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home brew transciever to newer amp????

Discussion in 'General Technical Questions and Answers' started by KB3HLK, Nov 13, 2009.

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  1. KB3HLK

    KB3HLK Ham Member QRZ Page

    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. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    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. K9STH

    K9STH Ham Member QRZ Page

    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. KB3HLK

    KB3HLK Ham Member QRZ Page

    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. WB3BEL

    WB3BEL Ham Member QRZ Page

    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. W8ZNX

    W8ZNX Subscriber QRZ Page

    Last edited: Nov 13, 2009
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    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 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.

    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.

    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.

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