Use a frequency counter w/ signal strength instead of SWR??

Discussion in 'Wireless & RF Design' started by doug08, May 26, 2011.

  1. doug08

    Thread Starter Member

    Jan 30, 2011
    153
    2
    To tune an FM transmitter? I do not have an SWR/power meter. Why can't I just use my frequency counter with the signal strength meter, and also measure the amperage draw of the transmitter. That should work, correct?
     
  2. doug08

    Thread Starter Member

    Jan 30, 2011
    153
    2
    I tried the method I described(using an ammeter, and frequency counter with signal strength meter). I had total success. Yes, you do not have to use an SWR meter if you have a frequency counter with a RF signal strength meter, and an ammeter. Just connect the properly designed antenna for the amplifier/transmitter you are using, then connect the ammeter, then turn on your frequency counter about 8 feet away to start. Power up the transmitter/amplifier and monitor the current level and the transistor temperature. The transistors will get hot/very hot even though they have heat sinks. The 2n3866 has a maximum temperature rating of almost 400 degrees. I would estimate my transistor stays under 200, more like 140-160 degrees. I tried to keep my transistor temperature no hotter than where I can barely touch it. That being said, now you adjust all the trimmer capacitors until you get the highest signal strength/proper frequency on your meter. Try to adjust the signal strength to the highest level, while trying to find the lowest current draw possible for that high signal strength level. Once you find the highest RF strength/lowest current draw, then move the meter 15' away and repeat the procedure one last time to really get it tuned. My 1W amplifier works perfectly, and draws 60-70ma current.
     
  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287

    This should work fine. Just be sure to attenuate the signal into the frequency counter so that it doesn't saturate the AGC (if it has one) Generally these meters are more sensitive to changes with rather weak signals.

    Eric
     
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