Recent Posts

1

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

« Last post by pdenisowski on Today at 02:14:07 pm »

lets wait HAM fellows (names with numbers and who build their own radio) to chime in what they have to say

Depends on the kind of radio you're building (or operating)   In the United States, there are amateur allocations at 902 MHz and 1240 MHz, and some experimenters go even higher.

https://www.arrl.org/files/file/Regulatory/Band%20Chart/Band%20Chart%20-%2011X17%20Color.pdf

One of my commercially-produced radios (the Icom 9700) has 144, 440, and 1200 MHz,  Icom is also investigating making amateur transceivers for the 2.4 and 5.6 GHz ISM bands

https://www.icomjapan.com/api/download.php?page_id=66&fl=JTJGdXBsb2FkcyUyRmxwJTJGc2hmJTJGU0hGX3Byb2plY3Rfdm9sMV9lbmcucGRm

73, Paul, KO4LZ

2

Test Equipment / Re: Tek 2465 Horizontal Sweep Issue

« Last post by MarkL on Today at 02:13:25 pm »

On your probing of pin 18, the ramp will take as long as the sweep, approx. 10x the sweep setting to cover all 10 divisions.  If you're measuring with a voltmeter with the prescribed test settings, you'll never see the ramp because it's too fast.   One thing you could do is turn the sweep down to 0.5s/div.  The sweep across the screen will take about 5 seconds, and you should be able to see such a slowly changing ramp on a voltmeter.

Since you're getting a vertical deflection, you could also probe pin 18 with Ch 1, again at a slow sweep.  With this problem on your scope, what you should see is a dot slowly going up and then resetting, repeatedly.

What are you seeing on the back panel A GATE OUT?  A logic high here indicates that the A sweep has been triggered.

Does XY mode work?  Seems that it probably should given the other symptoms.

I would also try removing and gently cleaning the contacts with isopropyl on hybrids U500 (trigger) and U650 (display sequencer).  Don't mess with the nut on U800; it is prone to failure from mechanical stress.

3

Repair / Re: Desoldering advice

« Last post by fmashockie on Today at 02:12:59 pm »

After seeing the photos, the reason you are having so much trouble desoldering this relay is because look how beefy the traces are that it connects to.  You need a lot of heat to get those relay leads removed.  When I am working on boards like this (with thick power traces) I use a combination of hot air station and my iron.  I hold the iron on the lead to be desoldered, and hover the hot air over it.  This probably isn't good for the tip (I haven't seen any issues with my tips and I've done this fairly often), but this works.  Of course using a larger iron could possibly work.  But this method works fine with a Hakko FX-888 station and a decent hot-air station.  When I am dealing with multi-lead components like a relay that you can't just pull out one leg at a time, I also use solder wick to suck up the solder at each leg.  Again, you are only going to be able to do this with enough heat.  Use flux as well and continue to wet the wick with flux to get the solder to adhere to it and away from the leg to be desoldered.

The same goes for getting that relay back on the board.  You're going to need a lot of heat to get it soldered back on.  Same method works.  Add solder with the iron, then heat it up with both iron and hot air to get it to form a nice joint.  Obviously do this for as short a time you can to not overheat the component.

4

Metrology / Re: ESI RV622A Resistor Repair

« Last post by gmilliorn on Today at 02:12:16 pm »

It seems Manganin can be soldered, based on web searches plus comments from Edwin G. Pettis and
others such as here:
https://www.eevblog.com/forum/metrology/manganin-zeranin-enamelled-wire-availability/

From the close up of another resistor, the Manganin appears to be soldered while the lead is welded.
Even though they look quite different, I assume the end-caps must be Manganin as well, or else the
TCR would be affected?

There are cheap spot welders on ebay, used to weld batteries.  It might be interesting to try one, it's
an inexpensive experiment and would prevent desoldering the manganin wire connection, perhaps.

5

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

« Last post by madires on Today at 02:06:56 pm »

From an EU point of view (GDPR) the rules for telemetry are quite clear. Telemetry can't be forced upon the user, i.e. the application has to run also when users deny the collection of telemetry data. Users have to be informed about all the details (what, why, how long stored, and so on).

6

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

« Last post by radiolistener on Today at 02:04:09 pm »

Because you don’t, and that entire reply is proof of this. You just bark back, but never accept responsibility for mistakes, nor accept that others are correct. Look at the part of my sentence above that is in italics. (And which was in italics in the original.)

Your personal subjective opinion about persons is off-topic.

Your first reply in this thread, long after OP had listed the part numbers of the power supplies used, you suggested 1. using a motor-generator set, and 2. to consider switching to an SMPS inside.

Both of those suggestions are completely irrelevant and useless at that point in the discussion because it had already been established that it uses two universal-input SMPSs.

This shows you did NOT read the discussion before replying.

When I posted my first reply in this topic I didn't seen complete list of power supplies which are used on OP device. And correct me if I'm wrong, there is still no such list. Also I noted in the first OP post that his device power consumption is about 2300 Watt. And two PSU which he later provided for example is about 750-900 Watt in total, which is just about 40% of total device power consumption. So there is no way to decide if all of his PSU are compatible with all mains standards. I already explained it, but for some reason you're didn't read it.

I don't see why my post is completely irrelevant, the second part covers SMPS with universal input.

But even if all of their PSU are compatible with all mains standards, that is not enough to claim that medical device which uses these PSU will be compatible with all mains standards.


Regarding to the mains filter mentioned by IanB, it doesn't related with 50/60 Hz at all, their goal is to remove common mode currents in order to reduce EMI. I was talked about different filter which is used on device sensors ADC and in DSP stack to reject 50 or 60 Hz carrier from measured signal which appears due to interference from mains wires and due to leakage through PSU. It is software configured depends on used user environment. In medical device some signals working range may be very close to 50/60 Hz and even may cover that frequency and needs to be carefully processed with take into account the frequency of used mains line. Because interference level from mains frequency is pretty strong and it's presence can affect measurement results. This is why using PSU with universal input is not enough to decide that device is compatible with all mains standards.

7

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

« Last post by pdenisowski on Today at 02:01:51 pm »

if I understand correctly, for 5G it will be more easy than for 2G/3G/4G, because they using phased antenna array to rotate beam, so it will works like radar and allows to get more precise position of transmitter with triangulation, isn't it?

Steering the beam might allow for a rough determination of where in the sector the interference is coming from, but I'm not sure if any network providers who are using it for interference detection.  A more likely application is using it for interference avoidance (in the same way that "tilt" is used in pre-5G).

Incidentally, "triangulation" as a DF or interference-hunting methodology is, in my experience, both very overrated and very misunderstood.  Unless you are in a more or less reflection (multipath) free environment, it's very difficult to get good bearings: calculating the interception of those bearings is trivial, but junk bearings yield junk results. 

Since interference / jamming happens around (or at least is important around) people, this means most practical DF'ing is being done in urban and suburban environments where multipath can be an issue. 

For cellular network operators, they know from the base station stats (RSSI, e.g.) which sector or sectors are being affected, and in most cases you can simply drive (or walk) the sector until you get close and have to hunt on foot (where triangulation is completely useless).

Just wonder is it possible to use some kind of synchronized array of transmitters distributed all around the base stations and transmitted signals in that way so their interference signal at base station location gives false position of the transmitter or just spamming it with a bunch of virtual transmitter positions to make it hard to find which one is real? Are such kind of jammers are used in practice?

There are a lot of "creative" approaches to jamming, but high-end direction finding systems (like the ones we make) can usually still DF people trying to use "creative" techniques.  Generally speaking, for a jammer to be effective it has to be (a) loud, (b) wide, and (c) on, and all three of those things make jammers relatively easy to DF, regardless of how they are implemented.  A weak signal with a low duty cycle that's only a few kHz wide is harder to DF, but it's also not an effective jammer.

8

Microcontrollers / Has anyone used ASAN & MSAN, and relevance to embedded arm32

« Last post by peter-h on Today at 01:57:22 pm »

This came up on the MbedTLS mailing list, where somebody had some weird bug.

A suggestion was running the code with Asan
(https://github.com/google/sanitizers/wiki/AddressSanitizer) and Msan
(https://github.com/google/sanitizers/wiki/MemorySanitizer), both
natively available on Ubuntu.

But doesn't this require building the code for a "PC"?

In the case of MbedTLS one can indeed build a win32 version (and I do have that, done by the guy who did my MbedTLS implementation) although this was quite a lot of work, especially to use the same memory allocation strategy as the embedded target uses, which is quite important since you are processing external data (certificates of various sizes and with different hashes etc).

In my case I do not use the heap other than a one-off malloc for an optional feature which is never freed so fragmentation is impossible.

9

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

« Last post by shapirus on Today at 01:56:03 pm »

It's interesting. What's the rationale behind using a thyristor for something as simple as discharging the output cap? Why don't they use a resistor instead of it?

10

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

« Last post by Marco on Today at 01:52:37 pm »

Microsoft forcing telemetry on you is 'getting your panties in a twist'? That only seems innocuous compared to them not limiting it to the Store.

Could be worse, they could insert an online certificate check into your application (even though a certificate revocation list is easily possible and inherently superior for both privacy and security).