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Thread: home brew transciever to newer amp????

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  1. #1
    Join Date
    Dec 2005
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    Ocean City MD
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    Default home brew transciever to newer amp????

    I have a homade 40 meter rig used from an old CB I had laying around. is there any way to incorporate an TX line to engage the relay in my TEN TEC 425 amp? Do they make an RF (inline coax) sense to provide the keying voltage needed? Right now the rig is qrp at 2.9 measured peak watts. Would like to run it at 40 or so out of the amp.

  2. #2

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    Of course there is.

    Prior to amplifying its output I'd see if someone with a spectrum analyzer can confirm the output is clean enough to meet Part 97 spurious emission standards.

    But the rig itself obviously has a way to switch from receive to transmit, so there is an internal keying line. I'd just tap into that, and either buffer it with a transistor or possibly use it to key a relay which in turn would key the amp.

  3. #3

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    The best way will be to use something like a switch or relay with contacts that activate both the transmit function on the exciter and the amplifier. Then, with both units activated you can then key the transmitter (if CW) or, if SSB, talk into the microphone.

    Trying to sense r.f. is very "iffy" at best and really shouldn't be considered.

    Glen, K9STH

  4. #4
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    Ok, so sensing RF is not good, may I ask why? I know alot of the 10/11 meter amps are like this and even the old NCL 2000 has this option. I was looking at using a 2sc2999 and a relay and make an RF sense unit, but the internal keyline sounds fun...I might look into that.

    Whats typical voltage and current needed to key amplifiers? 9v-12v dc???

    I will take the rig into work and look at the IMD products before going further, but with the rig being monoband and using a passband filter, it should be ok.

  5. #5
    Join Date
    May 2005
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    One of the reasons RF switching is not very good is that it happens too late.

    The transmitter is already sending and then you decide to turn on the amplifier part way through the transmission. Lots of bad things can happen when you do this unless the equipment was designed to support it. Most are not they just sort of work...for a while.

    Think of this analogy. You get in your car in the morning and start it up. Then you stick the transmission in 1 and jam on the gas and let off the clutch. After that you decide to open the garage door.

  6. #6

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    [QUOTE=KB3HLK;1763970]Ok, so sensing RF is not good, may I ask why? I know alot of the 10/11 meter amps are like this and even the old NCL 2000 has this option.

    Whats typical voltage and current needed to key amplifiers? 9v-12v dc???

    QUOTE]

    Hello 3HLK

    National NCL-2000
    uses a regular inboard change over circuit
    close the circuit
    antenna relay switches

    nothing about rf sense change over
    in the National manual

    typical voltage needed for change over relay
    depends on the amp

    most modern amps you just open and close
    a low voltage dc line

    many older amps used outboard relay and pwr for that relay

    my Hallicrafters Loudenboomer uses a 117 volt AC
    outboard double Dow Key relay
    to use it with a modern xceiver
    use a interstage 12 volt dc relay

    so for the Loudenboomer
    need to supply the AC for the DowKey and DC
    voltage for interstage relay

    have a old collins rig that uses 48 volts dc
    on its relays

    in a big amp
    its more work to use RF sense switching
    if not done just right
    it will hot switch the antenna change over relay

    seeing as most ham radios have a provision for switching
    there is no reason to use rf sense change over

    in small amps like the Ten Tec 405 QRP amp
    rf switching is easy

    yours truly
    mac
    Last edited by W8ZNX; 11-13-2009 at 07:48 PM.

  7. #7

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    Quote Originally Posted by KB3HLK View Post
    Ok, so sensing RF is not good, may I ask why? I know alot of the 10/11 meter amps are like this and even the old NCL 2000 has this option.
    It's a lousy option for any mode except full-carrier AM or FM. For SSB, the T-R relay gets exercised a tremendous amount, and "hot keying" the amp is a big problem because RF is appearing at the amplifier input before the relay switches. The NCL-2000 absolutely does not have this option.


    I was looking at using a 2sc2999 and a relay and make an RF sense unit, but the internal keyline sounds fun...I might look into that.
    I wouldn't use RF sensing for CW or SSB at all, ever. Keyline is much more reliable and won't burn up the T-R relay in the amplifier.

    Whats typical voltage and current needed to key amplifiers? 9v-12v dc???
    The keying current source is always in the amplifier; you just provide a contact closure to ground. The Ten Tec is low voltage (12V) DC. But you don't provide that, the amp does. You just complete the circuit by grounding the keying contact at the amp's rear panel.

    I will take the rig into work and look at the IMD products before going further, but with the rig being monoband and using a passband filter, it should be ok.
    IMD has nothing to do with using passband filters; its distortion generated by modulation of an amplifier, and occurs within a few kHz of your operating frequency. There's no way to "filter" that out at the end of an amplifier.

    WB2WIK/6

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