2 Meter & 450mHz Brick Amplifiers- Short take

Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, Jun 23, 2019.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I find about the same. If you have a good receiver on 222 MHz, a preamp in the shack does nothing except raise signals and noise all the same 20 dB. It would take a pretty bad receiver to be helped by an in-shack preamp on this band. But...some receivers may actually be that bad!

    Nothing against preamps, but the SS brick amps that include them all seem to use miniature, sealed relays to switch them in and out of line (they use those for T/R changeover also) and the damned things fail. It's counterintuitive but the "receive" contacts are the ones that frequently fail (not the "transmit" contacts that handle the amp's output power), probably because they never conduct any current (well, maybe a microamp or something, but not enough to prevent surface oxidation). First thing I do with any of these amps that include a preamp is open it up and bypass the preamp and its relay system entirely with a short length of small coax.:)
     
  2. AA7QQ

    AA7QQ Ham Member QRZ Page

    At work, we have come to use biforcated (sp) contacts for small signals. Much more dependable.

    Ed
     
    KD2ACO likes this.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Frankly, PIN diodes could be a thousand times more reliable.

    This one can handle 55W forward power mounted on an ordinary FR4 circuit board; with a heat conductive board providing thermal sinking, 150W is pretty easy -- in quantity, this device costs $1 each.

    There are better diodes, too, of course, but they cost a bit more.
     
  4. AA7QQ

    AA7QQ Ham Member QRZ Page

    They would not work in this application. It's for the brake on winches. 105VDC @6.3 amps. THe small signal part is to signal the PLC that the brake is disengaged. It all needs to be contained in one relay/contactor (Actually, 2 in parallel for failureproofing).

    Ed
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    What? I'm remote now and can't check the link quickly, but I meant to link a PIN diode rated for RF switching; it had a carrier lifetime, forward resistance, off resistance, power rating, etc. published.

    Lots of those in SMD form are available today in the $1-$2 range that will handle substantial power at VHF if there's a way to get the heat out of them; their on resistance is so low that at 100W forward power they'll only dissipate 1W or so, so there's not a great deal of heat there.
     
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    The link looks great!
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I just re-checked my link and have no idea what you're writing about above.

    The link goes to the spec sheet of an RF characterized PIN diode.
     
  8. KX0Z

    KX0Z Ham Member QRZ Page

    No mention of Tokyo Hy-Power?
     
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    They're out of business, but when they were in business they did make some fine VHF-UHF amps.
     
  10. N8FVJ

    N8FVJ Ham Member QRZ Page

    Tokyo Hy Power brick amps are rare. I never see them for sale.
     

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