[ARC5] Some information...

[AKLDGUY .]

Diodes can be used in 2- or 4-unit configuration. In general, they need
critical impedance matching (to 50 ohms, assuming you're wanting to install
in tube equipment). They need high levels of BFO injection (+13 dBm or 20
mW). They have a conversion loss (5dB for 2-diode, 8dB for 4-diode). Their
parts count is low, 8-10 items including the diodes. Personal opinion - not
recommended for tube equipment due to need for critical impedance and level
matching involving the winding of toroid transformers.

JFETS are suitable for tube equipment. BFO injection can be to the source
resistor and about 0.8V RMS (6.5 mW into 100 ohm) is needed.

The dual gate MOSFET is even better. Injection voltage needed at gate 2 is
1V RMS (0.1 mW). With proper injection voltage and moderate signal level,
the device has excellent IMD characteristics. Parts count (from the
suggested circuit diagram) is 13 including the MOSFET, input and output
coupling capacitors and source bypass capacitors. No critical components.

The FET devices have conversion gain of several dB.

The MC1496 IC has a larger parts count at 19, but even worse is that it has
9 live pins that must be supported. Even if you mount it dead-bug style,
the peripheral components consume quite a lot of chassis real estate all
around it. On the other hand, a FET product detector layout is in an inline
fashion, like an amplifier stage. It can literally be supported by
soldering its source lead to its source resistor.

This information is a summary from the ARRL Handbook 1992 (hard copy).

Neil ZL1ANM

On Sat, Sep 14, 2019 at 2:57 PM David Stinson <arc5 at ix.netcom.com> wrote:

> Is there a more "modern" device available for use as a Product Detector
> which
> doesn't require as many external discrete parts?  Thanks.
>
>
>
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