Substitute for a Germanium Diode

[jonovid]

I recently discovered a circuit for testing the output of low power RC drown transmitters in the UHF band.
testing that the antenna was in tune. 
the circuit called for a germanium diode! this is not the first time I have come across this in an RF sniffer circuit.
So where do you get a germanium diode? not a shockley diode. 
where can you salvage genuine germanium diodes in today's electronics? 
are there any old or used consumer electronics that guarantee to have genuine germanium diodes in them?
vs waiting weeks for a package to arrive that maybe or may not be more shockley diodes. 
as Jaycar do not seem to stock them ether.

[RoGeorge]

Almost any diode will work, Ge or not.

[jonovid]

the RF sniffer circuit I was looking at
its says VHF but I may try to make it work on UHF

[David Hess]

Low barrier schottky diodes make pretty good replacements for germanium diodes.  Look for parts with low capacitance and low forward voltage drop.

The alternative I have used in the past to increase the sensitivity of silicon diodes when doing direct detection is to use two diodes in a bridge configuration with the RF applied to one side of the bridge and the other decoupled to ground with a capacitor.  This compensates for the forward voltage drop of the diodes.

Another thing I would try now is to use 2N3904 base-emitter junctions as diodes since they have better conductance and are faster than common silicon switching diodes.

[bob91343]

Germanium diodes are still available.  You can use 1N34 and 1N270 for instance.  I have a drawer full of them and use them to replace burned out diodes in power meters, probes, etc.

[notsob]

Try Aztronics in Adelaide aztronics.com.au

They once supplied the AHARS (Adelaide Hills Amateur Radio Society) VHF Antenna analyser kit. I have purchased 1N34A germanium diodes from them a long time ago. Their stock list has "please call" against 1N34A.

May be worth a try

[profdc9]

If you want a source of a large number of cheap schottky diodes, the diodes called "1N60" or "1N60P" on ebay/aliexpress can usually be had for 100 for 1.50 USD.  I have bought large numbers of these for projects on occasion.

[@rt]

I’ve made several working crystal radios with them, so I assume they are the real thing.

https://www.ebay.com.au/itm/10-PCS-GERMANIUM-DIODE-1N34A-DO-7-1N34-IN34A-S/192345843160?hash=item2cc8b4a5d8:g:F5sAAOSwuUlb1mCq

[cdev]

Diodes wont conduct unless the voltage is its junction voltage, silicon is (usually) around twice as high as germanium. For that reason a germanium diode makes a better RF detector, IMHO. An 1N34A will usually do.

Almost any diode will work, Ge or not.

[T3sl4co1l]

RB751S40T1G, RB751V40T1G, SDMK0340L-7-F look good.

Tim

[RadioNerd]

Depending on the desired power level I can recommend SMS7621 and SMS7630 schottky Diodes (digikey/mouser etc have them). They are pretty sensitive detector diodes more than fast enough for UHF work.

[cdev]

Why use these newer diodes preferentially as I have a bunch of 1n34s now? Is there a reason they are better?

[T3sl4co1l]

Point-contact diodes have quite high ESR due to the, well, point contact.  Small junction area.  Same thing that gives them low capacitance, but which planar diodes can improve upon in all respects.

If you don't happen to need performance factors in that range, no, absolutely nothing wrong with them.

Tim

[cdev]

Do any other diodes have a lower voltage drop? (and act as a more ideal 'detector'?)

[Grandchuck]

"Infineon RF Schottky diodes are silicon low barrier N-type devices and, unlike other solutions available in the market, they come with various junction diode configurations which can be used for very sensitive power detector circuits, in sampling circuits or in mixer circuits. The very low barrier height and very small forward voltage, along with low junction capacitance, make this series of devices excellent choice as detector functions at frequencies as high as 24 GHz"

Google will turn up lots of info about Shottkys

[ignilux]

Speaking of "ideal detectors", you might find this old HP app note on zero bias schottky diodes interesting.

[grouchobyte]

I use these all the time for this. Cheap and not overkill

https://docs.broadcom.com/doc/AV02-1320EN

Bob

[djidji]

Do any other diodes have a lower voltage drop? (and act as a more ideal 'detector'?)

1N21D

[bob91343]

An amazing guy.

https://en.wikipedia.org/wiki/Walter_H._Schottky