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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
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
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,
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.
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 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
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.
A low barrier schottky diode might work better than the germanium
antique, especially at high frequencies.
A moving-needle meter for 30 uA with 100 ohms internal resistance
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).
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:
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.
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,
Equates to 3mV DC
Any DMM will resolve 0.1 mV.
Zero won\'t be accurate for analog or DMM either,
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 !!!!
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,
Though we could do much better, a modern choice,
for the opamp, instead of an LM3900. Like,
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