Re: {Collins} Need RCA SK3089 diode data (312B-4 mod)



I agree with Bill about the PEP wattmeter board.  I have added similar boards to a number of wattmeters.  Simply adding an electrolytic capacitor to the circuit will not work.  Analog meters have a problem with instantaneous signals because of the mass of the meter movement.  So, when you have a voice peak, it will not fully indicate what the true reading is.  Each meter and voice varies.  And, if you attempt to turn the gain up high enough so that the meter peak will read the same as it did in cw/tune mode, you will overdrive the amplifier and often splatter.  

Some manuals specify that a normal voice may indicate 50% or some other value of full scale during normal voice operation.  But, that is just a wild guess.  Many years ago I put a scope on the output and soon noted that I reached full output when the meter read about 25%.  So, the gain was turned down.  

Adding a capacitor to the meter does not solve the problem.  It will store the charge, but it will not charge instanteously, so you are still likely to turn the gain up too high.  

A peak reading wattmeter circuit is normally a high impedance amplifier that does not load the input, but then is able to hold the peak value.  It works like an s-meter in a good avc system.  

Using an analog output meter without a true peak reading circuit must be interpreted by the operator who understands what information the meter is giving.  

73,  Colin  K7FM



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