2 Meter Linear Amplifier Question

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by W1CJG, Nov 18, 2015.

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  1. W1CJG

    W1CJG Ham Member QRZ Page

    I recently picked up a fair of RF concepts 2 meter linear amplifiers mostly for SSB and CW. Since I have 2 I was going to use the second amplifier for my FM dual band radio.

    The model is RF Concepts 2-317

    What I want to know is... if I have the amplifier and preamp OFF can I use 440 through it? and if so can I run full radio power which is more than what the normal drive level is?

    Just to make myself clear I am not trying to amplify a 440 signal with a 2 meter amp I am just wondering if the amplifier is in the off position will the circuitry be bypassed allowing me to run my radio as normal with no damage.

    NOTE: When the amp is off I have been able to use the 2 meter portion normally.

    I already tried doing a search and read the manual, I'll paste the link below for the manual with the schematic. I didn't understand the schematic well enough.


    Thanks and 73
    Chris W1CJG
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    I would say no.

    And if you forget it is on, Smoke may appear.

    A manual switch would be better.

    Good Luck.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd say "it's a bad idea" mostly because the signal path (in "BYPASS" mode, with the amp off but still in line with the antenna) is actually "tuned" for 2m. The signal from the rig runs through two sets of relay contacts, about a foot of microstrip, and some reactive compensation intentionally in place to tune out the wiring inductance -- and that compensation is set for 144-148 MHz, not any other band.

    You'll still hear signals through it, and you'll still be able to transmit through it, although SWR won't be good and there will be loss (attenuation) through the amp on BYPASS when used on 70cm.
  4. W1CJG

    W1CJG Ham Member QRZ Page

    Thanks for the responses,

    I think I am going to run an antenna switch and a small diplexer, one position of the switch will run from the transceiver to the 70cm input of the diplexer and the other switch position will go from the transceiver into the amplifier, then the amplifier output will go into the VHF input of the diplexer, and the common port of the diplexer will then go to my antenna.

    I could buy an antenna switch and I currently have a comet CF-416B "Duplexer" which is really nothing more than a high and low pass filter, with .25 dB attenuation high side and .15 dB low side.

    I guess I have to weigh if having .25 dB attenuation from the filter and .2 dB attenuation from the switch on 440 is worth running a linear/preamp on 2 meters. feedline is 20ft. of LMR400 so I'm looking at a "calculated" loss of a little over a dB.

    Of course this is all over thinking it but that's half the fun.
    Last edited: Nov 18, 2015
  5. KK4YWN

    KK4YWN Ham Member QRZ Page

    i would put that spare amp in the closet and sit on it until

    1. a good friend needs a ssb amp
    2. i popped my primary amp during a vhf contest or band opening (which is when all amps pop, by the way).

    FM rigs kick out good power for the mode. If you need an amp on fm: you have the wrong antenna.

    keep in mind the fact that vhf and higher are very attractive to anyone wanting to experiment with powerful antennas. the old guys talk about doing a few watts AM on 2m's in the way-back days. those guys put a lot of effort into excellent antenna systems, and we are wise to follow in their footsteps.

    best of luck with your weak-sig work. its a lot of fun.
  6. KM3F

    KM3F Ham Member QRZ Page

    If you want to tell for sure, put a flat Dummy load and 440 power meter on the amplifier output and see what you get.
    The amp does not even need to be powered.
    I would expect a significant thru loss but it will tell you for sure.
    Don't hurt to learn by running the test.
    Another way is use an antenna analyzer looking into the amp input and a flat load on the output.
    It will tell you what the match is at 440. If over 2 to 1 it's not good to try it with a radio.
    Good luck.

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