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  1. H

    Limit Current Maintain Voltage PSU output

    I want to maintain the output voltage of a power supply even when a circuit wants to pull more current than a defined upper limit (so I don't want to pull the voltage down due to over current). I'd like to supply 20 V to a circuit, while only allowing a maximum current draw of 150 mA. The...
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    Change Altium Library Location

    At the moment I'm using separate *PcbLib and *.SchLib files which are located within my working project folder. I'd like to put them in a central location (on the company server) and build on them, so that others can use them too and they become our central symbol and footprint libraries. When...
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    [SOLVED] Back EMF Diode Configuration

    I've seen two latching relay circuits with different back EMF diode protection configurations. I can understand how one circuit works, but I'm not sure how the other does. In the circuits below, I understand how "Circuit B" works, when the FET turns off the voltage on the connection to the...
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    Antenna Mounting within case

    For the antenna attached to this post, does the radiation pattern suggest that it can be mounted either way up in a plastic housing? I'm assuming that the ball like sphere of the pattern fully encases the antenna and isn't just out of the 'top' of it? So, if the antenna was to be shown in say...
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    Embedded Track Inductance

    Thanks for your replies FvM and Volker. Sonnet Lite looks really good, but the track I want to simulate isn't RF. It's the highlighted track below: The gate of the SCR will be driven by a micro and the trigger coil is a Tokyo Photoflash. There is concern that a track that is too long from...
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    Embedded Track Inductance

    I'm trying to determine the inductance of a track embedded within a PCB to simulate its affect. The layer stack info is below as I've found plenty of tools to determine trace impedance: The length of the track is 77 mm. How do I get from the stack info provided to an inductance that I could...
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    High voltage comparator with hysteresis

    Hi I want to use a comparator (powered off 3 V) to monitor a voltage supply going up to 25 V (where 3 V is the threshold trigger). I plan on using a potential divider to reduce the monitored voltage, such that when it's at 25 V the comparator will only 'see' 3 V. The trouble I'm having is...
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    Filter PCB Track Impedance

    I realise that for maximum power transfer, the input and output impedance of filters should match the impedance of whatever they're connected to (in this case 50 Ω in and out). My question is, should the PCB tracks between the Ls and Cs, that make up a complete filter, use track widths that...
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    Capacitor Discharge Time to Specific Voltage

    I would like to hold the logic level on pin 'D' of a D-type Latch high for 100 ns after the pulse driving it has gone to zero. The pulse will be from a NOT gate, 3 V and will be high for 0.5 ms (min). I was thinking of using a series R and C to ground to hold it above the logic threshold of 2...
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    Methods of Antenna Detection

    I've seen antenna detection done where a pull down resistor is built into the antenna to detect if an antenna is present or not. If say I was using an off the shelf dipole antenna (no built in resistor), what would be a good alternative way of being able to detect if that antenna was connected...
  11. H

    Directional Coupler Implementation

    I'm going to use an RF coupler to feed the transmit into the receive (in a TDM system) to measure power. I'm planning on using: https://www.minicircuits.com/pdfs/DCW-30-272+.pdf For the external termination resistor, should I use a 50 Ω resistor? I'm feeding 30 dBm @ 1.4 GHz into pin 1...
  12. H

    Differential Impedance LNA Match AD9361

    Danke FvM. That was an obvious and silly mistake on my part! :oops: Would you have any concerns about reducing the receive sensitivity by not having any matching?
  13. H

    Differential Impedance LNA Match AD9361

    I'm trying to match AD9361 differential RX at 1.3 GHz. I've got the S11 parameters for the RX LNA at 1.3 GHz: freq magS11 angS11 1300000000 0.453016055876785 -82.7105506901038 I'm matching this to the balanced input of a balun. Am I right...
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    [SOLVED] RF Accuracy from VCTCXO Specification

    Hi If the transceiver is transmitting at 433 MHz, with a reference VCTCXO of 30 MHz ±1 ppm, does that mean that the transmitted frequency accuracy will be: (433/30) * 1 ppm * 30 = ±433 Hz. So, the transmit frequency would be 433 MHz ±433 Hz? Not taking into account any tolerance of the...
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    [SOLVED] Crystal Oscillator Waveform

    Thanks for your responses guys. andre_teprom: I haven't grounded the body of the crystal. There wasn't any guidance to do this on the datasheet; is this best practice? How is this usually done? Using some kind of tab? Brian: Very good point! *sheepish grin*. I am running off USB (so not...
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    [SOLVED] Crystal Oscillator Waveform

    I've got a 32.768 kHz crystal running on a microprocessor and I'm concerned about the glitches I'm seeing on the waveform, should I be? The loading cap spec for the crystal is 12.5 pF (it's a CM8V from Golledge). I've loaded the crystal with 20 pF caps (tried to account for stray...

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