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LED Power Output Indicator #ubitx

Lee
 

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"


 

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.

Howard


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"


 


Lee
 

Wow, I knew I would get a great explanation.  Thank you.   I guess I got lucky.  I used a clear red LED and it is nice and bright and fun to watch.
--
Lee - N9LO  "I Void Warranties"

 

Jerry Gaffke
 

I'd recommend placing it before the transmit LPF, not at the antenna port.
The diodes will create a bit of harmonic content that the LPF's can remove for us.

I think you could remove the lower 1n4148 and get the same performance.
Then it's just a diode detector, like found in some AM radios.
The LED should start turning on (in a dark room) at 3.0+0.6 = 3.6v peak.
That's 3.6*0.707 * 3.6*0.707 / 50ohms  = 3.6*3.6/100 = 130mW

I don't think the lower left 1n4148 adds anything except perhaps clipping the low going
tip of the RF more or less the same as the high going tips get clipped by the other diode.
This might reduce some of the harmonic content, but the LPF would do a much better job. 

If the 5.6k series resistor also had a 0.01uF cap in series with it, then you should
get double the DC voltage to the LED making this usable with lower power rigs. 
The LED would start turning on at around 3+0.6+0.6 = 4.2 volts pk-pk, or 2.1v peak, or 2.1*2.1/100=44mW.
A low going RF tip will cause the lower-left 1n4148 to conduct, charging up that
new series cap.  So the voltage into the second 1n4148 will be an AC waveform
that rides up on top of ground instead of being centered on ground.

Jerry



That lower left 1n4148 doesn't really do anything except maybe clip
the low going peaks in a manner almost symmetrical with the high going peaks 
that get clipped by the other 1n4148.


On Tue, Jul 3, 2018 at 06:41 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.

R. E. Klaus
 

Doesn't the 2 diodes and the cap form a rudimentary voltage doubler similar to those used in old AC/DC radios?

Jerry Gaffke
 

Simple as it is, could be I don't fully understand the circuit.
But I don't think you get a voltage doubler unless you add the extra cap in series with the 5.6k resistor
as suggested in the last paragraph of my previous post  (ignore the garbage after my signature).

In my calculations, I'm assuming an LED forward voltage of 3.0 volts.
That's typical of the very bright white light LED's, 2 volts is more typical of a little red LED.
But the extra volt is probably needed to see anything at all anyway, given the 5.6k resistor
and that diode conduction occurs only on RF tips.   Even in a very dark room.
But should be reasonably bright with 5 or 10 watts.

Jerry


On Tue, Jul 3, 2018 at 08:25 pm, R. E. Klaus wrote:
Doesn't the 2 diodes and the cap form a rudimentary voltage doubler similar to those used in old AC/DC radios?

 

 

Dennis Yancey <bigbluedry@...>
 

Simple circuit. Makes you wonder if you can somehow put a VU meter in there and have a relative power over 8 or 10 LEDs

Lee
 

Please don't assume a 3.0 volt LED and reasonable brightness. As I already stated,

I used a clear red LED and it is nice and bright and fun to watch.

I have received all the information I was looking for.   Thank you.

It works great just the way it is.  "If it aint broke, don't fix it."
--
Lee - N9LO  "I Void Warranties"

 

Howard Fidel
 

It isn't a voltage doubler. You need a second cap for a doubler. The Diode to ground keeps the load symmetrical (more or less) for positive and negative excursions. There is no need to double the voltage, there is plenty of voltage and current available to light an LED. 

Howard

On 7/3/2018 11:25 PM, R. E. Klaus via Groups.Io wrote:
Doesn't the 2 diodes and the cap form a rudimentary voltage doubler similar to those used in old AC/DC radios?


Lee
 

Oh-Oh.  I figured out why my led was so bright.  The circuit was eating up my output.   The diagram my  PSK31 ham friend sent me is wrong.  It showed the bottom of the circuit grounded.  Nope, they needed to be connected together but not grounded.   I found a similar circuit which uses a capacitor instead of the resistor.  I now use a 2 volt green diffused LED which is easy to see but not as bright as the original but it does not load the output as before.

Here is a working circuit and whoever posted it on http://ubitx.net/ could they put up the corrected circuit.
--
Lee - N9LO  "I Void Warranties"

 

Mike Woods
 

Lee

I put it up on ubitx.net , but I have now corrected the diagram for you!  Glad you are now getting more power up the spout!

Mike ZL1AXG ubitx.net

On 10/07/18 8:17 AM, Lee wrote:
Oh-Oh.  I figured out why my led was so bright.  The circuit was eating up my output.   The diagram my  PSK31 ham friend sent me is wrong.  It showed the bottom of the circuit grounded.  Nope, they needed to be connected together but not grounded.   I found a similar circuit which uses a capacitor instead of the resistor.  I now use a 2 volt green diffused LED which is easy to see but not as bright as the original but it does not load the output as before.

Here is a working circuit and whoever posted it on http://ubitx.net/ could they put up the corrected circuit.
--
Lee - N9LO  "I Void Warranties"

 


--
Mike Woods
mhwoods@...