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Type: Posts; User: jiripolivka

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  1. Closed: Re: what is the mode for bend transmission line?

    Bends on a TEM line do not create other modes but cause reflections. To reduce reflections, various manuals recommend to increase bend radius or modify characteristic impedance .
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    Closed: Re: how does the ESD protection diodes work

    What theory? The input voltage is defined by the output voltage from a signal source having a source impedance say R. Then when the signal voltage exceeds Vcc (plus junction voltage, typically 0.7...
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    Closed: Re: how does the ESD protection diodes work

    The two-diode clamping circuit will not allow voltages exceeding the positive or negative lead to get to protected device input.
    What is missing is the signal-source resistance which will define a...
  4. Closed: Re: Why am I receiving big Gain differences

    One problem is that you did not mention if your anechoic chamber is specified for your frequeny of interest. Locating antennas so close as less than 10 wavelengths does introduce large errors due to...
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    Closed: Re: Input Impedance of Multiplier diode

    +13 dBm looks not enough for Class C operation. Simply make a one-stage amplifier with output tuned to the
    3rd harmonic, and adjust the operation point by base current for a max output. At 100/300...
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    Closed: Re: Input Impedance of Multiplier diode

    Good luck! For 100 to 300 MHz I would use a transistor multiplier, it is easy to build and run, has a gain instead of loss, and its input impedance is 50 Ohms.
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    Closed: Re: Input Impedance of Multiplier diode

    I would disagree. The I-V nonlinearity of a SRD generates a wide frequency spectrum like a spark gap, and if you filter only the third harmonic, the efficiency will be quite poor. This is why...
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    Closed: Re: Input Impedance of Multiplier diode

    If you use a standard VNA, it generates a low power for which a SRD multiplier would need an external DC bias to operate. Parametric SRD multipliers usually run at +17 dBm or more, and rectify their...
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    Closed: Re: Input Impedance of Multiplier diode

    If I may, I would add some practical notes.

    The PIN or SRD diode multipiers operate as parametric devices. I saw some attempts to calculate input impedance but it never worked. The truth is that...
  10. Closed: Re: Spectrum Analyzer and Channel Noise Estimation

    The "DC channel sensing", if it means that along with a RF signal you also send a DC voltage like +12 V, can be done using a "bias tee". This is a device with a capacitor in the RF line (between RF...
  11. Closed: Re: Spectrum Analyzer and Channel Noise Estimation

    First to start: Yes, you will damage the spectrum analyzer by applying 12 V DC to its RF input. Inside there is a precision RF attenuator with 50 Ohms nominal impedance. DC input will burn the first...
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    Closed: Re: Methods of Antenna Detection

    Depends on what point is desired. If you need to detect antenna connection to a device like a transmitter, use a SWR indicator or a reflectometer. A matched antenna will generate a low SWR response,...
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    Closed: Re: Cassegrain Reflector Fan Beam

    I am n o antenna expert but if you need a fan beam, you can use either prime-focus or Cassegrain or Gregory optics with an offset feed. This avoids any problems you mentioned.
  14. Closed: Re: When open-circuited stubs are preferred over short-circuited stubs?

    I do not agree. Please look in any choke flange of a waveguide, to see a shorted stub.
    If you leave a structure to radiate, it does not make a better short to ground.
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    Closed: Re: Transistors as diodes

    I have never heard about a fragile junction with holes. My noise dipole with eb diode of a SMD transistor I made 20 years ago was adjusted for 8 mA to make a strong noise at 11 GHz, and I use it to...
  16. Closed: Re: When open-circuited stubs are preferred over short-circuited stubs?

    Open-circuit stubs are problematic in that they tend to radiate. Short-circuit stubs are better, and you can use a short-circuit stub connected by a quarter-wave line to have the open-circuit stub...
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    Closed: Re: Transistors as diodes

    These e-b diodes in avalanche mode can be used as nice noise generators up to 13 GHz. A series resistor must be adjusted for an optimum noise output. Lower current, under 1 mA, allows to generate a...
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    Closed: Re: Books for learning radio engineering

    Try ARRL Radio Amateur¨s Handbook, any issue since say 1950. Includes basics up to the best communications technology.
  19. Closed: Re: S-parameters of waveguide without using VNA

    Without a VNA you can use a simple waveguide reflectometer. In addition to the oscilloscope you will have to use a waveguide detector and a calibrated attenuator.
    The refectometer consists of a...
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    Closed: Re: Noise Temperature Distribution

    This is a nice study but no real data, same as Balanis. You will have to try and see . Please let me know what you find by measurement.
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    Closed: Re: Noise Temperature Distribution

    I have an experience limited to microwaves, above 4 GHz. At 70 cm, with a helical antenna, I think the side lobes picking up the earth radiation would make the antenna noise higher than 50 K.
    Please...
  22. Closed: Re: Selective voltmeter wave analyzer project?

    The Swedish power indicator is a very rough device that can indicate short-wave band power on a log scale. For real measurement of e.g. harmonic content in a RF signal, one needs a spectrum analyzer...
  23. Closed: Re: Selective voltmeter wave analyzer project?

    As you do not indicate the required frequency range and RF bandwidth, I would prefer to make a simple spectrum analyzer instead. There are nice designs on the Web, some use old TV tuners, some...
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    Closed: Re: Noise Temperature Distribution

    Analyzing antennas for noise temperature output is not simple. At Ku-band, for instance, a good parabolic dish 3 m diameter generates typically 30 K when pointed to zenith. The reason are the side...
  25. Closed: Re: inverter theory - how can I bring the inveter to resonance ?

    Please see my suggestions to your other request on resonant inverter.
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