Maker Pro
Maker Pro

Field Strength Meter (LTspice)

A

analog

Jan 1, 1970
0
Version 4
SHEET 1 880 680
WIRE -880 32 -864 32
WIRE -784 32 -768 32
WIRE -288 -176 -512 -176
WIRE 496 -176 496 -112
WIRE 496 -32 496 32
WIRE 496 320 304 320
WIRE 0 320 -416 320
WIRE -672 32 -672 112
WIRE -672 32 -624 32
WIRE -400 32 -416 32
WIRE -288 32 -288 -32
WIRE -288 -176 0 -176
WIRE 0 -176 304 -176
WIRE -288 -112 -288 -176
WIRE -352 96 -352 128
WIRE -512 -112 -512 -176
WIRE -528 32 -512 32
WIRE -512 32 -496 32
WIRE -512 32 -512 -32
WIRE -672 288 -672 320
WIRE -576 96 -576 112
WIRE 496 32 496 80
WIRE -592 112 -576 112
WIRE -576 128 -576 112
WIRE -672 112 -656 112
WIRE -432 32 -416 32
WIRE -416 32 -416 208
WIRE 496 240 496 320
WIRE 496 80 560 80
WIRE 0 288 0 320
WIRE -208 32 -192 32
WIRE -192 64 -192 32
WIRE -192 32 -144 32
WIRE 0 -16 0 -176
WIRE -192 144 -192 176
WIRE 0 208 0 176
WIRE 368 32 400 32
WIRE 400 64 400 32
WIRE 400 144 400 176
WIRE 304 -176 496 -176
WIRE -768 32 -752 32
WIRE 304 208 304 176
WIRE 304 -16 304 -176
WIRE 400 32 416 32
WIRE 480 32 496 32
WIRE -192 176 -176 176
WIRE -112 176 -96 176
WIRE -192 176 -192 192
WIRE 304 288 304 320
WIRE 304 320 0 320
WIRE 304 176 320 176
WIRE 384 176 400 176
WIRE 400 176 400 192
WIRE 304 176 304 128
WIRE 0 128 16 128
WIRE 0 128 0 80
WIRE 304 128 304 80
WIRE 496 80 496 160
WIRE -272 32 -288 32
WIRE -288 32 -304 32
WIRE -416 288 -416 320
WIRE -416 320 -672 320
WIRE -672 112 -672 208
WIRE -688 32 -672 32
WIRE 496 -176 624 -176
WIRE 624 -176 624 -112
WIRE 624 -48 624 80
WIRE 624 320 496 320
WIRE 624 80 624 160
WIRE 560 80 560 96
WIRE 560 80 624 80
WIRE 624 224 624 320
WIRE 288 128 304 128
WIRE -96 32 -96 64
WIRE -96 128 -96 176
WIRE -96 32 -64 32
WIRE -96 176 0 176
WIRE 0 176 0 128
WIRE -144 32 -96 32
WIRE 16 128 96 128
WIRE 208 32 208 128
WIRE 208 128 288 128
WIRE 96 32 112 32
WIRE 192 32 208 32
WIRE 96 128 96 32
WIRE 96 128 128 128
WIRE 192 128 208 128
FLAG -880 32 0
FLAG -768 32 1
FLAG -672 32 2
FLAG -576 128 0
FLAG -352 128 0
FLAG -192 192 0
FLAG 400 192 0
FLAG 560 96 0
FLAG -512 32 3
FLAG -416 32 4
FLAG -288 32 5
FLAG -144 32 6
FLAG 16 128 7
FLAG 288 128 8
FLAG 400 32 9
SYMBOL ind -528 -128 R0
WINDOW 0 40 32 Left 0
WINDOW 3 40 57 Left 0
WINDOW 39 40 80 Left 0
SYMATTR InstName L1
SYMATTR Value 1µ0
SYMATTR SpiceLine Rpar=3k
SYMBOL npn -528 96 M270
WINDOW 0 80 48 VBottom 0
WINDOW 3 80 48 VTop 0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL cap -752 48 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName C1
SYMATTR Value 1n
SYMBOL cap -496 48 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName C2
SYMATTR Value 10p
SYMBOL res -688 192 R0
SYMATTR InstName R1
SYMATTR Value 1k0
SYMBOL diode -656 128 R270
WINDOW 0 -32 32 VTop 0
WINDOW 3 -32 32 VBottom 0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL voltage -768 32 M270
WINDOW 123 -43 57 VBottom 0
WINDOW 39 -78 60 VBottom 0
WINDOW 0 32 56 VTop 0
WINDOW 3 -112 57 VBottom 0
SYMATTR Value2 AC 1
SYMATTR SpiceLine Rser=33
SYMATTR InstName V1
SYMATTR Value SINE(0 5m 40.5e6)
SYMBOL npn -304 96 M270
WINDOW 0 80 48 VBottom 0
WINDOW 3 80 48 VTop 0
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL cap -208 16 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C3
SYMATTR Value 1n
SYMBOL res -432 192 R0
SYMATTR InstName R2
SYMATTR Value 1k0
SYMBOL npn -64 -16 R0
SYMATTR InstName Q3
SYMATTR Value 2N3904
SYMBOL res -208 48 R0
WINDOW 3 36 64 Left 0
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL npn 368 -16 M0
SYMATTR InstName Q4
SYMATTR Value 2N3904
SYMBOL cap 480 16 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C4
SYMATTR Value 1n
SYMBOL res 288 192 R0
WINDOW 0 -5 40 Right 0
WINDOW 3 -5 75 Right 0
SYMATTR InstName R6
SYMATTR Value 1k0
SYMBOL res 384 48 R0
WINDOW 0 -4 40 Right 0
WINDOW 3 -4 64 Right 0
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL cap -112 160 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C5
SYMATTR Value 10n
SYMBOL res -16 192 R0
SYMATTR InstName R5
SYMATTR Value 1k0
SYMBOL cap 384 160 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C6
SYMATTR Value 10n
SYMBOL Misc\\battery 496 -128 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 132 Left 0
SYMATTR InstName V2
SYMATTR Value 2.8V
SYMATTR SpiceLine Rser=1
SYMBOL Misc\\battery 496 144 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 132 Left 0
SYMATTR InstName V3
SYMATTR Value 2.8V
SYMATTR SpiceLine Rser=1
SYMBOL ind -304 -128 R0
WINDOW 0 40 32 Left 0
WINDOW 3 40 57 Left 0
WINDOW 39 40 80 Left 0
SYMATTR InstName L2
SYMATTR Value 1µ0
SYMATTR SpiceLine Rpar=3k
SYMBOL cap 608 -112 R0
SYMATTR InstName C7
SYMATTR Value 10n
SYMBOL cap 608 160 R0
SYMATTR InstName C8
SYMATTR Value 10n
SYMBOL ind 96 48 R270
WINDOW 0 32 56 VTop 0
WINDOW 3 5 56 VBottom 0
WINDOW 39 71 56 VCenter 0
SYMATTR InstName Lmeter
SYMATTR Value 10µ
SYMATTR SpiceLine Rser=380
SYMBOL diode -112 128 M180
WINDOW 0 36 40 Left 0
WINDOW 3 19 2 Left 0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL diode 128 112 M90
WINDOW 0 0 24 VBottom 0
WINDOW 3 32 24 VTop 0
SYMATTR InstName D3
SYMATTR Value 1N4148
TEXT -944 -160 Left 0 !.tran 0 1m 0 10n
TEXT -944 -120 Left 0 !.ac dec 101 1e6 1e9
TEXT -944 -80 Left 0 ;.step param n list .5 1 2
TEXT 152 -48 Center 0 ;100ua
 
J

James Meyer

Jan 1, 1970
0
Version 4
SHEET 1 880 680
WIRE -880 32 -864 32
WIRE -784 32 -768 32
............
TEXT -944 -160 Left 0 !.tran 0 1m 0 10n
TEXT -944 -120 Left 0 !.ac dec 101 1e6 1e9
TEXT -944 -80 Left 0 ;.step param n list .5 1 2
TEXT 152 -48 Center 0 ;100ua

Excellent!

That's just the circuit I would have come up with if I were one tenth
tha analog circuit designer I wished I was.

One question... you included the ability to step a parameter, but I
didn't see where the parameter was used. It would be really nice to get a plot
of meter current verses input RF voltage amplitude. Was that what the parameter
was intended for?

Jim "Humble before Analog" Meyer

P.S. Paul, go ahead and lay out Analog's circuit as a PC board. It's a winner.
 
P

Paul Burridge

Jan 1, 1970
0
Version 4
SHEET 1 880 680
WIRE -880 32 -864 32
WIRE -784 32 -768 32
WIRE -288 -176 -512 -176

Erm, what's this about?
 
P

Paul Burridge

Jan 1, 1970
0
Excellent!

That's just the circuit I would have come up with if I were one tenth
tha analog circuit designer I wished I was.

One question... you included the ability to step a parameter, but I
didn't see where the parameter was used. It would be really nice to get a plot
of meter current verses input RF voltage amplitude. Was that what the parameter
was intended for?

Jim "Humble before Analog" Meyer

P.S. Paul, go ahead and lay out Analog's circuit as a PC board. It's a winner.

Sorry, I've only just found how to get LTS to recognise this but it's
fine now. There are a couple of questions I have but I'll run a few
sims first and see how it performs. I wonder how the hell he came up
with this design? It looks pretty unconventional to my inexperienced
eyes!
 
H

Helmut Sennewald

Jan 1, 1970
0
Hello "analog",
your circuit is accidentally less sensitive for lower input levels.
This makes it less useful if somebody wants an indicator for more than
one decade of signal level.

Input Volt. Meter current:
0mV -0.05uA
1mV 7.7uA
2mV 17.4uA
3mV 38.3uA
4mV 64.9uA
5mV 114.6uA

I have seen years ago this circuit.
http://www.reed-electronics.com/ednmag/contents/images/60701di.pdf
I am shure that this circuit will work at 40MHZ too, at least with a
HF-transistor. By the way, a higher resistor in the base makes it more
linear for lower levels. It will need an additional preamplifier too.

Overall it would make more sense to look for an integrated receiver IC
with a RSSI output. These ICs cover 60dB to 80dB dynamic range.
Google: rssi signal strength indicator IC
Hopefully somebody else can give an advice about a readily available
IC for 40MHz. There are many, but which of them is in reach for a
hobby project?

Best Regards,
Helmut
 
J

Jim Thompson

Jan 1, 1970
0
Hello "analog",
your circuit is accidentally less sensitive for lower input levels.
This makes it less useful if somebody wants an indicator for more than
one decade of signal level.

Input Volt. Meter current:
0mV -0.05uA
1mV 7.7uA
2mV 17.4uA
3mV 38.3uA
4mV 64.9uA
5mV 114.6uA

I have seen years ago this circuit.
http://www.reed-electronics.com/ednmag/contents/images/60701di.pdf
I am shure that this circuit will work at 40MHZ too, at least with a
HF-transistor. By the way, a higher resistor in the base makes it more
linear for lower levels. It will need an additional preamplifier too.

Overall it would make more sense to look for an integrated receiver IC
with a RSSI output. These ICs cover 60dB to 80dB dynamic range.
Google: rssi signal strength indicator IC
Hopefully somebody else can give an advice about a readily available
IC for 40MHz. There are many, but which of them is in reach for a
hobby project?

Best Regards,
Helmut

Clever use of an inverted device!

...Jim Thompson
 
J

James Meyer

Jan 1, 1970
0
Sorry, I've only just found how to get LTS to recognise this but it's
fine now. There are a couple of questions I have but I'll run a few
sims first and see how it performs. I wonder how the hell he came up
with this design? It looks pretty unconventional to my inexperienced
eyes!

It's as conventional as they come. Common base configurations were used
a lot in the early days of transistors when you couldn't just go out and buy a
better transistor. Hell, there were only three or four different transistors at
all in the beginning. You needed to push the transistors as hard as you could
to get them to work at high frequencies. I remember GE taking out a large
magazine ad for one of their improved transistors that would actually oscillate
all the way up to the top end of the AM band at 1.5 megacycles.

Jim
 
F

Fred Bloggs

Jan 1, 1970
0
Paul said:
Sorry, I've only just found how to get LTS to recognise this but it's
fine now. There are a couple of questions I have but I'll run a few
sims first and see how it performs. I wonder how the hell he came up
with this design? It looks pretty unconventional to my inexperienced
eyes!

Nah- it is a simple cascade of two common-base tuned gain stages driving
a single-ended to differential emitter coupled peak detector biased into
the linear region for greatest sensitivity and differential for zero DC
offset. It is non-inverting all the way so that layout will be
critical to prevent that huge gain from feeding back output to the
input. It is a good circuit for DIY and experimentation.
 
F

Fred Bloggs

Jan 1, 1970
0
Helmut said:
Hello "analog",
your circuit is accidentally less sensitive for lower input levels.
This makes it less useful if somebody wants an indicator for more than
one decade of signal level.

Input Volt. Meter current:
0mV -0.05uA
1mV 7.7uA
2mV 17.4uA
3mV 38.3uA
4mV 64.9uA
5mV 114.6uA

I have seen years ago this circuit.
http://www.reed-electronics.com/ednmag/contents/images/60701di.pdf
I am shure that this circuit will work at 40MHZ too, at least with a
HF-transistor. By the way, a higher resistor in the base makes it more
linear for lower levels. It will need an additional preamplifier too.

Overall it would make more sense to look for an integrated receiver IC
with a RSSI output. These ICs cover 60dB to 80dB dynamic range.
Google: rssi signal strength indicator IC
Hopefully somebody else can give an advice about a readily available
IC for 40MHz. There are many, but which of them is in reach for a
hobby project?

Best Regards,
Helmut

For that kind of range you are looking at an AGC servoing an amplifier
chain gain for constant detector output level- the AGC voltage is used
for signal strength indicator.
 
A

Active8

Jan 1, 1970
0
It's as conventional as they come. Common base configurations were used
a lot in the early days of transistors when you couldn't just go out and buy a
better transistor. Hell, there were only three or four different transistors at
all in the beginning. You needed to push the transistors as hard as you could
to get them to work at high frequencies. I remember GE taking out a large
magazine ad for one of their improved transistors that would actually oscillate
all the way up to the top end of the AM band at 1.5 megacycles.

Jim
You all have failed to mention one key feature of this design. The
common base config reduces the Miller effect capacitance.

HH,
Mike
 
J

Jim Thompson

Jan 1, 1970
0
Clever use of an inverted device!

...Jim Thompson

Until subjected to careful analysis.

Only good for quite small signal ranges :-(

...Jim Thompson
 
P

Paul Burridge

Jan 1, 1970
0
You all have failed to mention one key feature of this design. The
common base config reduces the Miller effect capacitance.

Good point. And BTW, I wasn't actually remarking on the CB config
aspect of it when I said it was unconventional. But each time I look
at it I can see a few more pieces of the jigsaw.
 
J

Jim Stockton

Jan 1, 1970
0
Fred said:
For that kind of range you are looking at an AGC servoing an amplifier
chain gain for constant detector output level- the AGC voltage is used
for signal strength indicator.

Check out the AD8307.
It's not too expensive.
Good Luck
Jim Stockton
 
J

James Meyer

Jan 1, 1970
0
You all have failed to mention one key feature of this design. The
common base config reduces the Miller effect capacitance.

HH,
Mike

I think somebody (forgive me for not remembering who) mentioned that
they were working on a cascode connected stage. That's common base derived and
one reason for cascode connections is to mitigate the Miller effect.

Jim
 
A

analog

Jan 1, 1970
0
Helmut said:
Hello "analog",

Howdy Helmut,
Always nice to see your posts.
your circuit is accidentally less sensitive for lower input levels.
This makes it less useful if somebody wants an indicator for more
than one decade of signal level.

True. It is just a starting point example for Paul B's benefit.
Input Volt. Meter current:
0mV -0.05uA
1mV 7.7uA
2mV 17.4uA
3mV 38.3uA
4mV 64.9uA
5mV 114.6uA

Here is what I got (voltages are rms):

Vin Iout
0.3mv 0.78ua (output increases
0.6mv 3.0ua almost as the
1.2mv 11.3ua square of the
2.4mv 36ua input within
4.0mv 101ua this region)
5mv 0.17ma
10mv 0.68ma
20mv 1.52ma (onset of limiting)
50mv 1.58ma
100mv 1.60ma (heavy limiting)

Although this is a very interesting circuit that very nearly makes
a transistor act like a zero forward voltage drop diode (for small
signals anyway), and I wish I would have thought of it, this method
is not used at all in my circuit.

With something like this one could go almost directly to dc in the
first stage and then amplify and shape the rectified signal with
opamps.

By the way, I have updated my LTspice field strength meter circuit
a bit and have posted it in alt.binaries.schematics.electronic along
with some gifs of it and its output.

Here is just the LTspice schematic:

Version 4
SHEET 1 964 680
WIRE -880 32 -864 32
WIRE -784 32 -768 32
WIRE -288 -176 -512 -176
WIRE 656 -176 656 -96
WIRE 656 -32 656 64
WIRE 656 320 528 320
WIRE 0 320 -416 320
WIRE -672 32 -672 112
WIRE -672 32 -624 32
WIRE -400 32 -416 32
WIRE -288 32 -288 -32
WIRE -288 -176 0 -176
WIRE 0 -176 304 -176
WIRE -288 -112 -288 -176
WIRE -352 96 -352 128
WIRE -512 -112 -512 -176
WIRE -528 32 -512 32
WIRE -512 32 -496 32
WIRE -512 32 -512 -32
WIRE -672 288 -672 320
WIRE -576 96 -576 112
WIRE -592 112 -576 112
WIRE -576 128 -576 112
WIRE -672 112 -656 112
WIRE -432 32 -416 32
WIRE -416 32 -416 208
WIRE 656 240 656 320
WIRE 656 64 720 64
WIRE 0 288 0 320
WIRE -208 32 -192 32
WIRE -192 64 -192 32
WIRE -192 32 -144 32
WIRE 0 -16 0 -176
WIRE -192 144 -192 176
WIRE 0 208 0 176
WIRE 368 32 384 32
WIRE 400 64 400 32
WIRE 400 144 400 176
WIRE 304 -176 528 -176
WIRE -768 32 -752 32
WIRE 304 208 304 176
WIRE 304 -16 304 -176
WIRE 400 32 416 32
WIRE -192 176 -176 176
WIRE -112 176 -96 176
WIRE -192 176 -192 192
WIRE 304 288 304 320
WIRE 304 320 0 320
WIRE 304 176 320 176
WIRE 384 176 400 176
WIRE 400 176 400 192
WIRE 304 176 304 128
WIRE 0 128 16 128
WIRE 0 128 0 80
WIRE 304 128 304 80
WIRE 656 64 656 176
WIRE -272 32 -288 32
WIRE -288 32 -304 32
WIRE -416 288 -416 320
WIRE -416 320 -672 320
WIRE -672 112 -672 208
WIRE -688 32 -672 32
WIRE 656 -176 784 -176
WIRE 784 -176 784 -96
WIRE 784 -16 784 64
WIRE 784 320 656 320
WIRE 784 64 784 160
WIRE 720 64 720 80
WIRE 720 64 784 64
WIRE 784 240 784 320
WIRE 288 128 304 128
WIRE -96 32 -96 64
WIRE -96 128 -96 176
WIRE -96 32 -64 32
WIRE -96 176 0 176
WIRE 0 176 0 128
WIRE -144 32 -96 32
WIRE 16 128 96 128
WIRE 208 32 208 128
WIRE 208 128 288 128
WIRE 96 32 112 32
WIRE 192 32 208 32
WIRE 96 128 96 32
WIRE 96 128 128 128
WIRE 192 128 208 128
WIRE 528 -128 528 -176
WIRE 528 -176 656 -176
WIRE 528 16 528 320
WIRE 528 320 304 320
WIRE 416 -64 400 -64
WIRE 400 -64 400 32
WIRE 384 32 400 32
WIRE 496 -64 528 -64
WIRE 528 -64 528 -48
FLAG -880 32 0
FLAG -768 32 1
FLAG -672 32 2
FLAG -576 128 0
FLAG -352 128 0
FLAG -192 192 0
FLAG 400 192 0
FLAG 720 80 0
FLAG -512 32 3
FLAG -416 32 4
FLAG -288 32 5
FLAG -144 32 6
FLAG 16 128 7
FLAG 288 128 8
FLAG 384 32 9
FLAG 480 32 0
SYMBOL ind -528 -128 R0
WINDOW 0 40 32 Left 0
WINDOW 3 40 57 Left 0
WINDOW 39 40 80 Left 0
SYMATTR InstName L1
SYMATTR Value 1µ0
SYMATTR SpiceLine Rpar=2k Cpar=2p
SYMBOL npn -528 96 M270
WINDOW 0 80 48 VBottom 0
WINDOW 3 80 48 VTop 0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL cap -752 48 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName C1
SYMATTR Value 1n
SYMBOL cap -496 48 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName C2
SYMATTR Value 10p
SYMBOL res -688 192 R0
SYMATTR InstName R1
SYMATTR Value 1k0
SYMBOL diode -656 128 R270
WINDOW 0 -32 32 VTop 0
WINDOW 3 -32 32 VBottom 0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL voltage -768 32 M270
WINDOW 123 -32 56 VBottom 0
WINDOW 39 -57 56 VBottom 0
WINDOW 0 32 56 VTop 0
WINDOW 3 -80 56 VBottom 0
SYMATTR Value2 AC 1
SYMATTR SpiceLine Rser=33
SYMATTR InstName V1
SYMATTR Value SINE(0 {p} 40.5e6 50u)
SYMBOL npn -304 96 M270
WINDOW 0 80 48 VBottom 0
WINDOW 3 80 48 VTop 0
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL cap -208 16 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C3
SYMATTR Value 1n
SYMBOL res -432 192 R0
SYMATTR InstName R2
SYMATTR Value 1k0
SYMBOL npn -64 -16 R0
SYMATTR InstName Q3
SYMATTR Value 2N3904
SYMBOL res -208 48 R0
WINDOW 3 36 64 Left 0
SYMATTR Value 10k
SYMATTR InstName R3
SYMBOL npn 368 -16 M0
SYMATTR InstName Q4
SYMATTR Value 2N3904
SYMBOL cap 480 16 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C4
SYMATTR Value 1n
SYMBOL res 288 192 R0
WINDOW 0 -5 40 Right 0
WINDOW 3 -5 75 Right 0
SYMATTR InstName R6
SYMATTR Value 1k0
SYMBOL res 384 48 R0
WINDOW 0 -4 40 Right 0
WINDOW 3 -4 64 Right 0
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL cap -112 160 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C5
SYMATTR Value 10n
SYMBOL res -16 192 R0
SYMATTR InstName R5
SYMATTR Value 1k0
SYMBOL cap 384 160 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C6
SYMATTR Value 10n
SYMBOL Misc\\battery 784 -112 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 132 Left 0
SYMATTR SpiceLine Rser=1
SYMATTR InstName V2
SYMATTR Value 2.8V
SYMBOL Misc\\battery 784 144 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 132 Left 0
SYMATTR SpiceLine Rser=1
SYMATTR InstName V3
SYMATTR Value 2.8V
SYMBOL ind -304 -128 R0
WINDOW 0 40 32 Left 0
WINDOW 3 40 57 Left 0
WINDOW 39 40 80 Left 0
SYMATTR InstName L2
SYMATTR Value 1µ0
SYMATTR SpiceLine Rpar=2k Cpar=2p
SYMBOL cap 640 -96 R0
SYMATTR InstName C7
SYMATTR Value 10n
SYMBOL cap 640 176 R0
SYMATTR InstName C8
SYMATTR Value 10n
SYMBOL ind 96 48 R270
WINDOW 0 32 56 VTop 0
WINDOW 3 5 56 VBottom 0
WINDOW 39 71 56 VCenter 0
SYMATTR InstName Lmeter
SYMATTR Value 10µ
SYMATTR SpiceLine Rser=380
SYMBOL diode -112 128 M180
WINDOW 0 36 40 Left 0
WINDOW 3 19 2 Left 0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL diode 128 112 M90
WINDOW 0 0 24 VBottom 0
WINDOW 3 32 24 VTop 0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL res 512 -80 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R7
SYMATTR Value 330k
SYMBOL res 512 -144 R0
WINDOW 3 36 64 Left 0
SYMATTR Value {100k*a}
SYMATTR InstName R8a
SYMBOL res 512 -80 R0
WINDOW 3 36 64 Left 0
SYMATTR Value {100k*b}
SYMATTR InstName R8b
TEXT -944 304 Left 0 !.tran 0 100u 0 .1u
TEXT -944 272 Left 0 !.ac dec 101 1e6 1e9
TEXT 528 -232 Center 0 ;.step param n list 0 .5 1
TEXT 152 -48 Center 0 ;100ua Full Scale
TEXT 528 -208 Center 0 !.param n=.512 a=limit(n,.999,1m) b=1-a
TEXT 528 -256 Center 0 ;Meter Offset Adjustment
TEXT -824 144 Top 0 !.param p=sqrt(2)*rms
TEXT -944 240 Left 0 !.param rms=4m
TEXT -656 -224 Top 0 ;Vin Iout\n_ 5mv 0.17ma\n10mv 0.68ma\n20mv 1.52ma\n50mv 1.58ma\n100mv 1.60ma
TEXT 0 -256 Center 0 ;FIELD STRENGTH METER
TEXT -832 -224 Top 0 ;Vin Iout\n_0.3mv 0.78ua\n0.6mv 3.0ua\n1.2mv 11.3ua\n2.4mv 36ua\n4.0mv 101ua
 
R

Roger Johansson

Jan 1, 1970
0
A chip called LM3189 (or 3089) can be used to build a nice field
strength meter.

Use the first half of the chip and take the output signal from pin 13
to a meter through a suitable resistor, as described in the National
Semiconductor datasheet for these circuits.

It gives indication from 10uVolt signal to around 1Volt signal.

It may be a bit too ambitious a project for mr. Burridge.
Im am not sure how easy it is to find this chip either.

But he should absolutely get the Handbook for radio amateurs from
ARRL. It is cheap to buy (considering its size and the enormous amount
of useful information) and it is available in most public libraries.

It contains, among all other things, descriptions of all kinds of DIY
measuring equipment related to radio and general electronics, and it
is written for people who don't have a lot of background knowledge in
electronics. The text is easy to understand and it has well checked
and tested circuits.
 
J

John Woodgate

Jan 1, 1970
0
Here is what I got (voltages are rms):

Vin Iout
0.3mv 0.78ua (output increases
0.6mv 3.0ua almost as the
1.2mv 11.3ua square of the
2.4mv 36ua input within
4.0mv 101ua this region)

That square-law response is normal for any junction rectifier at very
low input levels, including a diode rectifier.
 
K

Kevin Aylward

Jan 1, 1970
0
Active8 said:
You all have failed to mention one key feature of this design. The
common base config reduces the Miller effect capacitance.

But not necessarily as relevant as might be initially assumed. The
common base circuit is a bit more subtle than this. A fundamental reason
for the common base is the lower resistance at the emitter. This results
in a re.cbe limit, not an Rs.ccb limit (simplified). There is still the
same large gain from the emitter to collector, which still results in
miller gain to any capacitance from emitter to collector. This
capacitance may be less than the base-collector capacitance, but it is
still Miller amplified, but in this situation, the source resistance is
in || to rbe frequency response wise, so is not usually significant to
response. If the source resistance is low, Miller capacitance is not
relevant.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

That which is mostly observed, is that which replicates the most.
http://www.anasoft.co.uk/replicators/index.html
 
P

Paul Burridge

Jan 1, 1970
0
But not necessarily as relevant as might be initially assumed. The
common base circuit is a bit more subtle than this. A fundamental reason
for the common base is the lower resistance at the emitter. This results
in a re.cbe limit, not an Rs.ccb limit (simplified). There is still the
same large gain from the emitter to collector, which still results in
miller gain to any capacitance from emitter to collector. This
capacitance may be less than the base-collector capacitance, but it is
still Miller amplified, but in this situation, the source resistance is
in || to rbe frequency response wise, so is not usually significant to
response. If the source resistance is low, Miller capacitance is not
relevant.

Hi Kev. Have a good Christmas?
 
P

Paul Burridge

Jan 1, 1970
0
With something like this one could go almost directly to dc in the
first stage and then amplify and shape the rectified signal with
opamps.

ISTR somewhere that this *is* the preferred way of doing it. Saves on
RF transistors if nothing else! However one assumes at least *some*
degree of RF pre-amplification is needed to get a potentially very
weak signal beyond the knee of the diode characteristic.
By the way, I have updated my LTspice field strength meter circuit
a bit and have posted it in alt.binaries.schematics.electronic along
with some gifs of it and its output.

Here is just the LTspice schematic:

Thanks again; I'll check it out.
 

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