PIN Diode Question

Discussion in 'Homebrew and Kit Projects' started by VK4HAT, Feb 9, 2020.

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  1. VK4HAT

    VK4HAT Ham Member QRZ Page

    When using pin diodes as rf switches, what are the parameters i need to know to determine its suitability for a given rf wattage. Just reverse voltage? or forward current as well?

    I see the BA592 using in the baofang its 35v and 100ma. What am i missing here, those numbers do not even come close to 5watts?
  2. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    The surest way to fry a PIN diode is to use insufficient driving current from the DC control source. The diode must be driven hard enough so that it doesn't fall out of conduction during the negative RF cycle...that is where all the head is generated.
    The dissipation of the PIN diode and the RF design figures are two very different things.
  3. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    From the Digikey PIN diode application notes:
    Biasing the PIN diode

    The DC bias voltage needed to control the PIN diode's mode is a function of the diode as well as the RF signal level, temperature range, and other factors. This bias voltage must be decoupled from the RF signal and be stable, as any noise or ripple will affect the diode's operating point.

    When used in high-power situations, PIN diodes need a high bias-control voltage to minimize the cross-modulating effects of the voltage swing of the RF signal. For example, a 100 W RF signal has a peak-to-peak voltage of 200 V in a standard 50 Ω system. The control voltage must be greater than this and have sufficient headroom to prevent the RF signal's voltage from affecting the resistance of the diode and creating distortion.
  4. VK4HAT

    VK4HAT Ham Member QRZ Page

    Arhhh the 100ma is the bias current, not the current of the signal passing through yeah?

    Elecraft used 1n4007 in its tx rx switch, pretty sure there is no 200V supply line in that radio. So what am i missing here?
  5. W1VT

    W1VT Ham Member QRZ Page

  6. K8ERV

    K8ERV Ham Member QRZ Page

    Ok, how many know what P I N stands for?
    I do, cause I am perfect.

    TOM K8ERV Montrose Colo
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    To bias a PIN "off" better (to improve its RF isolation when not in forward conduction), pretty high reverse voltage can be used. I haven't studied what Elecraft does.

    PIN device selection is based on power handling and carrier lifetime. A lot of microwave PINs work great at VHF-UHF but won't work at 1.8 MHz (160m) worth a darn. Lower frequencies are a challenge for PINs and Elecraft uses 1N4007s but I wouldn't.:p Used properly, a PIN is a current controlled switch or modulator and not a rectifier, and shouldn't be rectifying anything.
  8. W1VT

    W1VT Ham Member QRZ Page

    I'm sure your customers can afford PIN diodes with a sufficiently long carrier lifetime.

    Did you know the Ten Tec Argonaut 515 used the UM9301 with a 4 uS carrier lifetime.
    May be the record for any commercially made rig for Amateurs.
    Mouser has them for $9 each with a 13 week factory lead time.
  9. KE5MC

    KE5MC Premium Subscriber QRZ Page

    From a Jun-2010 K3 schematic they are using BAP64-05. Several places it looks like they short-handed the nomenclature to 64-05 and a few 64-04 noted too. Without spending more time I'm not clear about the functionality where used other than KXV3 Transverter Interface and Receive Antenna Switching schematics. Might be a good starting point for the OP question. The one 1N4007 I notes was in the area of J10 and J11, 12VDC in and out control.
  10. W1VT

    W1VT Ham Member QRZ Page

    You typically want a lot of isolation to deal with transmit noise. And nasty things like a poorly controlled transmitter. But, the K3 has excellent control of the transmit circuitry, as evidenced by the lack of complaints when driving amplifiers like some other rigs. The isolation may not be needed since the circuitry will never be used with another transmitter, unlike the Elecraft amplifiers.
    N4FZ likes this.

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