Re: LED Power Output Indicator #ubitx

Howard Fidel

Seems like you should have left the 2.2 K resistor. Here is the analysis:
10 watts into 50 ohms requires 22.3 Vrms. You have to diode drops in series, so we could say that you have roughly 20V rms across the resistor. 20/2.2K is 9 ma, which is a nice diode current. The actual current will be less, we need to calculate the droop on the capacitor for the 1/2 cycle that current is not flowing, which is small for this load and capacitance, dV=.009  275 x 10**-9/.01 x 10**-6 = .25 Vm which we can ignore. Most LEDs can go up to 15 ma at least, so depending on your LED, you may want a smaller resistor.


On 7/3/2018 9:41 PM, Lee wrote:
I ran across this when looking for an transmit indicator for my Small Wonder Lab PSK31.  The original resistor was 2.2K but our radios put out more than double so I changed the resistor to 5.6K.   Maybe someone with more electronic knowledge than me has better suggestions.   It lights up bright and solid for CW and you an watch your modulation on SSB.   I can really see the difference when I switch in my SSM2167 module.
Lee - N9LO  "I Void Warranties"


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