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  1. audioguru2

    Re: can I change the output frequency of my fm transmitter?

    Adding a variable capacitor across the antenna will not change the frequency. The circuit probably uses a modern frequency synthesizer circuit with a quartz crystal and phase-locked-loop. Maybe the crystal can be replaced with one having a higher frequency. The existing crystal might be 6.2MHz...
  2. audioguru2

    Re: Wave Bubble?

    Do many countries still use only two frequency bands for cell phones? My cell phone uses many frequency bands and even hops over many frequencies using Spread Spectrum. This jammer would not cause jamming, just a little interference if it was very close.
  3. audioguru2

    Re: Wave Bubble?

    If somebody tracks you with a radio transmitter attached to your car then if you make a jammer they can also track the jammer. A jammer on a car will cause an awful lot of interference to a lot of people.
  4. audioguru2

    Re: dc power supply, 5v 5amp

    A PNP power transistor can be added to a 7805 or LM317 regulator to boost the output current. The simple circuit has no current-limiting. Here is the circuit:
  5. audioguru2

    FM Receiver help

    Please do not post the schematic way over at ImageShack who take all day to wake up. Instead, attach the schematic to your reply here at this website. You posted a tiny thumbnail photo over at ImageShack. Instead, please post a full size schematic. Your image is a fuzzy JPG file type. Instead...
  6. audioguru2

    FM Receiver help

    You posted the same pcb layout twice on a different website. You did not post the schematic. Why don't you attach the schematic here to your reply then we do not have to go over there?
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    It will be fine. The tolerance of a big electrolytic capacitor is wide so a 10000uf capacitor could be 8000uF to 15000uF.
  8. audioguru2

    Electronic Stethoscope 2

    Yes. Short the left and right channels together so both ears play in mono. The long jumper wires of a breadboard pickup all kinds of interference and might cause the circuit to oscillate. Use a compact stripboard layout or a compact pcb layout instead. Thanks, sparky
  9. audioguru2

    Re: coaxial cable and GHz frequency

    Your market is completely different to my electronic parts distributors who have everything. If you can't get 1 ohms then use 0.22, 0.33, 0.47, 1.5 or 2.2 ohms. They set the gain of the opamp. It depends on the supply voltage, the sensing resistor value and how high you want the output voltage...
  10. audioguru2

    Re: coaxial cable and GHz frequency

    OOPs, You are correct. The 10k resistor is not needed. :-[
  11. audioguru2

    white led

    My electricity is supplied by a hydro generator station between the largest lakes in the world (The Great Lakes) at Niagara Falls. The lakes never run out of water. There are two or three nuclear generating stations nearby. My electrical utility company plans for future growth.
  12. audioguru2

    help!

    Hi Jakoy, Welcome to our forum. ;D The very old transistors mic preamp has a fairly high distortion at high levels and the 1k resistor that powers the mic should be decoupled from the supply and should be 10k. The intercom circuit uses a noisy (hissss) LM386 power amp instead of a low noise...
  13. audioguru2

    white led

    It must be difficult to live in a tree. :o My home is on the ground and my electrical utility company keeps the electricity running for 99.999999% of the time. They also keep the voltage and frequency accurate. Of course it is not as hot here in summer as it is in your country but we still use...
  14. audioguru2

    Re: coaxial cable and GHz frequency

    Hi Eplanet, Maybe you are trying to sense the positive wire. But the LM358 can sense only the 0V wire. The LM358 must be a non-inverting amplifier unless you add a negative power supply to it. If the shield of the cable is 0V then I think it should be like this for a positive output from the...
  15. audioguru2

    Re: need help asa

    I don't know how you built it. It won't work on a breadboard and it won't work if the parts are too far apart.  It won't work if wires or a metal case are too close to the tuned circuits. Post a clear photo. I don't know if the pins on the transistors, voltage regulator or microphone are...
  16. audioguru2

    hydroxy gas power supply/separating oxygen and hydrogen from water

    The batteries say, "Do not short circuit" but you did with your current meter. The little one says, "7Ah at 20 hour rate", not 7A. It can supply 0.35A for 20 hours. Its max allowed charging current is 2.1A. The larger one says, "9Ah", not 9A. It does not say at what current. Its max allowed...
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    1) Pin 3's voltages are normal because U2 and the output transistors have a voltage gain of 3.07. 2) Pin 2's voltage without a load is way too low. If the output transistors are working properly then the output voltage would be pinned as high as it can go. When the output voltage is 1.5V without...
  18. audioguru2

    Re: need help asa

    If the output tuned circuit is peaked at 100MHz (the middle) then it still works pretty well at the ends. Then to tune the frequency you tune only the trimmer capacitor for the oscillator. Depending on the amount of stray capacitance in your parts layout it might not be able to tune to one end...
  19. audioguru2

    Are these 2 caps the same?

    Hi Stuee, The Oriental "green caps" are metalized plastic film (mylar or polyester). 103J is 0.01uF, 5% and is good. 103K is 0.01uF, 10% and is cheaper. I don't know what is the voltage rating of the cheap one.
  20. audioguru2

    Re: coaxial cable and GHz frequency

    An LM358 has inputs that still work properly when their voltage is at the negative supply voltage which could be 0V. So if you place a 1 ohm reistor in series with the 0V DC part of the power supply that feeds the LNB then the LM358 can sense it and amplify it.
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