Field strength meter -- diode

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.

Reply to
mkr5000
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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

Reply to
Rich S

this looks like a good starting design with a wide signal level range..

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#2 from ...
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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

Reply to
Rich S

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

= RS

Reply to
Rich S

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.

Reply to
John Larkin

_Anything_ is better than an LM3900!

Cheers

Phil Hobbs

Reply to
Phil Hobbs

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

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** Such movement have around 3000 ohm R.
** 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

Reply to
Phil Allison

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:

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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.

Reply to
Jan Frank

Jan Frank wrote: ===============

** See specs INCLUDING the 9.999 mV range.

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..... Phil

Reply to
Phil Allison

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

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

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.

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.

Reply to
whit3rd

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

** NO it is NOT !!!
** Read my post - f****it.

** One div is the resolution - at best.

** The meter has has no such damn thing, you f****ng LIAR !!!,
** You on drugs ? LSD maybe ?? Cocaine ?
** FFS what a DESPERATE LIAR you are !!!!

FOAD you Dem pig.

Reply to
Phil Allison

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).

Reply to
whit3rd

Thirdwirt CONGENITAL LIAR : whit3rd vomityed:

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

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

BRAIN FUCKED Google monkeys like YOU cannot READ at all.

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

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

Reply to
Phil Allison

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.

Reply to
Dave Platt

On a sunny day (Fri, 31 Dec 2021 19:09:23 -0800) it happened snipped-for-privacy@highlandsniptechnology.com wrote in snipped-for-privacy@4ax.com:

For a yes / no detector this model works for me:

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For more info on the source, if between 30 MHz and about 2 GHz:
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of free spectrum analyzer software for it around.

This uses an OLED:

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Not sure I published the code, the bridge idea is not mine:
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I have a more SWR stuff.

Reply to
Jan Panteltje

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

Reply to
Phil Hobbs

There is no change when the range switch is partially rotated, so I don't think it is the problem. The reading simply wanders, and it gets worse as you go downrange. Obviously thermal drift.

I was thinking of replacing the input transistors with an LMC660 or modern equivalent and may do so if I ever need to monitor weak currents over a period of time.

But a better option would be to get a used 616 which offers autoranging and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on eBay - around $295 or so. But for now, the RM109 is more than adequate. It certainly beats the banggood galvanometer.

Reply to
Jan Frank

I ordered some parts and have yet to breadboard anything yet for a FSM. Got the schottkys and a couple germanium diode varieties, plus an FET.

What exactly is the value in this where he 2 diodes in series? Of course it's on youtube so....

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Reply to
mkr5000

Both JL and I have 610Cs that are far better than that. Yours must broken or badly contaminated. Mine easily measures down to the tens of femtoamps.

You can do a good job with that. I've been meaning to build a nice

100-pF charge-dispensing loop electrometer, but so far the 610C or even the old tube-based 405 have been better than good enough.

I haven't got a lot of use for a digital electrometer. Down in the picoamps and lower, seeing trends is much more important than high precision, not least because leakages are very unlikely to be stable to

3 sig figures.

(Plus I paid $5 plus shipping for my 405, $36 for a 602C, and $125 for the 610C on my bench.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Reply to
mkr5000

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