John (xrhonda91) and I have both used BAT-46 diodes to replace 1N34 diodes with excellent results. I've used the BAT-46 for AM detectors, and FM ratio detectors.

I recently found out about another low Vf Schottky diode, the 1N5819. The BAT-46 is a 100V small signal fast switching diode with a 6pf capacitance. The 1N5819 is a 1A 40V power rectifier with 110pf capacitance.

While the 1N5819 has a lower Vf, the BAT-46 performs better as an AM detector in my test radio. The 1N5819 weak signal audio level was about half of the BAT-46. I did not notice any difference with stronger stations.

I am curious if anyone else has tried the 1N5819 and how it compares to other diodes, as I've only tested it with one radio.

The Vf is slightly lower for the 1N5819 compared to the BAT-46 and 1N34a diodes I tested.

Nash---Thanks for the comparison results and diode specs ! Good to know that the BAT-46 is superior and don't have to wonder any longer about the 1N5819...

John

This has always been a mystery to me.

Since radio signals are in the range <100 mV, they are below the Vf or "cut in" voltage of these diodes. Detection seems to relate to other aspects of the diode's physics. All I know is that Ge and Schottky diodes are more sensitive than Si diodes.

The Schottky diodes are likely to have a larger chip area, resulting in more capacitance.

Rich

The biasing resistor of the first IF stage is usually applying bias to the detector diode, as these two stages are interconnected via the AGC circuitry. In fact, a 1N4148 will likely also work in these radios - the caveat is that the biasing conditions of the first IF stage will change.
The diodes can be overbiased in these simple receivers, so that "counter-biasing" was sometimes applied on the other side of the Ge detector diode to bring the biasing conditions back to where the diode was most efficient (see Sokol-403 schematic).

Diode curves aren't a sharp as commonly believed. Conduction may start a lot closer to zero than you might think. You can see this by placing a diode in series with your DMM and connecting to a variable voltage supply.

RRM

Hi all,

When John and I were experimenting with the FET Infinite Impedance AM detectors John told me about the BAT-46 so I ordered some from Mouser and then compared it to a germanium diode detector in one of my AM transistor radios . I was really amazed at the difference the BAT-46 diode made. I was now able to hear weak stations much loulder using the BAT-46.as a AM detector.

Something that could also be measured is the audio distortion added to the sig by each type of diode. This is one of the selling points for the schottky types, they add less distortion to the recovered audio. Biasing also might be tested. Also deriving a full wave detector setup for a given rig, for ensample there was/is a full wave rectification mod for the Icom R70 by replacing a resistor or cap in the detector circuit with a diode. Just some musings.

I read a article in the Sept 80 issue of ETI mag where they used a full wave AM detector with feedback to get hi-fi quality sound with very low distortion.