirconia (zirconium dioxide).

7

Test Equipment / Fluke PM6304 serial interface card RS232

« Last post by minolta on Today at 10:45:14 am »

Hello,
who has downloaded firmware (EPROM dump 27C1001 - OTP) for serial interface card RS232 (label on my eprom is PM9549 v 2.2 , but probably could be used similar version too).
Has anybody it?
I have unit that can not receive command, sending is OK. I have tested all possible, now I need to check FW.

I can upload main firmware (from the main board) v. 1.8 (EPROM 27C512) if somebody needs this.

Thank you for help!
..

8

Beginners / Re: Why are thermal jumpers so expensive?

« Last post by tooki on Today at 10:44:16 am »

Somewhat similar and a possible replacement could be a high resistance SMD resistor, like this: https://www.digikey.de/de/products/detail/vishay-beyschlag-draloric-bc-components/MCA1206MD1005BP100/11196602.
Price is similar, too: 33 cents in 1000s.

Regards, Dieter

Nonsense.

If you look at the datasheet, those resistors are made on Al₂O₃ ceramic, which is a very different material (aluminum oxide) from aluminum nitride. Aluminum oxide ceramic has thermal conductivity 2-10 times worse than aluminum nitride. Sure, either is better than the FR-4 PCB substrate, but they aren’t substitutes for thermal jumpers.

9

Other Equipment & Products / Re: Any opinions on the Aixun T420D?

« Last post by Tor Björn on Today at 10:43:43 am »

The c115 handle is connected directly to the station?

Yes, T115A handle with modified plug (with added "stanby" pin #4 and wire soldered to it) is connected directly to the host. Other end of the added wire must be connected to mast with bracket for T115A handle.
Yellow pair must be disconnected from mast's nut because this pair is "standby" pin signal of cradle's plug that also connected with T245/210 bracket and work with other channel (T245A handle in my case).
Sorry for my English, I can't explain it in any more detail or more clearly. 
...

Also I'm impressed you were able to get the device for so cheap. The cheapest I could find before aliexpress coupons was $210 for a T420 with single C245 handle.
Did you purchase a C115 handle version (T405) (which I saw for around $170 on the store you mentioned) and then bought a separate C245 handle?

Astray,

I bought a T420 in the T245A configuration at a bestboard Store for $161.

T420 in the T245A configuration (with T245A handle included, but without specific mast with hangle bracket for T115A handle) have a regular price for $181.48 at this store. I used a $20 coupon at "anniversary sale". But similar coupones or promocodes you can get it very often. Aliexpress holds different sales almost every month.

I bought the hangle (mast) with suspension (bracket) for the T115A separately at the same store, $6.67 with coins per pair. The T115A handle cost $5.75.

The T115A handle i bought at the China DIYPHONE Store aslo with coins. Regular price was $8.19.








Additional cheapest T245 handle I bought for $3.03 with coins just to have a "donor's pin".

10

Power/Renewable Energy/EV's / Re: Power supply EMC document is erroneous?

« Last post by Faringdon on Today at 10:42:22 am »

 

Add an EMI ground or chassis ground and connect a Y cap, it's no longer a two-lead supply.

Thanks,  and if a metal chassis is added to a DCDC, (ie its enclosure or heatsink) then its a very good idea to always connect Y caps from DCDC circuit to that  chassis anyway, for noise mitigation issues.

I dont  know if there is anyway that would say "i have not connected my metal enclosure  to the DCDC inside it and therefore i dont need a common mode filter"
....this wouldnt happen, you would always connect  DCDC circuit (usually its ground)  to chassis with y caps.

Now if the DCDC's enclosure was entirely all plastic, then it would be a different story. However, the problem is that a DCDC does not  "know" whether it has an enclosure or not. If it exists somewhere on the planet earth, then the DCDC "thinks" that the surrounding earth is its enclosure.....and due to the earths enormous mass, it has low effective conductivity, and so even if inside a plastic enclosure, the DCDC needs a common mode choke in its 2 lead input. The Y caps will be provided by the stray Y caps.

Even if we have a 2 lead input DCDC, in a plastic  case, and  fed from a battery......neither battery or DCDC "knows" if it has a conductive enclosure or not.....they both think that the surrounding earth is their conductive enclosure, and so again, we have stray capacitance to the earth, (our  "third connection" and so we need the common mode filter.)

Here we see a common mode filter being designed for a DCDC

(3:10  onwards)