Recent Posts

1

Manufacturing & Assembly / Re: Fellow LPKF equipment users?

« Last post by rsaxvc on Today at 01:16:16 am »

I've noticed the local harbor freight tools carries 20-pack of what appear to be compatible 38mm carbide drill bits, up to 1.1mm diameter, $7. No testing yet.

2

RF, Microwave, Ham Radio / Re: fake MPF102s from AliExpress

« Last post by radiolistener on Today at 01:09:51 am »

almost all transistors on aliexpress are fake. It can be branded but remarked other type, old repackaged, or just custom made with unknown parameters.

3

Projects, Designs, and Technical Stuff / Re: Vacuum Fluorescent Display Driver

« Last post by bostonman on Today at 01:04:10 am »

All the solder connections on the VFD looked good, however, I re-flowed them anyway including the ribbon cable.

FL1 and FL2 to ground is high impedance, 9.7ohms across the two pins FL pins, and approximately 1.3ohms across the two FL pins when the ribbon cable is connected to the unit. All other pins on the VFD to ground was (I believe) 4xx k. Not sure if these are good, but seems correct based on the FL lines being AC (most likely this is the resistance of the output transformer).

I found a previous message that states the DC/DC pins are off by one which makes sense when compared to the schematic.

Tomorrow I'll measure the SEG lines to see if they are going to approx. 38V, but what should the AC voltage be?

As for measuring the new HV518, obviously the VFD needs to be removed again, and this eliminates measuring voltages under a load since the VFD isn't connected. The other thing I'm keeping in mind is the start up sequence.

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Projects, Designs, and Technical Stuff / Re: Accurate sine wave in terms of amplitude

« Last post by PCB.Wiz on Today at 01:01:49 am »

But I do know today that I am iterating options how to generate sine wave - as clarified in the initial message including an example circuit.

Quadrature oscillator might be "the fresh idea I was looking for". Just that none of the first examples I tried to simulate on LTspice didn't work. Like this one:
Probably a simulation related issue - I need to analyze it further...

Whilst that circuit has two waveform at 90', it also has 3 RC elements, so it is less suited to a knob controlled oscillator.
When simulating such oscillators, you need to adjust the idealized gain, to account for real opamp effects.
You then find a trade off between oscillator startup time and clipping of one node when stable.

5

RF, Microwave, Ham Radio / ROHDE & SCHWARZ SMDU and SMDU Z1 test set owners!

« Last post by py1dkw@yahoo.com on Today at 12:51:33 am »

I had worked with this nice test set from 1984 to 1999 and now I could get the same unit here in Brazil. The R & S Support gave the available manuals, but my SMDU is changing its frequency in RF generator mode fast, but only in the lower band, the upper bands are ok and not out of lock. Does any owner of SMDU knows where I could start looking for the defective part? I had the SMDU Z1 unit restored and works fine. Many thanks, 73s Sam Rocha, PY1 DKW

6

Beginners / Re: How Current Limitation is happening in the circuit???

« Last post by ommsiva on Today at 12:49:19 am »

It is not an auxiliary coil that is used for deriving 5V for volt amp meter.


From the main transformer after full wave rectification,  I have used it.

I want to derive variable power supply up to 30V and current limiting adjustable up to 5 amp.

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Projects, Designs, and Technical Stuff / Re: Accurate sine wave in terms of amplitude

« Last post by moffy on Today at 12:47:10 am »

I am sure I have seen a design where a sampler was used to synchronously detect the peak of the sine wave.

Did that previously when our lab had to add a noise source to the dither signal of laser gyro, did a cycle by cycle comparison, a bit more complex but low ripple and delay.

8

RF, Microwave, Ham Radio / Re: HFH ROHDE & SCHWARZ RECEIVER LOOP antennas

« Last post by py1dkw@yahoo.com on Today at 12:46:03 am »

Generally the R & S comes with a graph in which the gain in each frequency is given, along with the cable loss discounted too. So HFH is a Field Streght Meter calibrated in dBuV. Very nice!

I would like to get in touch with SMDU and SMDU Z1 R &S owners, I will made a specific question, many thnaks, 73s py1DKW

9

Repair / Re: Tektronix DM501A repair

« Last post by xrunner on Today at 12:43:51 am »

One thing that ALL of the 500 series modules have in common is crappy switch contacts.

Concur. Clean all the switch contacts with appropriate cleaner.

10

Microcontrollers / Re: Divide clock by 3 on a ATF16V8B

« Last post by PCB.Wiz on Today at 12:35:09 am »

I don't know if this is possible on the ATF16V8B but this code will divide by 3 symmetrically only on the posedge of the clk
It's a cheat where you make a counter count to 3 and mux the output between 0, clk and 1 so I get the symmetrically from the clk input

That could be done, with some caveats.
The 16V8 has no CLK in the product term array, so you need to join 2 input pins.
Generating a CLK from an async MUX like that, exposes the risk of a runt pulse, in the handover from MUX=CLK to MUX='1'