Taking Off The Training Wheels

Discussion in 'Homebrew and Kit Projects' started by VK4FFAB, Apr 18, 2017.

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  1. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    Lets not get carried away here; making statements like "The 1N4007 is actually a PIN diode. However, the lower-voltage siblings in the 1N400x family are not - use ONLY 1N4007."
    Are simply wrong and cannot be substantiated. This is the kind of misinformation that sets "hammy-hambone" apart from hombrewers, who are into amateur radio.
    Here is the datasheet...
    http://www.vishay.com/docs/88503/1n4001.pdf

    Truthfully I wouldn't caught dead using one of these as a PIN diode, maybe a varicap, even the range is limited and the linearity is garbage.

    Any diode will work to an extent as a pin diode.
    This diode family has too much junction capacitance to be all that useful as a PIN diode even at HF.
    There are better alternatives.

    Be careful of the advice that is out here on the Zed, some sources are more reliable than others.
     
  2. N2EY

    N2EY Subscriber QRZ Page

    To see how the 1N4007 PIN diode is actually used as an RF switch, look at various Elecraft designs such as the K2.

    As a dyed-in-the-wool homebrewer, with a 100% homebrew station.....I'd use a relay.
     
  3. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    You are kidding right, no reputable designer would use such a thing...
    That is laughable Jim.

    I guess you can't read datasheets.
     
  4. N2EY

    N2EY Subscriber QRZ Page

    Anyone can criticize, denigrate and insult others' designs.

    The real question is - what have the critics, denigrators and insulters actually designed and built?

    Not talking about repair or restoration. Not talking about some project designed by others. Talking about real with-ones-own-resources homebrewing.

    (crickets)
     
  5. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

  6. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    You are right anybody can, you would never see that done in any commercial gear, just hammy hambone gear.
     
  7. VK4FFAB

    VK4FFAB XML Subscriber QRZ Page

    Thanks for the suggestion Sue, I came to the same conclusion last night while doing my bed time reading and youtube watching. W2AEW has a couple of vids on diodes and switches and in one he showed a schematic for a shunt diode switch and the light bulb literally came on, i can do that and not have to change anything and pull any bleed over to ground. Its also what I am now planning to do.
     
    AF6LJ likes this.
  8. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    Since you are not talking about a bunch of RF (a Watt or more) that should work just fine.
     
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    For some clarification: The 1N4007 is designed as a rectifier and has no specified nor guaranteed minority carrier lifetime. It is whatever it is, and will vary by lot and manufacturer.

    I've been to probably every reputable rectifier factory in the world at one point or another (having worked for Motorola, Microsemi, Semtech, et al) and what I've found is the "lower voltage" 1N400x diodes are mostly fallouts from 1N4007s and didn't meet the breakdown voltage spec, which is tested automatically at a rate so fast you can't focus on the process (!) -- maybe several hundred per minute -- and a lot of the lower voltage rectifiers are pure junk.:p I suspect it's been decades since anyone actually set out to manufacture a 1N4001.

    If they did, they'd intentionally use lower resistivity material which would provide a lower BV, but also a somewhat lower VF -- which in low voltage circuits could be an advantage. But, they really don't.

    The "best" 1N4007s probably aren't very good in P-I-N applications as their minority carrier lifetime is simply too short. If they switch too quickly, they'll just rectify the signal and not attenuate it. That's why some very good microwave PINs which are wonderful don't work for 160 meter (1.8 MHz) applications -- although they might be fine at 7 MHz and above.

    "Real" PINs do have an intentional intrinsic layer diffused into them. Microsemi, when I was there, made PINs that would work well down to below 1 MHz -- maybe still do, I haven't been there in 20 years.:)
     
    N2EY, AF6LJ and VK4FFAB like this.
  10. KI6J

    KI6J Ham Member QRZ Page

    W7ZOI wrote several articles applying cheap rectifier diodes as T/R switches. W6JL's solid state T/R switch gives silky smooth QSK at 100 watts using 1N400x diodes.

    At QRP levels, the series-shunt jFET T/R switch popularized in KD1JV's designs can't be beat. It makes a very nice circuit to "modularize" as it is useful in audio muting as well. If you are not afraid of SMT, use the more robust BSS123 FETs.
     
    Last edited: Apr 19, 2017
    N2EY, DK7OB, AF6LJ and 1 other person like this.

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