1N5817 schottky

J

John

Guest
Hello,

I'm about to make a wideband rf sniffer using an op amp and a simple
detector front end feeding a capacitor and one of the inputs to the op amp.
I could bias the diode near conduction if it will help.

I have to hand a 1n5817 schottky diode which is claimed to have a low
forward voltage drop. While it's not exactly a signal diode will it do the
job? Our local electronics store (Maplins UK) is fairly crummy when it
comes to range of semiconductors. I could get a bat43, how about one of
those?

Any advice much appreciated.

Thanks.
 
John wrote:
Hello,

I'm about to make a wideband rf sniffer using an op amp and a simple
detector front end feeding a capacitor and one of the inputs to the op amp.
I could bias the diode near conduction if it will help.

I have to hand a 1n5817 schottky diode which is claimed to have a low
forward voltage drop. While it's not exactly a signal diode will it do the
job? Our local electronics store (Maplins UK) is fairly crummy when it
comes to range of semiconductors. I could get a bat43, how about one of
those?
Click to expand...
At low current, it is going to just act like a pretty big
capacitor. About 250 pF. See figure 4 on:
http://www.diodes.com/datasheets/ds23001.pdf

Ask for a 1N5711.
http://www.st.com/stonline/books/pdf/docs/3238.pdf

--
Regards,

John Popelish
 
On Fri, 19 Sep 2008 12:34:39 -0400, John Popelish wrote:

John wrote:
Hello,

I'm about to make a wideband rf sniffer using an op amp and a simple
detector front end feeding a capacitor and one of the inputs to the op
amp. I could bias the diode near conduction if it will help.

I have to hand a 1n5817 schottky diode which is claimed to have a low
forward voltage drop. While it's not exactly a signal diode will it do
the job? Our local electronics store (Maplins UK) is fairly crummy when
it comes to range of semiconductors. I could get a bat43, how about one
of those?

At low current, it is going to just act like a pretty big capacitor.
About 250 pF. See figure 4 on:
http://www.diodes.com/datasheets/ds23001.pdf

Ask for a 1N5711.
http://www.st.com/stonline/books/pdf/docs/3238.pdf
Click to expand...
Yeah, thanks.
 
On Fri, 19 Sep 2008 12:27:42 -0700, ggherold wrote:

On Sep 19, 12:22 pm, John <J...@nospam.thanks> wrote:
Hello,

I'm about to make a wideband rf sniffer using an op amp and a simple
detector front end feeding a capacitor and one of the inputs to the op
amp. I could bias the diode near conduction if it will help.

I have to hand a 1n5817 schottky diode which is claimed to have a low
forward voltage drop. While it's not exactly a signal diode will it do
the job? Our local electronics store (Maplins UK) is fairly crummy when
it comes to range of semiconductors. I could get a bat43, how about one
of those?

Any advice much appreciated.

Thanks.

"> I'm about to make a wideband rf sniffer using an op amp "

What RF frequencies are you looking for? What OPamp are you using. Your
typical opamp is not going to work at RF frequencies (10 - 100 MHz.)
Minicircuits makes some nice RF amplifiers that might work for you...
these cost a bit more than op-amps but for $60-$100 you can do alright.
George
Click to expand...
I can use any op amp within reason. The input to the op amp will be dc.
I want as wide a rf (Hz) range as is possible. Anyhow I think it's sorted
now. Thanks for your help.
 
On Sep 19, 12:22 pm, John <J...@nospam.thanks> wrote:
Hello,

I'm about to make a wideband rf sniffer using an op amp and a simple
detector front end feeding a capacitor and one of the inputs to the op amp.
I could bias the diode near conduction if it will help.

I have to hand a 1n5817 schottky diode which is claimed to have a low
forward voltage drop. While it's not exactly a signal diode will it do the
job? Our local electronics store (Maplins UK) is fairly crummy when it
comes to range of semiconductors. I could get a bat43, how about one of
those?

Any advice much appreciated.

Thanks.
Click to expand...
"> I'm about to make a wideband rf sniffer using an op amp "

What RF frequencies are you looking for? What OPamp are you using.
Your typical opamp is not going to work at RF frequencies (10 - 100
MHz.) Minicircuits makes some nice RF amplifiers that might work for
you... these cost a bit more than op-amps but for $60-$100 you can do
alright.
George
 
John wrote:
On Fri, 19 Sep 2008 12:27:42 -0700, ggherold wrote:


On Sep 19, 12:22 pm, John <J...@nospam.thanks> wrote:

Hello,

I'm about to make a wideband rf sniffer using an op amp and a simple
detector front end feeding a capacitor and one of the inputs to the op
amp. I could bias the diode near conduction if it will help.

I have to hand a 1n5817 schottky diode which is claimed to have a low
forward voltage drop. While it's not exactly a signal diode will it do
the job? Our local electronics store (Maplins UK) is fairly crummy when
it comes to range of semiconductors. I could get a bat43, how about one
of those?

Any advice much appreciated.

Thanks.

"> I'm about to make a wideband rf sniffer using an op amp "

What RF frequencies are you looking for? What OPamp are you using. Your
typical opamp is not going to work at RF frequencies (10 - 100 MHz.)
Minicircuits makes some nice RF amplifiers that might work for you...
these cost a bit more than op-amps but for $60-$100 you can do alright.
George


I can use any op amp within reason. The input to the op amp will be dc.
I want as wide a rf (Hz) range as is possible. Anyhow I think it's sorted
now. Thanks for your help.

I don't know what you have in mind for a design lay out how ever, I
Click to expand...
can say that bipolar op-amps tends to miss behave around R.F. Their basic
diode structure them self's tend to act as detectors and if subjected to
R.F. near by, they could give you side effects you were not planning on.

Assuming that you intend to have this DIODE close to the op-amp, I
thought you may want to know this when selecting your op-amp, shielding
and lay out.


http://webpages.charter.net/jamie_5"
 
On Fri, 19 Sep 2008 18:23:43 -0400, Jamie wrote:

John wrote:
On Fri, 19 Sep 2008 12:27:42 -0700, ggherold wrote:


On Sep 19, 12:22 pm, John <J...@nospam.thanks> wrote:

Hello,

I'm about to make a wideband rf sniffer using an op amp and a simple
detector front end feeding a capacitor and one of the inputs to the op
amp. I could bias the diode near conduction if it will help.

I have to hand a 1n5817 schottky diode which is claimed to have a low
forward voltage drop. While it's not exactly a signal diode will it do
the job? Our local electronics store (Maplins UK) is fairly crummy when
it comes to range of semiconductors. I could get a bat43, how about one
of those?

Any advice much appreciated.

Thanks.

"> I'm about to make a wideband rf sniffer using an op amp "

What RF frequencies are you looking for? What OPamp are you using. Your
typical opamp is not going to work at RF frequencies (10 - 100 MHz.)
Minicircuits makes some nice RF amplifiers that might work for you...
these cost a bit more than op-amps but for $60-$100 you can do alright.
George


I can use any op amp within reason. The input to the op amp will be dc.
I want as wide a rf (Hz) range as is possible. Anyhow I think it's
sorted now. Thanks for your help.

I don't know what you have in mind for a design lay out how ever, I
can say that bipolar op-amps tends to miss behave around R.F. Their basic
diode structure them self's tend to act as detectors and if subjected to
R.F. near by, they could give you side effects you were not planning on.

Assuming that you intend to have this DIODE close to the op-amp, I
thought you may want to know this when selecting your op-amp, shielding
and lay out.


http://webpages.charter.net/jamie_5"
Click to expand...
Yeah, ok, thanks. I have made at least 10 of them over the last 15
years and I've found a couple of problems with them, but like you said,
shielding and another one, temperature compensation can be considered.
 
On Sep 19, 9:22 am, John <J...@nospam.thanks> wrote:

I'm about to make a wideband rf sniffer using an op amp and a simple
detector front end feeding a capacitor and one of the inputs to the op amp.
...I have to hand a 1n5817 schottky diode
Click to expand...
Probably not the best idea, the 1N5817 is intended for LARGE currents,
and is accordingly going to take a lot of RF current before it reacts.

A transistor makes a good detector, just capacitor-couple the
RF to its base, use the op amp to average and amplify the
emitter current. You can get slightly fancy, use two transistors
and amplify the current difference with same DC bias on each.
Differencing two transistors gets rid of thermal drifts.
If the RF source is low impedance (like, a loop antenna?) you might
want to couple (direct or inductively) to the emitter instead of the
base,
and sense the collector current.

It might be amusing to connect a speaker to the amplifier output, and
see what AM station is strongest in your area...

Adding a tuned circuit will get you halfway to building a grid dip
meter...
 
On Mon, 22 Sep 2008 23:56:39 -0700, whit3rd wrote:

On Sep 19, 9:22 am, John <J...@nospam.thanks> wrote:


I'm about to make a wideband rf sniffer using an op amp and a simple
detector front end feeding a capacitor and one of the inputs to the op
amp. ...I have to hand a 1n5817 schottky diode

Probably not the best idea, the 1N5817 is intended for LARGE currents, and
is accordingly going to take a lot of RF current before it reacts.

A transistor makes a good detector, just capacitor-couple the RF to its
base, use the op amp to average and amplify the emitter current. You can
get slightly fancy, use two transistors and amplify the current difference
with same DC bias on each. Differencing two transistors gets rid of
thermal drifts. If the RF source is low impedance (like, a loop antenna?)
you might want to couple (direct or inductively) to the emitter instead of
the base,
and sense the collector current.

It might be amusing to connect a speaker to the amplifier output, and see
what AM station is strongest in your area...

Adding a tuned circuit will get you halfway to building a grid dip
meter...
Click to expand...
No, I am building a wide band rf sniffer - up to as high a frequency as I
can get. Also a transistor has to be biased otherwise the forward voltage
drop is too much (0.6) and the bias currents are too high for my
application. I am going to use a micropower op amp which can be left
switched on all the time, detecting, so to speak.

If I want to find out which am station is the strongest I'll build a
crystal set/whatever and if I want a grid-dip or a wave meter I'll build
one of those too.
 
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