Search results

  1. E

    Op Amp Circuit Gain Does not Match LTSpice Simulation

    I created an amplifier in LTSpice as shown in the diagram and asc. file below. It is intended to accept a line level audio signal from a USB audio interface, and increase the voltage and current to drive a coil. The simulation indicates an output swing of about 0-9Vpp (blue trace). This is...
  2. E

    Series Resistor in Place of Line Distribution Transformer

    I have a 60W PA amp that specifies 166 Ohm impedance at 70V out. I know that a matching transformer is normally used at every speaker. But if I want to drive a single speaker (at distance) would it be possible for test purposes to simply insert a 200R 100W resistor in series for current...
  3. E

    Modify Hood Class A Amp for DC Path and Unipolar Output

    I have two Hood 1969 class A amplifier boards at hand. I would like to modify the signal path to DC coupled. The signal source is PC sound card line out (nom. 2Vpp). That is a bipolar signal so I need to adjust the DC input level to make the amp output unipolar. The purpose for this is to drive...
  4. E

    JFET "Amplifier". How Would This Work?

    I found this circuit hand drawn in my Dad's old notebook. There were no other notations except "amplifier". Can anyone tell me anything about its possible intended purpose, or how it functions electronically? Why are the JFET's wired in parallel, and what load resistance could this arrangement...
  5. E

    Unlicensed Radio That Will Transmit Continuously

    Does anyone know of an unlicensed type of radio that will transmit continuously? Most of the CB type seem to have a time limit controlled by the mic button. I want to broadcast a continuous signal for test purposes. It does not need to be audio modulated. Carrier frequency is not critical. What...
  6. E

    Opto Coupled Tunable Coil Circuit - Comments Please

    The circuit below is a thought exercise. The assumption is that an audio frequency signal is induced from an external source into the right-hand coil. At the same time is applied a 2Hz "gating" pulse at a voltage sufficient to power the LED. The two variable caps interactively tune the coil as...
  7. E

    Microprocessor Generation of Summed Sine Waves with Random LF Modulation

    I would like to program a micro to do the following: Generate five audio frequency sine waves at different frequencies and amplitudes Sum all the above sine waves into one signal Generate a pseudo-random low frequency waveform at a set amplitude Multiply the summed signal with the LF so the...
  8. E

    Series Connect 2 Plug Packs for Split Rail Supply

    I would like to place two 12VDC plug packs in series to create a split rail supply. I have done this successfully before but forgot where to place the blocking diodes so the SMPS' don't talk to each other. Can someone please refresh my memory? There may be all sorts of reasons this is not an...
  9. E

    Antenna Design to Capture Atmospheric E-field Gradient

    I would like to erect a tall antenna to tap into the Earth's atmospheric e-field potential relative to ground. Theoretically, this can be hundreds of volts per meter. The process is also known as "ion harvesting". What I had in mind was a 20 meter length of cable with pointed spurs or wire...
  10. E

    Using Detuned AM/FM Radio as Spectrum Analyzer Input

    I would like to use an inexpensive battery powered radio to capture and boost the entire AM/FM frequency band to display on a spectrum analyzer. Is this as simple as shorting out the variable tuning cap, and bypassing the demodulation stages, or would other component changes be required...
  11. E

    10X Multiplier-Prescaler for Frequencies Above 3GHz

    Does anyone know where I can purchase a 10X multiplier-prescaler for my R&S 3GHz spectrum analyzer? This is not for accurate quantitative readings but rather as a simple detector of the presence of RF signals up to 30GHz. I am hoping to spend less than $500. Maybe that puts it in the "kit"...
  12. E

    Circuitry to Randomize Audio Test Signal

    I have line level 120Hz sine wave that I want to randomize (not evenly modulate) in amplitude, frequency and/or phase by a factor of about 5-10%. Stated another way, I want to simulate a signal that is slightly unstable in as many ways as are practical, but still essentially a 100Hz...
  13. E

    Oscilloscope Probe at Audio Amplifier Output Causes HF Oscillation

    I built a John Hood 1969 type, single ended audio amplifier. It works fine into a speaker. But when I connect my Atten digital oscilloscope across the output, a 2Vpp 5MHz sine wave appears on the screen. It does not affect the audible sound quality. I tried swapping probes, channels, etc. to no...
  14. E

    Amplitude Modulation Using Op Amp Inputs

    The circuit below, once completed, is intended to modulate amplified noise from a 470uF cap with a CMOS generated ELF sine wave. As you can see, I am looking for a place to feed the ELF into the TLC272 stage to perform the AM function. Is this possible? If not, what is the simplest way of...
  15. E

    Can Batteries Exhibit Resonance at Particular Frequencies?

    For example, if I connect an alkaline D cell across a signal source, could one or more resonant "peaks" be detected upon an oscilloscope? If so, what would be the best test set up to demonstrate this effect on a fully charged cell? If such resonance does exist, what is its cause and how...
  16. E

    Experiments with Three-Plate "Capacitors". Center Plate Being a Coil

    I am investigating the interaction between capacitors and coils arranged in a stack. The configurations I intend to try are illustrated in the diagram below. There is an assumption that the input is bipolar, as if from the push-pull amplifier. The signal is any audio sine wave. Dielectric not...
  17. E

    How to Convert uT to w/m2

    Is there any way to make a mathematical conversion between watts per square meter to Teslas? For example, if a 10mW/m2 RF signal was measured at a given surface, how can the magnetic component of the signal be quantified in micro Teslas?
  18. E

    Continuous Play from WTV020 SD Card Audio Module

    I have a WTV020 SD card sound module loaded with a single 30 minute audio file that I would like to repeat-play continuously. Although the manual below describes a "loop" mode, I find the wording confusing. It sounds more like a resume after retriggering...
  19. E

    Load Driving from Transformer with Secondary Center Tap Earthed

    I am feeding an audio signal into the primary of an 8 ohm to 1K ohm microphone coupling transformer. The secondary is split, having a center tap. I would connect the center tap directly to earth so I can pull inverted signals off the active legs and have each drive a small resistive load to...
  20. E

    Explain QPSK and ODFM

    In the context of 4G, can someone please tell me, in as simple terms as possible, how a QPSK signal modulates the OFDM sub-carriers? What form does an OFDM "symbol" take? I have read a lot online, but cannot visualize what the transmitted signal would look like.
Top