detector diode conduction question
 

Hello all,

I want to try to detect signal levels of 50mv to 200mv peak to peak.
I need a passive circuit with no amplifiers, and I will be feeding a
DVM with .01v resolution. The problem I am having is that a 1N34 will
not conduct very well at these low levels. Is there a more suitable
diode? Can you give me a part number, or a simple way to get just one
or two of these diodes? What the diode is looking at is a 50 ohm port
on a 30 to 60 mhz I.F. chassis.

Thank you for your time.

"gudmundur" wrote in message
...
Hello all,

I want to try to detect signal levels of 50mv to 200mv peak to peak.
I need a passive circuit with no amplifiers, and I will be feeding a
DVM with .01v resolution. The problem I am having is that a 1N34 will
not conduct very well at these low levels. Is there a more suitable
diode? Can you give me a part number, or a simple way to get just one
or two of these diodes? What the diode is looking at is a 50 ohm port
on a 30 to 60 mhz I.F. chassis.

This might be useful:

http://engphys.mcmaster.ca/~elmer101/sqlaw/sqlaw.html

Leon
--
Leon Heller, G1HSM
http://www.geocities.com/leon_heller

Behold, gudmundur scribed on tube chassis:

Hello all,

I want to try to detect signal levels of 50mv to 200mv peak to peak.
I need a passive circuit with no amplifiers, and I will be feeding a DVM
with .01v resolution. The problem I am having is that a 1N34 will not
conduct very well at these low levels. Is there a more suitable diode?

6AL5?

Just input from a tubehead ;-)

--
Gregg "t3h g33k"
http://geek.scorpiorising.ca
*Ratings are for transistors, tubes have guidelines*

Another method would be to transform the 50 ohm source impedance to
something higher before applying it to the detector. Each quadrupling of the
source impedance will double the RF voltage. This could be done with an RF
transformer, or a loosely coupled resonant tank circuit.

Joe
W3JDR


"Gregg" wrote in message
news:Q53Jd.48870$06.2762@clgrps12...
Behold, gudmundur scribed on tube chassis:

Hello all,

I want to try to detect signal levels of 50mv to 200mv peak to peak.
I need a passive circuit with no amplifiers, and I will be feeding a DVM
with .01v resolution. The problem I am having is that a 1N34 will not
conduct very well at these low levels. Is there a more suitable diode?

6AL5?

Just input from a tubehead ;-)

--
Gregg "t3h g33k"
http://geek.scorpiorising.ca
*Ratings are for transistors, tubes have guidelines*

gudmundur wrote:

Hello all,

I want to try to detect signal levels of 50mv to 200mv peak to peak.
I need a passive circuit with no amplifiers, and I will be feeding a
DVM with .01v resolution. The problem I am having is that a 1N34 will
not conduct very well at these low levels. Is there a more suitable
diode? Can you give me a part number, or a simple way to get just one
or two of these diodes? What the diode is looking at is a 50 ohm port
on a 30 to 60 mhz I.F. chassis.

Thank you for your time.

For peak voltage under 100 mV, tunnel diodes produce more output than
other diodes, but are hard to find.
http://www.americanmicrosemi.com/tut...unneldiode.htm
http://margo.student.utwente.nl/el/c...efaq.html#IV.3 - Tu
--
John Popelish

I want to try to detect signal levels of 50mv to 200mv peak to peak.
I need a passive circuit with no amplifiers, and I will be feeding a
DVM with .01v resolution. The problem I am having is that a 1N34 will
not conduct very well at these low levels. Is there a more suitable
diode? Can you give me a part number, or a simple way to get just one
or two of these diodes? What the diode is looking at is a 50 ohm port
on a 30 to 60 mhz I.F. chassis.

You can use "Zero-bias schotky diodes" for detecting small signals, but you
can also pass a small bias current through an ordinary diode to overcome the
forward conduction voltage.

On Tue, 25 Jan 2005 09:15:56 +0100, "Old Macdonald"
wrote:

I want to try to detect signal levels of 50mv to 200mv peak to peak.
I need a passive circuit with no amplifiers, and I will be feeding a
DVM with .01v resolution. The problem I am having is that a 1N34 will
not conduct very well at these low levels. Is there a more suitable
diode? Can you give me a part number, or a simple way to get just one
or two of these diodes? What the diode is looking at is a 50 ohm port
on a 30 to 60 mhz I.F. chassis.

You can use "Zero-bias schotky diodes" for detecting small signals, but you
can also pass a small bias current through an ordinary diode to overcome the
forward conduction voltage.


An 1N270 germanium diode is very good for the purpose - up to at least
1GHz. If linearity is interesting, it is easy to construct network to
keep accuracy withing 10% http://home.online.no/~la8ak/m2.htm

jm
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

If you have a fairly strong local broadcast station an auxiliary diode
receiver will create the DC bias voltage for the diode in your application.
That detector and your application can operate simultaneously.

Bill W0IYH

"gudmundur" wrote in message
...
Hello all,

I want to try to detect signal levels of 50mv to 200mv peak to peak.
I need a passive circuit with no amplifiers, and I will be feeding a
DVM with .01v resolution. The problem I am having is that a 1N34 will
not conduct very well at these low levels. Is there a more suitable
diode? Can you give me a part number, or a simple way to get just one
or two of these diodes? What the diode is looking at is a 50 ohm port
on a 30 to 60 mhz I.F. chassis.

Thank you for your time.

There really should be no problem detecting such large signals with an
unbiased diode. I use Agilent zero-bias Schottky detector diodes, but
your 1N34 should work about as well. The key is realizing that you
simply don't get much output from the diode detector at low input
levels, but I'm quite able to detect signals below 100uV -- yes, 100
microvolts -- with mine. Your signals are actually quite large, and
start to get into a transition region between response at low signal
levels, where the output voltage is proportional to input power level
(into a resistive load), and response at high signal levels, where the
output voltage is proportional to the input voltage. So you may need
to calibrate at several points. Be aware, too, that the response
depends on temperature. I believe you will be able to find some
application notes on the Agilent web site in the components section.

Although there are some really nice RF level detector ICs now from
places like Analog Devices and Linear Technology, a simple passive
diode detector can still be useful in many cases.

Cheers,
Tom

Ooops, in my first reply I missed that your DVM has only 0.01V
resolution. Wow! Even a 3.5 digit one at 2V FS resolves millivolts.
So to keep things passive, use an RF transformer to step up the voltage
to the detector diode(s). I trust your DVM has a high input
resistance, so the RF loading by the detector and its DVM load should
be quite small. You might be aided by using a voltage doubler scheme,
in addition to the transformer stepup.

Cheers,
Tom

gudmundur wrote:
Hello all,

I want to try to detect signal levels of 50mv to 200mv peak to peak.
I need a passive circuit with no amplifiers, and I will be feeding a
DVM with .01v resolution. The problem I am having is that a 1N34 will
not conduct very well at these low levels. Is there a more suitable
diode? Can you give me a part number, or a simple way to get just one
or two of these diodes? What the diode is looking at is a 50 ohm port
on a 30 to 60 mhz I.F. chassis.

Thank you for your time.