Is 1n34a suitable for RF detector?

Thread Starter

k1ng 1337

Joined Sep 11, 2020
118
Hi I am considering purchasing the only available germanium diode available at my local shops (NTE 1n34a point contact) for use in the detector stage of radio receiver.

The datasheet specifies a Vf of 1v(max) @ 5ma and provides no graphs and does not provide other parameters such as reverse recovery time. I've noticed datasheets from NTE (a common supplier in my area) always have very basic datasheets which appear to be missing parameters common in other manufacturers datasheets.

I assumed any germanium diode would be superior to a silicon regarding Vf for a detector stage.. the datasheet for the 1n34a says its meant for RF but I can't really distinguish it from a silicon via its datasheet.

I've included the datasheet, thoughts? And how might this compare to a diode such as 1n4148?
 

Attachments

Last edited:

crutschow

Joined Mar 14, 2008
28,204
A germanium diode will have a lower forward drop than silicon, so can detect with a lower level RF signal.
That 1V forward drop is given at a much higher current (5mA) than when being used as a detector.
At typical detection currents (less than a mA) it will have only a few hundred mV forward drop.

A small Schottky diode has similar or better characteristics and is often used for high signal frequency detection.

What is the IF/RF frequency you want to detect?
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
118
AM/FM. I do have 1n4159 and 1n4148 diodes on hand. Regarding the datasheet I included, what am I to make of missing parameters such as reverse recovery time? Given my options would you suggest the 1n34a as a good option for experimenting? They are $2.50 each and I've wondered for a while how well a germanium diodes and transistors performs in small signal applications..
 

crutschow

Joined Mar 14, 2008
28,204
what am I to make of missing parameters such as reverse recovery time?
Since they give the rectfication efficiency a 40MHz I assume it sufficiently fast for your application.
They are $2.50 each and I've wondered for a while how well a germanium diodes and transistors performs in small signal applications..
You might want to consider a small Schottky diode instead, since Ge diodes and transistors are obsolete and have no significant advantage over silicon.
 

DickCappels

Joined Aug 21, 2008
7,984
If you buy one, here is how to tell whether it is actually germanium.

I bought some Germanium 1N60 diodes on eBay but they appeared identical to the Shottky 1N60 diodes I had been buying from an authorized distributor. Nothing I could measure seemed to show much of a difference until I checked the forward voltage temperature coefficient across the diode.

The forward voltage of a Si diode will drop by about 2.1 mV/°C (negative temperature coefficient, NTC). For a Ge diode this NTC is a bit higher at 2.5 mV/°C.
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
118
Was the analysis of reverse leakage current any indicator? I found several sources saying a Ge diode will have a much larger leakage current.

And concerning diodes in general..

1) If the Ge 1n34a is a point contact diode (n type to metal junction) and a Shottky Si 1n5819 is also a n type to metal junction, why are their Vf of ~0.3 so close? Do Ge PN junction diodes exist and what might the Vf be?

2) Can the reverse recovery time of a PN junction diode be thought of as an additional junction capacitance as a result of the depletion layer created by the PN junction.. I read that n type to metal junction does not suffer from reverse recovery time or is negligible
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
118
If you buy one, here is how to tell whether it is actually germanium.

I bought some Germanium 1N60 diodes on eBay but they appeared identical to the Shottky 1N60 diodes I had been buying from an authorized distributor. Nothing I could measure seemed to show much of a difference until I checked the forward voltage temperature coefficient across the diode.

The forward voltage of a Si diode will drop by about 2.1 mV/°C (negative temperature coefficient, NTC). For a Ge diode this NTC is a bit higher at 2.5 mV/°C.
Was the analysis of reverse leakage current any indicator? I found several sources saying a Ge diode will have a much larger leakage current.



And concerning diodes in general..



1) If the Ge 1n34a is a point contact diode (n type to metal junction) and a Shottky Si 1n5819 is also a n type to metal junction, why are their Vf of ~0.3 so close? Do Ge PN junction diodes exist and what might the Vf be?

2) Can the reverse recovery time of a PN junction diode be thought of as an additional junction capacitance as a result of the depletion layer created by the PN junction? I read that n type to metal junction does not suffer from reverse recovery time or is negligible.
 

nsaspook

Joined Aug 27, 2009
8,907
Was the analysis of reverse leakage current any indicator? I found several sources saying a Ge diode will have a much larger leakage current.



And concerning diodes in general..



1) If the Ge 1n34a is a point contact diode (n type to metal junction) and a Shottky Si 1n5819 is also a n type to metal junction, why are their Vf of ~0.3 so close? Do Ge PN junction diodes exist and what might the Vf be?

2) Can the reverse recovery time of a PN junction diode be thought of as an additional junction capacitance as a result of the depletion layer created by the PN junction? I read that n type to metal junction does not suffer from reverse recovery time or is negligible.
There's mainly majority carriers in a Schottky (metal-semiconductor junction) diode so there's much fewer minority carriers to sweep away during reversals. This also means the junction is more ohmic, so the leakage current is higher than pn-junction diodes.

https://www.chu.berkeley.edu/wp-content/uploads/2020/01/Chenming-Hu_ch4-1.pdf
The second difference between a Schottky diode and a PN junction diode is
that the basic Schottky diode operation involves only the majority carriers (only
electrons in Fig. 4–39, for example). There can be negligible minority carrier
injection at the Schottky junction (depending on the barrier height). Negligible
injection of minority carriers also means negligible storage of excess minority
carriers (see Section 4.10). Therefore, Schottky diodes can operate at higher
frequencies than PN junction diodes
 
Top