Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.

Now that I'm old and stupid can someone tell me what that diode is doing please?

Thanks.

On Friday, December 31, 2021 at 7:20:03 PM UTC, mkr5000 wrote:
> Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.
>
> Now that I'm old and stupid can someone tell me what that diode is doing please?
>
> Thanks.

No worries, "old and stupid" is everyone's fate (if we're lucky).

I assume this is the circuit?:
https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html

the circuit needs a closed DC path in order for current to flow.
A RF coil would do that, but has very low impedance at low
signal frequencies - and so not much output to drive the meter. Using
a diode in its place allows the circuit to work down to a very
low-frequency cutoff (set by that 50n capacitor and the other
components in the circuit).

how practical this circuit really is, I'm not sure...
cheers, RS

On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:
> On Friday, December 31, 2021 at 7:20:03 PM UTC, mkr5000 wrote:
> > Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.
> >
> > Now that I'm old and stupid can someone tell me what that diode is doing please?
> >
> > Thanks.
> No worries, "old and stupid" is everyone's fate (if we're lucky).
>
> I assume this is the circuit?:
> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html
>
> the circuit needs a closed DC path in order for current to flow.
> A RF coil would do that, but has very low impedance at low
> signal frequencies - and so not much output to drive the meter. Using
> a diode in its place allows the circuit to work down to a very
> low-frequency cutoff (set by that 50n capacitor and the other
> components in the circuit).
>
> how practical this circuit really is, I'm not sure...
> cheers, RS

Gotcha. I spaced right through it needing a path. Would like to improve on it
to possibly be able to drive an on/off circuit with a 5v pull up/down or something.
Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
to the microvolt output of something like this? -- thanks

> Gotcha. I spaced right through it needing a path. Would like to improve on it
> to possibly be able to drive an on/off circuit with a 5v pull up/down or something.
> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
> to the microvolt output of something like this? -- thanks

If you just want to see "something is there"
and accuracy is not important, then the simple
circuits, using transistors are fine. But
if you want the reading to mean something
real (electric field strength in V/m, etc.), then
to get better linearity and range, I'd use an opamp.
Any low-power op-amp would be OK, as
long as it works at your battery's voltage.

(If the sensed field strengths are high, then
the amp stage may not be needed - the
output from the diode can drive a sensitive
meter directly.)

I'd pull out my ARRL Handbook at this point.
to give you more details.
(My copy is in my office, far away...)
Maybe we can find something online...

=RS

On Friday, December 31, 2021 at 9:23:42 PM UTC, Rich S wrote:
> > Gotcha. I spaced right through it needing a path. Would like to improve on it
> > to possibly be able to drive an on/off circuit with a 5v pull up/down or something.
> > Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
> > to the microvolt output of something like this? -- thanks
> If you just want to see "something is there"
> and accuracy is not important, then the simple
> circuits, using transistors are fine. But
> if you want the reading to mean something
> real (electric field strength in V/m, etc.), then
> to get better linearity and range, I'd use an opamp.
> Any low-power op-amp would be OK, as
> long as it works at your battery's voltage.
>
> (If the sensed field strengths are high, then
> the amp stage may not be needed - the
> output from the diode can drive a sensitive
> meter directly.)
>
> I'd pull out my ARRL Handbook at this point.
> to give you more details.
> (My copy is in my office, far away...)
> Maybe we can find something online...
>
> =RS

this looks like a good starting design
with a wide signal level range..
http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/Images/Corrected-202107-QST-Schematic.png
(Schematic #2 from ...
http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/ARRL_QST_FDM_Schematic_Corrections.html
) Though we could do much better, a modern choice,
for the opamp, instead of an LM3900. Like,
MCP6041-I/P
MCP6043-I/P
MCP606-I/P
MCP6141-I/P
MCP6143-I/P
NJU7001D
NJU7021D
NJU7031D
NJU7051D
NJU7061D
OPA705PA
RE46C311E8F
TLV2760IP
TLV2761IP

= RS

> this looks like a good starting design
> with a wide signal level range..
> http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/Images/Corrected-202107-QST-Schematic.png
> (Schematic #2 from ...
> http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/ARRL_QST_FDM_Schematic_Corrections.html
> )
> Though we could do much better, a modern choice,
> for the opamp, instead of an LM3900. Like,

And Let's narrow down that list to just those with Rail to Rail Inputs
MCP6041
MCP6043
MCP6141
MCP6143
OPA705PA
RE46C311

= RS

On Fri, 31 Dec 2021 11:19:59 -0800 (PST), mkr5000 <mikerbgr@gmail.com>
wrote:

>Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.
>
>Now that I'm old and stupid can someone tell me what that diode is doing please?
>
>Thanks.

It's basically a 2-diode half-wave voltage doubler.

A low barrier schottky diode might work better than the germanium
antique, especially at high frequencies.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon

Rich S wrote:
>
>> this looks like a good starting design
>> with a wide signal level range..
>> http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/Images/Corrected-202107-QST-Schematic.png
>> (Schematic #2 from ...
>> http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/ARRL_QST_FDM_Schematic_Corrections.html
>> )
>> Though we could do much better, a modern choice,
>> for the opamp, instead of an LM3900. Like,
>
> And Let's narrow down that list to just those with Rail to Rail Inputs
> MCP6041
> MCP6043
> MCP6141
> MCP6143
> OPA705PA
> RE46C311
>
> = RS
>

_Anything_ is better than an LM3900!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:

> > https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html
> >
> > the circuit needs a closed DC path in order for current to flow.

> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
> to the microvolt output of something like this? -- thanks

<https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html>

A moving-needle meter for 30 uA with 100 ohms internal resistance can cover the
3mV range, with 30 uV easily resolved. Add a battery for collector bias, and
use a low-noise transistor B-E instead of one diode, and you're good for lower signals.

So low, in fact, that some frequency tuning is a wise addition.

On Fri, 31 Dec 2021 16:19:49 -0800, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

>On Fri, 31 Dec 2021 11:19:59 -0800 (PST), mkr5000 <mikerbgr@gmail.com>
>wrote:
>>Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.
>>Now that I'm old and stupid can someone tell me what that diode is doing please?

>It's basically a 2-diode half-wave voltage doubler.

Yep. More on how it works including an LTSpice model output (without
the actual model):
<http://k6jca.blogspot.com/2020/11/understanding-basic-rf-field-strength.html>

>A low barrier schottky diode might work better than the germanium
>antique, especially at high frequencies.

Yep.
"RF and microwave power detection with Schottky diodes"
<https://www.infineon.com/dgdl/Infineon-AN_1807_PL32_1808_132434_RF%20and%20microwave%20power%20detection%20-AN-v01_00-EN.pdf?fileId=5546d46265f064ff0166440727be1055>
The voltage doubler arrangement is Fig 15 (Pg 10).

--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

Thirdwit strike again: whit3rd wrote:

============================

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html

>
> A moving-needle meter for 30 uA with 100 ohms internal resistance

** Such movement have around 3000 ohm R.

> can cover the 3mV range, with 30 uV easily resolved.

** Horse poo.

The meter shown has a 30-0-30 uA range.
Resolution is 1uA.
Equates to 3mV DC
Any DMM will resolve 0.1 mV.

FOAD

..... Phil

On Fri, 31 Dec 2021 17:59:02 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>On Fri, 31 Dec 2021 16:19:49 -0800, John Larkin
><jlarkin@highland_atwork_technology.com> wrote:
>
>>On Fri, 31 Dec 2021 11:19:59 -0800 (PST), mkr5000 <mikerbgr@gmail.com>
>>wrote:
>>>Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.
>>>Now that I'm old and stupid can someone tell me what that diode is doing please?
>
>>It's basically a 2-diode half-wave voltage doubler.
>
>Yep. More on how it works including an LTSpice model output (without
>the actual model):
><http://k6jca.blogspot.com/2020/11/understanding-basic-rf-field-strength.html>
>
>>A low barrier schottky diode might work better than the germanium
>>antique, especially at high frequencies.
>
>Yep.
>"RF and microwave power detection with Schottky diodes"
><https://www.infineon.com/dgdl/Infineon-AN_1807_PL32_1808_132434_RF%20and%20microwave%20power%20detection%20-AN-v01_00-EN.pdf?fileId=5546d46265f064ff0166440727be1055>
>The voltage doubler arrangement is Fig 15 (Pg 10).

BAT15 is a nice part. Almost the same as an SMS7621.

The circuit in fig 15 works better without RL. Go into a cmos opamp or
comparator. The BAT15 has an Is of over 100 nA, so the diodes
discharge the output cap when the signal goes away.

That freaks some people out, which is always a good thing to do.

https://www.dropbox.com/s/oz821ocx7d62lng/K420_Sig_Det.jpg?raw=1

--

I yam what I yam - Popeye

whit3rd <whit3rd@gmail.com> wrote:

> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Senso
> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.ht
> ml>

The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift.

With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.

My favorite electrometer is the Kiethley 610C, which only goes down to 1e-
11 A full scale, and drifts like hell.

The RM109 is $31.46 on Amazon Canada:
https://www.amazon.ca/Alician-RICHMETERS-Multimeter-Backlight-
Voltmeter/dp/B086VH3NNP/

It is probably cheaper on Amazon US.

I can't find it on Banggood, but it is on Aliexpress for about the same
price to Canada. However, beware of counterfeits on Asian sites. I have
been burned badly.

There is another model of the Richmeter that measures temperature. It is on
a shelf I can't reach right now so I can't give you the model number.

Here are the specs for the RM 109 True RMS Multimeter.

DC Current: 60mA/600mA/10A
DC Voltage: 999.9mV/9.999V/99.99V/750V
AC Current: 60mA/600mA/10A
AC Voltage: 999.9mV/9.999V/99.99V/999.9V
Backlight Time: 120 Seconds
Capacitance: 9.99nF/99.99nF/999.9nF/9.99uF/99.99uF/999.9uF/9.999MF
Continuity: Yes
Dimensions: 65x130x32 mm
Diode Test: Yes
Display Type: 4 1/2 digits
Duty Cycle: 1%-99%
Frequency: 99.99Hz/999.9Hz/9.999KHz/99.99KHz/999.9KHz/9.999MHz
Operating Mode: Auto/Manual Ranging
Operating Temperature: 0 - 40
Resistance: 99.99/999.9/9.999k/99.99k/999.9K/999.9M
Special Function: Voltage Function have Low Frequency test function
Square Wave Output: 50Hz/100Hz/200Hz/300Hz/400Hz/500Hz/600Hz/700Hz/800Hz/
900Hz/1000Hz/200

For some bizarre reason they omit the mV range, which you can see on the
Amazon site. It is third up from the OFF position. This is the range that
gives 1uV resolution.

Jan Frank wrote:
===============
>
> The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
> parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift.
>
> With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.
>
> My favorite electrometer is the Kiethley 610C, which only goes down to 1e-
> 11 A full scale, and drifts like hell.
>
> The RM109 is $31.46 on Amazon Canada:

** See specs INCLUDING the 9.999 mV range.

https://www.alibaba.com/product-detail/RICHMETERS-RM109-Palm-size-True-RMS_60768171490.html

...... Phil

On Friday, December 31, 2021 at 6:12:44 PM UTC-8, palli...@gmail.com wrote:
> whit3rd wrote:

>> https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html
>
> >
> > A moving-needle meter for 30 uA with 100 ohms internal resistance
> ** Such movement have around 3000 ohm R.

Review the link. Internal resistance is marked as 100 ohms.

> > can cover the 3mV range, with 30 uV easily resolved.
> ** Horse poo.
??
A needle that swings circa 100 mm, you can read to
a millimeter or less.

> The meter shown has a 30-0-30 uA range.
> Resolution is 1uA.

Not if you have normal eyesight. With a vernier scale, you can pick out
a thousandth of an inch. Mirror scales help, too (though neither is on the depicted model).
Anyone who ever used a slide rule knows to interpolate between marks.

> Equates to 3mV DC
> Any DMM will resolve 0.1 mV.

Zero won't be accurate for analog or DMM either, but twitches of the meter
might be more significant than a dancing last-digit of a digital display.

Thirdwit Congenital LAIR whit3rd wrote:
================================

> >
> > > A moving-needle meter for 30 uA with 100 ohms internal resistance
>
> > ** Such movement have around 3000 ohm R.
>
> Review the link. Internal resistance is marked as 100 ohms.

** NO it is NOT !!!

> > > can cover the 3mV range, with 30 uV easily resolved.
> > ** Horse poo.
> ??

** Read my post - fuckwit.

> A needle that swings circa 100 mm, you can read to
> a millimeter or less.

** One div is the resolution - at best.

> > The meter shown has a 30-0-30 uA range.
> > Resolution is 1uA.

> Not if you have normal eyesight. With a vernier scale,

** The meter has has no such damn thing, you fucking LIAR !!!,

> you can pick out a thousandth of an inch.

** You on drugs ? LSD maybe ?? Cocaine ?

> > Equates to 3mV DC
> > Any DMM will resolve 0.1 mV.
>
> Zero won't be accurate for analog or DMM either,

** FFS what a DESPERATE LIAR you are !!!!

FOAD you Dem pig.

On Friday, December 31, 2021 at 9:11:25 PM UTC-8, palli...@gmail.com wrote:
> whit3rd wrote:

> > > The meter shown has a 30-0-30 uA range.
> > > Resolution is 1uA.
>
> > Not if you have normal eyesight. With a vernier scale,
> ** The meter has has no such damn thing, you fucking LIAR !!!,
> > you can pick out a thousandth of an inch.
> ** You on drugs ? LSD maybe ?? Cocaine ?
> > > Equates to 3mV DC
> > > Any DMM will resolve 0.1 mV.
> >
> > Zero won't be accurate for analog or DMM either,

> ** FFS what a DESPERATE LIAR you are !!!!

Read for content, not for vitriol; the reading on a microvolt-resolution
instrument is only useful for thermocouple circuitry, OR for something
in a stirred constant-temperature bath. Accuracy at that level is impossible
where dissimilar metals and normal thermal gradients abound,
but precision is another story, as is timing (like, looking at a
cellphone sending a burst and causing a periodic brief twitch).

Thirdwirt CONGENITAL LIAR : whit3rd vomityed:

===============================
>
> > > > The meter shown has a 30-0-30 uA range.
> > > > Resolution is 1uA.
> >
> > > Not if you have normal eyesight. With a vernier scale,
> > ** The meter has has no such damn thing, you fucking LIAR !!!,
> > > you can pick out a thousandth of an inch.
> > ** You on drugs ? LSD maybe ?? Cocaine ?
> > > > Equates to 3mV DC
> > > > Any DMM will resolve 0.1 mV.
> > >
> > > Zero won't be accurate for analog or DMM either,
>
> > ** FFS what a DESPERATE LIAR you are !!!!
>
> Read for content,

** ROTFLMAO !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

BRAIN FUCKED Google monkeys like YOU cannot READ at all.

> the reading on a microvolt-resolution

** MASSIVE RED HERRING !!!!!!!

Your mom was a drug addict and you are brain dead.

In article <b623673b-5837-44c7-b53c-1515a6db9cfdn@googlegroups.com>,
Rich S <richsulinengineer@gmail.com> wrote:

>Though we could do much better, a modern choice,
>for the opamp, instead of an LM3900. Like,

Just remember that the LM3900 is a Norton amplifier, not a classic op
amp with symmetrical inputs. You may be able to drop a standard
"single supply" op amp into an LM3900 circuit without having to change
things around, but possibly not.

On a sunny day (Fri, 31 Dec 2021 19:09:23 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
<btgvsghggbcuhad95dj2u2jo1t1d218b8q@4ax.com>:

>The circuit in fig 15 works better without RL. Go into a cmos opamp or
>comparator. The BAT15 has an Is of over 100 nA, so the diodes
>discharge the output cap when the signal goes away.
>
>That freaks some people out, which is always a good thing to do.
>
>https://www.dropbox.com/s/oz821ocx7d62lng/K420_Sig_Det.jpg?raw=1

For a yes / no detector this model works for me:
https://www.ebay.com/itm/313759590627?hash=item490d8768e3:g:31oAAOSwTdlhl2fr

For more info on the source, if between 30 MHz and about 2 GHz:
https://www.ebay.com/itm/272411458376
plenty of free spectrum analyzer software for it around.

This uses an OLED:
http://panteltje.com/pub/SWR_bridge_IMG_5051.JPG
http://panteltje.com/pub/SWR_bridge_circuit_diagram_IMG_5053.JPG

Not sure I published the code, the bridge idea is not mine:
http://panteltje.com/pub/SWR_bridge_on_dummy_load_IMG_5046.JPG

I have a more SWR stuff.

On 01/01/2022 01:19, whit3rd wrote:
> On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
>> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:
>
>>> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html
>>>
>>> the circuit needs a closed DC path in order for current to flow.
>
>
>
>> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
>> to the microvolt output of something like this? -- thanks
>
> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html>
>
> A moving-needle meter for 30 uA with 100 ohms internal resistance can cover the
> 3mV range, with 30 uV easily resolved. Add a battery for collector bias, and
> use a low-noise transistor B-E instead of one diode, and you're good for lower signals.
>
> So low, in fact, that some frequency tuning is a wise addition.

Excuse my ignorance, but why in the "Description" does it say that it's
a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive
Range: -300-0-300μA"?

And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is
connected in series in the circuit, the higher end of the "G" terminal
is used." That would give it an FSD of 72mV, wouldn't it? Is there a
reason why it's 2.4kohm rather than another value?

--

Jeff

On Friday, December 31, 2021 at 11:56:07 PM UTC-8, Jeff Layman wrote:
> On 01/01/2022 01:19, whit3rd wrote:
> > On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
> >> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:
> >
> >>> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html
> >>>
> >>> the circuit needs a closed DC path in order for current to flow.
> >
> >
> >
> >> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
> >> to the microvolt output of something like this? -- thanks
> >
> > <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html>

> Excuse my ignorance, but why in the "Description" does it say that it's
> a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive
> Range: -300-0-300μA"?

Yeah, that's a mystery.

> And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is
> connected in series in the circuit, the higher end of the "G" terminal
> is used." That would give it an FSD of 72mV, wouldn't it? Is there a
> reason why it's 2.4kohm rather than another value?

It's usual in these things to provide some damping (a shunt resistor or R-C
snubber) across the bare galvanometer, and there's a particular value
that (with the coil inductance) is most effective. That's the only
resistor value I'd expect to see built-in. The merchant might not
know what it's for, but damping makes the needle return to zero
between measurements instead of oscillating for a few seconds.

On 01/01/2022 08:28, whit3rd wrote:
> On Friday, December 31, 2021 at 11:56:07 PM UTC-8, Jeff Layman wrote:
>> On 01/01/2022 01:19, whit3rd wrote:
>>> On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
>>>> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:
>>>
>>>>> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html
>>>>>
>>>>> the circuit needs a closed DC path in order for current to flow.
>>>
>>>
>>>
>>>> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
>>>> to the microvolt output of something like this? -- thanks
>>>
>>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html>
>
>> Excuse my ignorance, but why in the "Description" does it say that it's
>> a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive
>> Range: -300-0-300μA"?
>
> Yeah, that's a mystery.

Probably just a misprint or mistranslation.

>> And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is
>> connected in series in the circuit, the higher end of the "G" terminal
>> is used." That would give it an FSD of 72mV, wouldn't it? Is there a
>> reason why it's 2.4kohm rather than another value?
>
> It's usual in these things to provide some damping (a shunt resistor or R-C
> snubber) across the bare galvanometer, and there's a particular value
> that (with the coil inductance) is most effective. That's the only
> resistor value I'd expect to see built-in. The merchant might not
> know what it's for, but damping makes the needle return to zero
> between measurements instead of oscillating for a few seconds.

OK. Makes sense. Just don't try try to push it to -300-0-300μA! :-)

--

Jeff

On Saturday, January 1, 2022 at 4:06:56 AM UTC-5, Jeff Layman wrote:
> On 01/01/2022 08:28, whit3rd wrote:
> > On Friday, December 31, 2021 at 11:56:07 PM UTC-8, Jeff Layman wrote:
> >> On 01/01/2022 01:19, whit3rd wrote:
> >>> On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
> >>>> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:
> >>>
> >>>>> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html
> >>>>>
> >>>>> the circuit needs a closed DC path in order for current to flow.
> >>>
> >>>
> >>>
> >>>> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
> >>>> to the microvolt output of something like this? -- thanks
> >>>
> >>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html>
> >
> >> Excuse my ignorance, but why in the "Description" does it say that it's
> >> a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive
> >> Range: -300-0-300μA"?
> >
> > Yeah, that's a mystery.
> Probably just a misprint or mistranslation.
> >> And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is
> >> connected in series in the circuit, the higher end of the "G" terminal
> >> is used." That would give it an FSD of 72mV, wouldn't it? Is there a
> >> reason why it's 2.4kohm rather than another value?
> >
> > It's usual in these things to provide some damping (a shunt resistor or R-C
> > snubber) across the bare galvanometer, and there's a particular value
> > that (with the coil inductance) is most effective. That's the only
> > resistor value I'd expect to see built-in. The merchant might not
> > know what it's for, but damping makes the needle return to zero
> > between measurements instead of oscillating for a few seconds.
> OK. Makes sense. Just don't try try to push it to -300-0-300μA! :-)
>
> --
>
> Jeff
Thanks for the suggestion on the BA15T -- just ordered the one with 2 diodes enclosed. I have just a single 5v supply to utilize so hoping I can get a circuit going using an LM358 ? I have a ton of those. Unless another single supply op amp would be better. (I'm a play around with it till it works guy -- you guys are the legit designers). The goal is to get a digital on/off when an rf field is detected on one side of a comparator. Should be easy enough.

It's for an amateur radio situation. Hopefully just a piece of wire near the xcvr will be fine. (Rather than maybe having to rely on the antenna). We'll see..... things are pretty well shielded these days.

It's not the old Knight kit I had.

Now quit pickin' on each other you guys. !

Jan Frank wrote:
> whit3rd <whit3rd@gmail.com> wrote:
>
>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Senso
>> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.ht
>> ml>
>
> The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
> parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift.
>
> With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.
>
> My favorite electrometer is the Kiethley 610C, which only goes down to 1e-
> 11 A full scale, and drifts like hell.

Nah, there's the range multiplier knob that gets you another factor of
100 on the FS range, so you get a 10-fA FSR on that box.

Of course that one is too unstable to be useful, but the 100-fA FS range
is pretty good, at least on my unit. Yours may need cleaning or repair.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com