K4CHE GO-9 HF/MF Transmitter Project
     PA Tuning and RF Amp Meter

                    Chances are you will never see a very high RF amp meter indication while using your GO-9 HF Transmitter unless you have a very short or unusual antenna which exhibits a low radiation resistance or you have made a large error in tuning and placed the amp meter in the upper portion of a current loop.

The manual figure 32 provides typical input and RF outputs for several frequency ranges. Note that for 3000 kcs with a Antenna resistance of 4.1 ohms the RF Antenna current is 6.5 amps.                           Black arrows point to the columns.




             Shown above is a test jig for RF amp meters of the high current type( typically 5 to 10 amps). Most of my RF Amp Meters work on 60 cycles as well as the HF frequencies. Shown is a variac feeding a filament transformer which has the RF amp meter across the output.   I used my digital meter to monitor the current.(Not a true RMS meter but close enough for Government Work).
Be careful    -        -     make sure that the RF Amp Meter you are testing is of the a high current variety and not a very low current meter. Turn up the voltage slowly.



                          A coil exhibiting a low resistance can be fabricated easily. I used a piece of wood as an
insulator to keep the coil off of the cabinet. Turns are spread to prevent arcing.
         DANGER HIGH VOLTAGE can be present
even when in the Antenna Feed Switch is in the "Current" Position.


                    Low value variable potentiometers can also be used to provide a temporary load for testing.





                  A external RF meter can be put in series with the home made coil. In this case the meter in the photo was checked previously for accuracy and meter readings will be compared with the actual GO-9 meter on transmitter.
                                       DANGER HIGH VOLTAGE



              When tuning a low resistance be prepared to peak current with the ANT TUNING capacitor.
                           Don't forget to position the Antenna Feed switch to CURRENT.  


                   Red arrow points to the ANT TUNING capacitor(C330). The Antenna Feed switch(S304)
           feeds the RF meter and antenna.
                                additional comments needed on high and low impedance etc.



                  My favorite RF Amp meter test jig for the GO-9. A low wattage bulb in parallel with the coil load.


                            The low wattage bulb is "shunted" by the coil which prevents burning out the bulb, the coil and bulb assemble series feed the external meter connected to the antenna post. Keep your assembly well insulated from the cabinet top.


               A another test jig providing a low resistance load can be fabricated by attaching a 10 feet section of RG-58 with the end unterminated - - - Ground the shield andput the meter in series with the center conductor.


                 A binding post connector is handy. More on the connectors in the "Testing" Pages.


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