Agilent makes a bunch of possible detector diodes. For example, the
HSMS-2850 series of diodes suggests a sensitivity of "up to 35mV/uW"
at 2.45GHz. So with a 20dB coupler and 10mW (+10dBm) excitation, 40dB
return loss would give you about .3mV out of the detector, plenty to
see on a typical 3.5 digit digital voltmeter on a 200mV range. You'd
be lucky to get your coupler to have "40dB directivity" (that is,
calibrated that accurately to 50 ohms) anyway, unless you have a good
50 ohm precision load to check with. Be careful with such diodes:
they have a very low reverse voltage breakdown, so you shouldn't put
more than about +10dBm directly into a detector built with one of
them. But you can use other Schottky RF diodes with higher breakdown
if you really need to handle higher powers. The Agilent web site
should have selection guides to give you other ideas, if needed.

Cheers,
Tom

(Robert) wrote in message . com...
bob wrote in message ...
Another approach would be to use directional couplers and diode
detectors to measure forward and reflected power. The combination of
low power and f2GHz means care is needed.

I found an article on building a directional coupler and two
detectors. The coupler is simple enough. I checked ebay but I
couldn't find anything in the frequency range that had two taps. The
problem I have is building the detector. This site has a hand drawn
schematic but lists the diode as a Marconi LMR Mixer diode, but not
what an equivalent part number would be that can be ordered.
http://www.frars.org.uk/cgi-bin/render.pl?pageid=1085
This is the hand drawn schematic
http://www.frars.org.uk/sessionconte...e-detector.JPG

What would an equivalent diode be for up to 2.6ghz?

Thanks
Rob