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

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

Another source for microwave semiconductors is California Eastern
Laboratories. I think they are a division of NEC. See www.cel.com

Tam/WB2TT

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.

Ok I looked through the Agilent website and found what I think is the
proper diode. An HSMS-2852 two diode in series pack 3 pin surface
mount. However I noticed that the specs say it is best below 1.5ghz
and recomends the HSMS-282X Series for below 4ghz and above -20dBm.

In either case I can't find a place to purchase any of them in
quantities of less than 100. I can't seem to cross reference them to
anything that digikey carries. Quantities of 10 or 20 wouldn't be bad
but 100 at $.90/per is a little much.


I also found these other possibilities
HSCH-3486
ASI-3486
MA4E928B-54

(Robert) wrote in message . com...
....
Ok I looked through the Agilent website and found what I think is the
proper diode. An HSMS-2852 two diode in series pack 3 pin surface
mount. However I noticed that the specs say it is best below 1.5ghz
and recomends the HSMS-282X Series for below 4ghz and above -20dBm.

In either case I can't find a place to purchase any of them in
quantities of less than 100. I can't seem to cross reference them to
anything that digikey carries. Quantities of 10 or 20 wouldn't be bad
but 100 at $.90/per is a little much.

Yeah, that's a problem, I admit! :-) I generally just get samples of
small quantities. Tam posted another site to check out. And I'd
expect that Philips and some others have some decent GHz
detector-style Schottky diodes. You should be able to find some
vendor willing to sell you just a few of some appropriate diode. If
you have a way to check the response (a generator with calibrated
level, or even just step attenuators after a relatively uncalibrated
generator), you should be able to use diodes not necessarily optimal
for 2.5GHz, for a ratiometric application like SWR detection. By the
way, I think Agilent has one or more detector diode application notes
on their web site; they are in the data book anyway. They are worth
having a look at. Also, I'm not sure why you need two diodes...a
single diode should do the trick nicely. If that works for you, I
might be able to spare a couple HSMS-2850's, but I'd have to check how
many I have left.

Cheers,
Tom





I also found these other possibilities
HSCH-3486
ASI-3486
MA4E928B-54

Rob wrote:
"What would the equivalent diode be for up to 2.6GNz ?"
The microwave SWR meter page reference Rob gives says: "---a good
quality microwave diode would be used ---."

I recall using the venerable 1N23 for many microwave applications. My
ancient ECG Manual says that Sylvania`s ECG equivalent was 1N415C or
1N415E.

The 1N415C is tested at 9375 MHz for a maximum noise figure of 9,5 dB as
a mixer. The 1N415E is tested at 9375 MHz for a maximum noise figure of
7.5 dB as a mixer.

For a meter rectifier, you don`t care what the noise figure is, so
either diode would work just fine as the diodes are otherwise
equivalent.

A generic microwave silicon diode should be fine. The lower junction
voltage of a hot-carrier diode will allow greater sensitivity in a power
meter but may burn out more easily. The silicon diode will withstand 2
ergs.

Best regards, Richard Harrison, KB5WZI