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  1. hfmobile

    MOS FETs as High Efficiency Rectifiers

    I am looking for cuircuit recommendations for high current MOS FETs with very low R(dson) used as high efficiency diodes with an extremely low forward voltage drop. As far as I remember, a fast single supply comparator was used to drive the MOS FET. But what about a fullwave rectifier bridge...
  2. hfmobile

    State of the art radiation detection

    What kind of radiation detectors are current state of the art concerning environmental detection of radio isotopes causing alpha, beta and gamma radioation these days? Are they still certain Geiger tubes or scintilation detectors or some more modern, maybe a semiconductor based scintilation...
  3. hfmobile

    Narrow band audio noise reduction with the SSM2000

    Is there anyone who has experience with narrow band audio noise reduction with the SSM2000? This IC was designed for noise reduction of HiFi-audio but my application is noise reduction in the range of 300Hz - 3000Hz. Is there, beside DSPs, an analog alternative for the SSM2000 or an alternative...
  4. hfmobile

    Audio Compressor with TDA4050B

    Dear Gunnar, yes, you are right. Certain old analog circuits ARE excellent and one is keeping the balls flying low :-) Andy
  5. hfmobile

    Audio Compressor with TDA4050B

    I have found what I was looking for. Not exactly HOW to design it but just a complete circuit, which is a good basis to experiment with: http://dk3hn.homepage.t-online.de/elek_fram.htm Thanks to all! Andy
  6. hfmobile

    Audio Compressor with TDA4050B

    I have the TDA4050B on hand, it's still available here and I have several of these on hand. As it is usable from DC up to 100kHz it should cope with audio frequencies right well. I will give it a try, I just need one working circuit and I will investigate the recommended ICs then (thank you for...
  7. hfmobile

    Audio Compressor with TDA4050B

    I think of evaluating a preamplifier with an automatic level control for audio frequecies (aka: audio compressor)in the range of 300-3000Hz to give a DSP a relatively constant input level. I came across the TDA4050B which is obsolete but still very cheap available. This IC has a dynamic range...
  8. hfmobile

    Subsurface (buried) or surface (on ground) HF-antennas

    Hi, I would like to find some information on subsurface (buried) or surface (on ground) HF-antennas. With regards Andy
  9. hfmobile

    Converting strange video composite signal

    Hi, we want to record a video signal from a video output of an elder HP-70206A spectrum analyzer. Its horizontal is 24kHz, its vertical frequency is 60Hz, with 1Vpp. Now we look for a scan converter which scans and converts this signal to a video signal compatible with a PAL standard composite...
  10. hfmobile

    DDRR antenna

    It is about the same as a small magnetic loop which is smaller than a quarterwave in circumfence and needs a special high voltage tuning capacitor. I recommend to build the halfwave version which is higher in efficiency, slightly larger diameter, slightly higher and a much wider bandwidth. The...
  11. hfmobile

    How to design a matcher-diplexer?

    Short antennas have a hígh impedance but if I have compensated all reactive parts of this impdance, the real part which is left is very small. This contains some resistive losses and the rdiation resistance. The latter is small because the antenna is short. I developed some LC-networks for...
  12. hfmobile

    Cellphone antenna with narrow beamwidth

    I think that DF-ing inside a building comes always with reflections. The antenna will be used when the the policemen are on their control-walks along the corridors (I suppose most times during the night). The problem with normal antennas with wide beamwidth was that the policemen were not able...
  13. hfmobile

    Cellphone antenna with narrow beamwidth

    I am looking for an antenna which is intendet to be used to detect illegal cellphones in jailhouses. The policeman is walking up and down the corridors with the antenna and a small specrum analyzer to look for rf-signals (900-2500MHz). To lower the risk of a wrong indication, the antenna should...
  14. hfmobile

    How to design a matcher-diplexer?

    I am forced to use this antenna which is a classic biconical shortwave vertical monopole antenna, originally specified to use for for 3.5-30MHz. I want (I should write "I am forced") to match it in the range of 2.0-30MHz or at least 2.0-28MHz by a broadband matching network. Usage of a classic...
  15. hfmobile

    How to design a matcher-diplexer?

    I need to use a biconical antenna for a broad frequency frequency range (ratio 1:15). I recorded the antennas impedance chart: for the high frequencies it is something next to 50Ohm but for the low frequencies it is something far off and very capacitive. The antenna is just too small. But I have...

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