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Improving my best diode detector

Started by amdx April 19, 2017
Hi Guys,
  I have three Diode Detectors built as the Figure 4 schematic in this 
article, using different number diodes.

> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf
I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of some old pcbs. The best is the unknown germainums, which are probably 1N34A diodes. I have some on order to test. Here is a graph here showing the input at 1MHz and the DC output curves.
> https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0
It is actually better than I expected, but, The question; Is there any change I could make to improve it? Mikek --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
On Wednesday, 19 April 2017 16:13:38 UTC+1, amdx  wrote:
> Hi Guys, > I have three Diode Detectors built as the Figure 4 schematic in this > article, using different number diodes. > > > https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf > > I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of > some old pcbs. > The best is the unknown germainums, which are probably 1N34A diodes. I > have some on order to test. > > Here is a graph here showing the input at 1MHz and the DC output curves. > > https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0 > > It is actually better than I expected, but, > The question; Is there any change I could make to improve it? > > Mikek
Yes, you could label the axes. NT
On 4/19/2017 11:13 AM, amdx wrote:
> Hi Guys, > I have three Diode Detectors built as the Figure 4 schematic in this > article, using different number diodes. > >> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf >> > > I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of > some old pcbs. > The best is the unknown germainums, which are probably 1N34A diodes. I > have some on order to test. > > Here is a graph here showing the input at 1MHz and the DC output curves. >> https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0 >> > > It is actually better than I expected, but, > The question; Is there any change I could make to improve it?
I believe you care much less about the low end of the scale than the high end. So I would replace the two 4.7 kohm resistors with a 10 kohm pot and tweak it up a bit to improve the middle section of the curve. You can use a small pot with a slightly smaller than 18.13 kohm resistor to set the full scale point, then adjust the 10 kohm resisotr to get an accurate value at midscale. What is the purpose of the 68 ohm resistor? As the circuit is shown it does nothing but draw more current from the voltage source. I expect your driver will have some output resistance which will make the pair act as a voltage divider which isn't especially useful. The non-linearity of the diodes comes from the low voltage end of their characteristic. If you run with a lower input voltage it just accentuates the non-linearity. -- Rick C
On 4/19/2017 12:51 PM, rickman wrote:
> On 4/19/2017 11:13 AM, amdx wrote: >> Hi Guys, >> I have three Diode Detectors built as the Figure 4 schematic in this >> article, using different number diodes. >> >>> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf >>> >>> >> >> I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of >> some old pcbs. >> The best is the unknown germainums, which are probably 1N34A diodes. I >> have some on order to test. >> >> Here is a graph here showing the input at 1MHz and the DC output curves. >>> https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0 >>> >>> >> >> It is actually better than I expected, but, >> The question; Is there any change I could make to improve it? > > I believe you care much less about the low end of the scale than the > high end. So I would replace the two 4.7 kohm resistors with a 10 kohm > pot and tweak it up a bit to improve the middle section of the curve. > You can use a small pot with a slightly smaller than 18.13 kohm resistor > to set the full scale point, then adjust the 10 kohm resistor to get an > accurate value at midscale.
Your right I expect to run the large majority of tests in the upper 3/5ths of the meter range. I am not there yet I expect the graph to run up to 5Vrms, but I don't have a generator that will go that high. I assume it will not deviate from the linear line at the high end. Any agreement there? OK, I'll try the 10k pot. and run some more graphs.
> > What is the purpose of the 68 ohm resistor?
My guess would be to match the source, The author was working at 900MHz and 1.8GHz. I also note it is a return path for the first diode, some circuits replace the Resistor with an inductor for a dc return path but blocking the AC. I would like to run it from a higher impedance source, say 500 or even 1000 ohms, but I don't know how it would affect the output.
> What is the purpose of the 68 ohm resistor? >As the circuit is shown it > does nothing but draw more current from the voltage source. I expect > your driver will have some output resistance which will make the pair > act as a voltage divider which isn't especially useful. The > non-linearity of the diodes comes from the low voltage end of their > characteristic. If you run with a lower input voltage it just > accentuates the non-linearity. >
If I changed it to a 500 ohm resistor, I would have less current flow through the first diode and as you say accentuate the non-linearity. Mikek --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
On 4/19/2017 1:46 PM, amdx wrote:
> On 4/19/2017 12:51 PM, rickman wrote: >> On 4/19/2017 11:13 AM, amdx wrote: >>> Hi Guys, >>> I have three Diode Detectors built as the Figure 4 schematic in this >>> article, using different number diodes. >>> >>>> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf >>>> >>>> >>> >>> I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of >>> some old pcbs. >>> The best is the unknown germainums, which are probably 1N34A diodes. I >>> have some on order to test. >>> >>> Here is a graph here showing the input at 1MHz and the DC output curves. >>>> https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0 >>>> >>>> >>> >>> It is actually better than I expected, but, >>> The question; Is there any change I could make to improve it? >> >> I believe you care much less about the low end of the scale than the >> high end. So I would replace the two 4.7 kohm resistors with a 10 >> kohm pot and tweak it up a bit to improve the middle section of the >> curve. You can use a small pot with a slightly smaller than 18.13 kohm >> resistor to set the full scale point, then adjust the 10 kohm resistor >> to get an accurate value at midscale. > > Your right I expect to run the large majority of tests in the upper > 3/5ths of the meter range. I am not there yet I expect the graph to run > up to 5Vrms, but I don't have a generator that will go that high. > I assume it will not deviate from the linear line at the high end. > Any agreement there? > OK, I'll try the 10k pot. and run some more graphs. > >> >> What is the purpose of the 68 ohm resistor? > My guess would be to match the source, The author was working at > 900MHz and 1.8GHz. > I also note it is a return path for the first diode, some circuits > replace the Resistor with an inductor for a dc return path but blocking > the AC. > I would like to run it from a higher impedance source, say 500 or > even 1000 ohms, but I don't know how it would affect the output. > > >> What is the purpose of the 68 ohm resistor? >As the circuit is shown it >> does nothing but draw more current from the voltage source. I expect >> your driver will have some output resistance which will make the pair >> act as a voltage divider which isn't especially useful. The >> non-linearity of the diodes comes from the low voltage end of their >> characteristic. If you run with a lower input voltage it just >> accentuates the non-linearity. >> > If I changed it to a 500 ohm resistor, I would have less current flow > through the first diode and as you say accentuate the non-linearity. > Mikek
I changed the termination from 68 to 500 ohms. I made a few iterations until R2 is 3.915k and R1 is 5.85k and the line is really good. One thing I didn't do, I need to change the source to 500 ohms, this will match the amp I want to drive this with. Here's the graph.
> https://www.dropbox.com/s/3oyjn2teglg47b7/Diode%20detector%201N34A%20500ohm%20adjusted%20R1%20and%20R2.jpg?dl=0
Thanks for the suggestions, Mikek --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
On 4/19/2017 6:34 PM, amdx wrote:
> On 4/19/2017 1:46 PM, amdx wrote: >> On 4/19/2017 12:51 PM, rickman wrote: >>> On 4/19/2017 11:13 AM, amdx wrote: >>>> Hi Guys, >>>> I have three Diode Detectors built as the Figure 4 schematic in this >>>> article, using different number diodes. >>>> >>>>> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf >>>>> >>>>> >>>> >>>> I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of >>>> some old pcbs. >>>> The best is the unknown germainums, which are probably 1N34A diodes. I >>>> have some on order to test. >>>> >>>> Here is a graph here showing the input at 1MHz and the DC output >>>> curves. >>>>> https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0 >>>>> >>>>> >>>> >>>> It is actually better than I expected, but, >>>> The question; Is there any change I could make to improve it? >>> >>> I believe you care much less about the low end of the scale than the >>> high end. So I would replace the two 4.7 kohm resistors with a 10 >>> kohm pot and tweak it up a bit to improve the middle section of the >>> curve. You can use a small pot with a slightly smaller than 18.13 >>> kohm resistor to set the full scale point, then adjust the 10 kohm >>> resistor to get an accurate value at midscale. >> >> Your right I expect to run the large majority of tests in the upper >> 3/5ths of the meter range. I am not there yet I expect the graph to >> run up to 5Vrms, but I don't have a generator that will go that high. >> I assume it will not deviate from the linear line at the high end. >> Any agreement there? >> OK, I'll try the 10k pot. and run some more graphs. >> >>> >>> What is the purpose of the 68 ohm resistor? >> My guess would be to match the source, The author was working at >> 900MHz and 1.8GHz. >> I also note it is a return path for the first diode, some circuits >> replace the Resistor with an inductor for a dc return path but >> blocking the AC.
I have no idea why you need a special "return" path for the diode. The diode passes current one way, that is the point. There is no current the other way. The driving circuit won't care if no current flows the other way. The return path is through the meter and the other diode back to the other side of the voltage source. BTW, you talk about R numbers in your write ups, but the diagram has no R numbers to match up.
>> I would like to run it from a higher impedance source, say 500 or >> even 1000 ohms, but I don't know how it would affect the output.
Did you ever figure out what the impedance is of your amp?
>>> What is the purpose of the 68 ohm resistor? >As the circuit is shown it >>> does nothing but draw more current from the voltage source. I expect >>> your driver will have some output resistance which will make the pair >>> act as a voltage divider which isn't especially useful. The >>> non-linearity of the diodes comes from the low voltage end of their >>> characteristic. If you run with a lower input voltage it just >>> accentuates the non-linearity. >>> >> If I changed it to a 500 ohm resistor, I would have less current flow >> through the first diode and as you say accentuate the non-linearity.
Don't think so. The current through the diode comes from the voltage source, not the parallel resistor. If anything, the current will be higher without the 68 ohm resistor. Check out "Thevenin equivalent". The 68 ohm resistor creates a voltage divider with the source impedance and lowers the drive voltage more than it lowers the source impedance and so lowers the current through the rest of the circuit.
> I changed the termination from 68 to 500 ohms. > I made a few iterations until R2 is 3.915k and R1 is 5.85k > and the line is really good. > One thing I didn't do, I need to change the source to 500 ohms, > this will match the amp I want to drive this with. > Here's the graph. >> https://www.dropbox.com/s/3oyjn2teglg47b7/Diode%20detector%201N34A%20500ohm%20adjusted%20R1%20and%20R2.jpg?dl=0
That looks pretty durn good. But you need to see how it works with your amp driving it. -- Rick C
On 4/19/2017 11:57 PM, rickman wrote:
> On 4/19/2017 6:34 PM, amdx wrote: >> On 4/19/2017 1:46 PM, amdx wrote: >>> On 4/19/2017 12:51 PM, rickman wrote: >>>> On 4/19/2017 11:13 AM, amdx wrote: >>>>> Hi Guys, >>>>> I have three Diode Detectors built as the Figure 4 schematic in this >>>>> article, using different number diodes. >>>>> >>>>>> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf >>>>>> >>>>>> >>>>>> >>>>> >>>>> I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of >>>>> some old pcbs. >>>>> The best is the unknown germainums, which are probably 1N34A >>>>> diodes. I >>>>> have some on order to test. >>>>> >>>>> Here is a graph here showing the input at 1MHz and the DC output >>>>> curves. >>>>>> https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0 >>>>>> >>>>>> >>>>>> >>>>> >>>>> It is actually better than I expected, but, >>>>> The question; Is there any change I could make to improve it? >>>> >>>> I believe you care much less about the low end of the scale than the >>>> high end. So I would replace the two 4.7 kohm resistors with a 10 >>>> kohm pot and tweak it up a bit to improve the middle section of the >>>> curve. You can use a small pot with a slightly smaller than 18.13 >>>> kohm resistor to set the full scale point, then adjust the 10 kohm >>>> resistor to get an accurate value at midscale. >>> >>> Your right I expect to run the large majority of tests in the upper >>> 3/5ths of the meter range. I am not there yet I expect the graph to >>> run up to 5Vrms, but I don't have a generator that will go that high. >>> I assume it will not deviate from the linear line at the high end. >>> Any agreement there? >>> OK, I'll try the 10k pot. and run some more graphs. >>> >>>> >>>> What is the purpose of the 68 ohm resistor? >>> My guess would be to match the source, The author was working at >>> 900MHz and 1.8GHz. >>> I also note it is a return path for the first diode, some circuits >>> replace the Resistor with an inductor for a dc return path but >>> blocking the AC. > > I have no idea why you need a special "return" path for the diode. The > diode passes current one way, that is the point. There is no current > the other way. The driving circuit won't care if no current flows the > other way. The return path is through the meter and the other diode > back to the other side of the voltage source. >
The 68 was a simple termination resistor, I have dropped it, I also found that driving it from a 500 ohm source didn't have much effect on linearity. So that will worh with my existing amp impedance. It's all coming together now.
> BTW, you talk about R numbers in your write ups, but the diagram has no > R numbers to match up. >
The first resistor after the diode is R2 and the second is R1. Refer to this paper,
> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf
> >>> I would like to run it from a higher impedance source, say 500 or >>> even 1000 ohms, but I don't know how it would affect the output. > > Did you ever figure out what the impedance is of your amp?
Yes, it equals the collector resistor. Loading it with an equal resistance drops the output by half.
> > >>>> What is the purpose of the 68 ohm resistor? >As the circuit is shown it >>>> does nothing but draw more current from the voltage source. I expect >>>> your driver will have some output resistance which will make the pair >>>> act as a voltage divider which isn't especially useful. The >>>> non-linearity of the diodes comes from the low voltage end of their >>>> characteristic. If you run with a lower input voltage it just >>>> accentuates the non-linearity. >>>> >>> If I changed it to a 500 ohm resistor, I would have less current flow >>> through the first diode and as you say accentuate the non-linearity. > > Don't think so. The current through the diode comes from the voltage > source, not the parallel resistor. If anything, the current will be > higher without the 68 ohm resistor. Check out "Thevenin equivalent". > The 68 ohm resistor creates a voltage divider with the source impedance > and lowers the drive voltage more than it lowers the source impedance > and so lowers the current through the rest of the circuit. > >
Yep, dropped the termination, raised the driving impedance.
>> I changed the termination from 68 to 500 ohms. >> I made a few iterations until R2 is 3.915k and R1 is 5.85k >> and the line is really good. >> One thing I didn't do, I need to change the source to 500 ohms, >> this will match the amp I want to drive this with. >> Here's the graph. >>> https://www.dropbox.com/s/3oyjn2teglg47b7/Diode%20detector%201N34A%20500ohm%20adjusted%20R1%20and%20R2.jpg?dl=0 >>> > > That looks pretty durn good. But you need to see how it works with your > amp driving it. >
Yes, I very happy with how good it looks. Baby steps for me, so far I've only drove it with 450 ohm resistor in series with my 50 ohm generator. Thanks, Mikek --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
On 19/04/2017 16:13, amdx wrote:
> Hi Guys, > I have three Diode Detectors built as the Figure 4 schematic in this > article, using different number diodes. > >> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf >> > > I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of > some old pcbs. > The best is the unknown germainums, which are probably 1N34A diodes. I > have some on order to test. > > Here is a graph here showing the input at 1MHz and the DC output curves. >> https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0 >> > > It is actually better than I expected, but, > The question; Is there any change I could make to improve it?
Possibly. The thing to do to make life easier is subtract off the least squares best straight line and show the residuals x10 on the same scale. You perhaps want to concentrate on the fit to 0.7v-3v being most linear. Bat62 looks pretty good to me if you allow it to cross the y axis with a DC offset and ignore the region <0.5v entirely. -- Regards, Martin Brown
On 4/20/2017 7:37 AM, Martin Brown wrote:
> On 19/04/2017 16:13, amdx wrote: >> Hi Guys, >> I have three Diode Detectors built as the Figure 4 schematic in this >> article, using different number diodes. >> >>> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf >>> >>> >> >> I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of >> some old pcbs. >> The best is the unknown germainums, which are probably 1N34A diodes. I >> have some on order to test. >> >> Here is a graph here showing the input at 1MHz and the DC output curves. >>> https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0 >>> >>> >> >> It is actually better than I expected, but, >> The question; Is there any change I could make to improve it? > > Possibly. The thing to do to make life easier is subtract off the least > squares best straight line and show the residuals x10 on the same scale. > > You perhaps want to concentrate on the fit to 0.7v-3v being most linear. > > Bat62 looks pretty good to me if you allow it to cross the y axis with a > DC offset and ignore the region <0.5v entirely. >
The Range to optimize is 3Vrms to 5Vrms. I couldn't run my graph out to 5Vrms, I didn't have the capability, but I'm getting there. My RF millivolt meter only goes to 3volts, I have 100 to 1 adapter, but it seem to cause a 10% error. When using the Q meter the drive can be adjusted to keep the meter in that 3V to 5V range. I also think that will be the most linear range. Thanks, Mikek --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
On 20/04/2017 15:26, amdx wrote:
> On 4/20/2017 7:37 AM, Martin Brown wrote: >> On 19/04/2017 16:13, amdx wrote: >>> Hi Guys, >>> I have three Diode Detectors built as the Figure 4 schematic in this >>> article, using different number diodes. >>> >>>> https://www.rf-microwave.com/uploads/diodes/a_temperature_compensated_linear_diode_detector.pdf >>> >>> I used Bat62, 1n5711 and some unknown germanium diodes I pulled of of >>> some old pcbs. >>> The best is the unknown germainums, which are probably 1N34A diodes. I >>> have some on order to test. >>> >>> Here is a graph here showing the input at 1MHz and the DC output curves. >>>> https://www.dropbox.com/s/63hsukb7jyryeb1/Diode%20Deetector%201N34a%2C%20Bat62%2C1N5711.jpg?dl=0 >>> >>> It is actually better than I expected, but, >>> The question; Is there any change I could make to improve it? >> >> Possibly. The thing to do to make life easier is subtract off the >> least squares best straight line and show the residuals x10 on the >> same scale. >> >> You perhaps want to concentrate on the fit to 0.7v-3v being most linear. >> >> Bat62 looks pretty good to me if you allow it to cross the y axis with >> a DC offset and ignore the region <0.5v entirely. >> > > The Range to optimize is 3Vrms to 5Vrms. I couldn't run my graph out > to 5Vrms, I didn't have the capability, but I'm getting there. > My RF millivolt meter only goes to 3volts, I have 100 to 1 adapter, but > it seem to cause a 10% error. > When using the Q meter the drive can be adjusted to keep the meter in > that 3V to 5V range. I also think that will be the most linear range.
Why are you so concerned about linearity of your diode detector if you are merely using the detector to look for a resonance peak? All you require of its amplitude detection is that it is monotonically increasing with input voltage and not too frequency dependent. I think you really should be checking how it behaves at constant input amplitude over the range of frequencies that you expect to use... -- Regards, Martin Brown