Microwave diode?

Have simple detector circuit that specifies 1N21B diode. That diode is 20-plus years old and obsolete. Looking for current equivalent, possibly (but
not necessarily) smt.
Are these useable in place of a 1N21B for 2.4 GHz detection?:
<http://tinyurl.com/6g62bu
<http://tinyurl.com/62fqnv
Suggestions welcome.
Thanks,
--
DaveC
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Those look good. Skyworks has some really nice low-barrier Schottky diodes. And they have a fabulous sample kit of schottkies and varactors, lots of parts.
Go for "low barrier" parts for unbiased low-level detection.
The best detectors are probably germanium back diodes, but expensive.
Several semi companies now make active detectors... LTC, ADI.
John
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Depends which "C-band" those spec sheets refer to: IEEE C-band is about 4 - 8Ghz, NATO C-band is about 0.5 - 1Ghz.
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Aian field wrote:

And of course ITU C-band is 190.0-197.2 THz.
Cheers,
Phil Hobbs
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1N5711. Worked in my decades-old 1L20 spectrum analyzer's front-end mixer.
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Is that similar to the 1N6264 ?
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On Mon, 1 Dec 2008 20:11:08 -0000, "ian field"

That's a big-junction, high-barrier part, OK for a UHF mixer. But with roughly 1.5 pF of zero-bias capacitance, it's not ideal as a detector at 2.4 GHz.
John
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My question was off topic - I simply wondered if the two were similar.
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On Mon, 1 Dec 2008 20:26:55 -0000, "ian field"

Sorry, wrong guy.
John
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Hello Dave,
Try bat15 (comes in various packages, single,dual, quad), low capacitance (0.35pF at 0V bias, that is far better then the general purpose hybrid schottky rectifiers, the specify them at, for example, -0.5V). Video resistance of about 100 kOhm, so you can use it as a zero bias detector when loaded with 1M Ohm or more.
When you want to detect higher voltages, try bat62. This one has some more capacitance, but still a fast diode, with 40V (yes, 40V) reverse voltage. Video resistance is also about 100 kOhms,
When you want high video bandwidth, you should bias them or use special zero bias detector diodes with low video resistance.
Best regards,
Wim PA3DJS www.tetech.nl Leave out abc, and the mail is OK.
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Thanks for all the input.
The project is this:
<http://www.atvinderby.co.uk/2.4Ghz_SWR_Meter.htm
To the person asking about form-factor: there isn't any. Well, there is concern about strain relief, so if I choose an smt part it should be soldered to a speck of pcb to provide relief.
I looked at the BAT62 part; the datasheets say "up to GHz frequencies", but no specified bw:
<http://www.datasheetcatalog.com/datasheets_pdf/B/A/T/6/BAT62-03W.shtml
Is this a good stand-in for the 1N21B?
Thanks,
--
DaveC
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DaveC ha escrito:

Hello,
As a zero bias detector, up to 1 GHz I prefer BAT62 over 1N5711. Capacitance is 0.65 pF max, while for 1n5711 it 2 pF (I thought). When you make sure DC load is 1 Mohm or more, you retrieve over 80% of detected EMK.
Do not use BAT62 in a mixer or high bias situation as the intrinsic resistance is rather high. This intrinsic resistance (200 Ohms) limits its usable frequency despite the low capacitance. When voltage to be detected is low (max 2V RF amplitude), a better choice is BAT15 (cap < 0.35pF, so it is closer to 1N21). Though BAT15 is a mixer diode (12 GHz), video resistance is not that high (100 kOhm).
When you make sure the load resistance >> video resistance (that is the diode resistance at zero bias), sensitivity is as good as sensitivity of special detector diodes up to many GHz. When you match the diode, sensitivity is really high.
The advantage of the special very low barrier detector diodes is that you can use them at zero bias with moderate load. So you don't need a high impedance input. Of course you can bias a normal diode to get low video resistance, but than DC output measurement becomes more difficult because of thermal aspects.
Best regards, Wim PA3DJS www.tetech.nl remove abc and you have a valid mail address.
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How much is a 1n21 or 1n23 (wrapped in the original foil) worth these days? I probably still have a couple in the parts cabinet that contains the germanium transistors.
John
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why suffer with that design , unless budget is super critical:
google " w1ghz power meter"
or http://www.w1ghz.org/QEX/A_UHF+_VSWR_Bridge.pdf
Steve Roberts
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