help with RF diode

[whiz115]

Hi!

i'm searching two diodes for one of my builds, with as low as possible resistance/impedance from 400MHz to 800MHz and one more from 800 to 2.4GHz for the second diode i don't care if it is low enough at 800MHz as long as it is at 2.4GHz.

150mA for forward Current and 25V reverse voltage are well above my needs! also if possible to be common diodes so i can locate them easily!

what are the specs for OA72? i can't find a complete datasheet.

thanks!

 

[RadioRon]

Can you describe what the application is? Sounds like you want PIN diodes, is that right?

 

[mvs sarma]

Hi!

i'm searching two diodes for one of my builds, with as low as possible resistance/impedance from 400MHz to 800MHz and one more from 800 to 2.4GHz for the second diode i don't care if it is low enough at 800MHz as long as it is at 2.4GHz.

150mA for forward Current and 25V reverse voltage are well above my needs! also if possible to be common diodes so i can locate them easily!

what are the specs for OA72? i can't find a complete datasheet.

thanks!

Try to Google for UHF signal diodes and for PIN diodes- the world will open up

 

[whiz115]

Can you describe what the application is? Sounds like you want PIN diodes, is that right?

it's for an RF receiver... guys simple germanium diodes like the OA72 you
think they are suitable for the frequencies i told you?

 

[Nigel Goodwin]

You don't mention what the diodes are doing in the radio, that's what you need to tell us!.

 

[mvs sarma]

it's for an RF receiver... guys simple germanium diodes like the OA72 you
think they are suitable for the frequencies i told you?

Hi wiz115,
please see in your ist post- you never mentioned receiver word. you said "one of my builds".
also, you sought the specs of 'OA72' . you have also commented " i can't find a complete datasheet."

So the reply comes to meet your needs.

I really don't understand your question mark in the post under reference.

try to co-relate.


Sarma

 

[RadioRon]

Whiz, I'm a bit puzzled. The reason is because there seems to be contradiction between your request for diodes for those frequency ranges of 400-800MHz and for 800-2400 MHz and for use in a receiver. Your reference to an OA72 is also contradictory to those frequencies, not to mention it is a very old germanium type which is to be avoided in most applications. Receivers usually downconvert to lower frequencies before detecting so a detector diode at those frequencies doesn't make sense. When you mention those frequencies, I assume that you want to switch or attenuate the signal using diodes, not detect it, in which case Silicon PIN or other would be better. There are times when you want to detect at these frequencies, I do admit, but these all involve measuring power, not receiving information. So, I wonder if you are asking for the wrong thing. One other application would be for a balanced mixer for downconverting from those frequencies.

Anyway, if you want a leaded detector diode for use at lower frequencies, such as is implied by your reference to the OA72, consider using BAT41, 42, 43 ...BAT48. I would not use a germanium device without a very good reason and these BAT4x series are not germanium, they are silicon schottky diodes suited to RF detection. If you want to detect power or do some mixing at those high frequencies that you mentioned, consider using a microwave schottky diode, perhaps an SMS3922 or the SMS1546 from Skyworks.

 

[Leftyretro]

Hi!

i'm searching two diodes for one of my builds, with as low as possible resistance/impedance from 400MHz to 800MHz and one more from 800 to 2.4GHz for the second diode i don't care if it is low enough at 800MHz as long as it is at 2.4GHz.

150mA for forward Current and 25V reverse voltage are well above my needs! also if possible to be common diodes so i can locate them easily!

what are the specs for OA72? i can't find a complete datasheet.

thanks!

As several people have stated it's hard to advice you without knowing what the function of the diodes in the receiver are. Just saying there for a receiver does not really help much. You did give frequency ranges and that helps somewhat.

If the diodes are being used as an attenuator then PIN diodes are the best choice but for a mixer then not. If used as a detector after an IF stage then high frequency diodes are not even a requirement. By the way 100ma is a pretty high current for a diode in RF application but there are some that can handle that current.

If you could post a circuit picture or link that would be the best was of getting help.

Lefty

 

[whiz115]

please see in your ist post- you never mentioned receiver word. you said "one of my builds".

There are times when you want to detect at these frequencies, I do admit, but these all involve measuring power, not receiving information. So, I wonder if you are asking for the wrong thing. One other application would be for a balanced mixer for downconverting from those frequencies.

sorry guys i couldn't imagine the details i gave weren't enough...

ok..."RF receiver" maybe it was misleading Radioron understood what i need. I want to detect and measure weak RF signals.

my build works on the same principle with that:

http://www.dl5neg.de/diodesensor/diodesensor.html

Radioron proposed "SMS3922 and SMS1546" are there any other i can use?

 

[JimB]

Why not just use the same diode (BAT62) which DL5NEG used in his article which you gave in the link?

JimB

 

[Nigel Goodwin]

ok..."RF receiver" maybe it was misleading Radioron understood what i need. I want to detect and measure weak RF signals.

A diode probe won't measure weak RF signals, the link you posted looks to be a direct connection from the output of a transmitter?.

 

[whiz115]

A diode probe won't measure weak RF signals

diode probe is?! a probe with a diode?

the link you posted looks to be a direct connection from the output of a transmitter?.

yes with this circuit it is supposed to measure the signal lever of a transmitter
i don't know if it sensitive enough so it can pick up a signal from distance...
i could try it with a small wire as an antenna ofc i'm going to build it with the components the site says...anyway!
that's why i want to build also something sensitive enough that i can have it only to detect electromagnetic waves in the frequencies i said before...

 

[mneary]

A power meter and a receiver for weak signals may appear similar to you, except for the million to one difference in sensitivity. There's also about a million to one difference in selectivity.

You should start looking at receiver designs instead of power meter designs.

 

[RadioRon]

yes with this circuit it is supposed to measure the signal lever of a transmitter
i don't know if it sensitive enough so it can pick up a signal from distance...
i could try it with a small wire as an antenna ofc i'm going to build it with the components the site says...anyway!
that's why i want to build also something sensitive enough that i can have it only to detect electromagnetic waves in the frequencies i said before...

A basic schottky diode detector using a good RF diode is usually sensitive down to about 0 dBm when well constructed but this depends on several factors, including how much attenuation is before the diode. This assumes that there is a tiny bit of DC bias current flowing in the diode to help move the operating point closer to its knee voltage. So, you can expect less sensitivity than this if not using any DC bias. The maximum input of the example circuit that you gave would be about 23 dBm before one of the input resistors fries.

In these frequency ranges, please avoid using a leaded diode, you must go with surface mount for good performance. The BAT62 looks like a good choice for up to 1 gHz at least, but I'm not sure how well it will work at 2.4GHz. Its worth a try. The data sheet for the Siemens BAT62 has curves showing the gain curve for a simple detector application, implying that you should get something useful a bit below 0 dBm, so I may be proven wrong about the claim of 0 dBm made above.

Here is another site that built a detector using a BAT62-03 :
http://pe2er.nl/

(look at the WiFi VSWR meter)
That unit is claimed to work up to 2.4 GHz.


Other diodes? Hmmm, will have to look around a bit more. Typically the BATxx series are not hard to buy.

 

[whiz115]

@Radioron so bat62 and batxx series can be my answer?

the site you gave me is very good... i found a schematic and
it is called "diode detector" is very simple!!! i like it...do you think i
can make it light a led when detects an electromagnetic field???


P.S i guess it works from a distance with a small antena it's not like
the device in the link i gave above.. right?

 

[RadioRon]

@Radioron so bat62 and batxx series can be my answer?

the site you gave me is very good... i found a schematic and
it is called "diode detector" is very simple!!! i like it...do you think i
can make it light a led when detects an electromagnetic field???


P.S i guess it works from a distance with a small antena it's not like
the device in the link i gave above.. right?

Yes, BAT62-03 is your answer.

Do you mean the "diode detector" diagram attached below?

This works a lot like the other link you gave, but with important differences. Both are intended to measure RF power, but this one has a preamp, that RF2320 IC, to take the signals from the antenna and boost them up to make them large enough to work with the diode. So this one will be more sensitive, perhaps too sensitive to cable directly to a transmitter, such as what you were thinking of doing. This one is better suited to use with an antenna as is shown.

This one uses two diodes in a voltage multiplier configuration, whereas the other one does not.

In either case, neither circuit will be able to light an LED from antenna signals as you need a lot of power for that and a diode detector will have trouble giving enough power. It could be made to do that by adding an amplifier after the diode part, based on a transistor or an op-amp.

BAT62-03 would work fine in either of these circuits I think. Other BATxx types might be OK too, but each one is a little bit different and when I look at a data sheet for one of these, I hope to see them say something like "suitable for RF detector at 1 GHz" or maybe "detector and mixer applications to 2 GHz" or something that describes that it is good to those high frequencies. Oh, and it must be a schottky diode.

 

[whiz115]

Radioron you're very helpful! the information you give me are very precious thanks!!!

perhaps you don't know that with a simple led and a rf diode you can make the most simple "rf detector!" (i just learned how to call it.. )
the problem is that such thing is not so sensitive...it is only helful to
detect electromagnetic fields from mobile phones!!! (i guess above 0,5-1W max power)

both the site i found and the one you gave me i think they are very interesting and i'm planning to build one of them... but do you think i can somehow convert the design in the link you gave me and build a simple rf detector that can detect the presence of an electromagnetic field and light a led without the drawback of the above circuit i described?

 

[RadioRon]

Radioron you're very helpful! the information you give me are very precious thanks!!!

perhaps you don't know that with a simple led and a rf diode you can make the most simple "rf detector!" (i just learned how to call it.. )
the problem is that such thing is not so sensitive...it is only helful to
detect electromagnetic fields from mobile phones!!! (i guess above 0,5-1W max power)

both the site i found and the one you gave me i think they are very interesting and i'm planning to build one of them... but do you think i can somehow convert the design in the link you gave me and build a simple rf detector that can detect the presence of an electromagnetic field and light a led without the drawback of the above circuit i described?

When visiting the far east about 7 years ago I saw many aftermarket antennas for mobile phones that have LEDs built in to the antenna and they would flash when the phone is transmitting. These were wire antennas that you would pull out of the phone, not so common anymore. Its all just for fun to have a flashing antenna, but it seems to me that if your always fighting for signal strength, like many users are, it doesn't make sense to waste a significant amount of it on lighting an LED. Not to mention that you are generating harmonic energy which will also reradiate. Sure it isn't much, but when us poor designers have to work so hard to get rid of harmonics and to make our phones radiate efficiently, it bugs me to go the opposite way just to have a cute little flashing light.

To answer your question, yes I think you can do it, but be prepared to add a battery to power the amplifiers that you will need, both the RF preamp that we saw already, and the DC amplifier that you will need between the detector diode and the LED.

 

[whiz115]

hehe nice... external antennas maybe disappeared but
the leds returned as stickers that you can stick in the back of the mobile phone!

something maybe irrelevant...one day many years back (maybe i was 10-12 years old), i was playing near a television antenna next to the antenna was a broken element, i took it and i connected it with an ammeter! which probably i got from something i had destroyed recently! then i aproached the antenna with it and the ammeter went crazy! i don't really know why i did that and how exactly i connected the ammeter with the broken antenna element.

i feel a bit shy now to say this... but what i had in mind is to improve what i did that period, i was thinking to rectify with an rf diode the signal and to use a ammeter (few uA) to detect weak rf signals! that's why i asked for rf diodes... then i thinked that it would be nice if i could also use a led as happens with the small devices that are used on mobile phones.

By searching the next i discovered the site with the rf measure gadget...i thought that i was in the right road, i used a BAT41 and a BAT85 firstly to light a led with the electromagnetic field from the mobile phone but unfortunately they didn't worked! i only managed to light the led with an OA72then i understood that it is bit complicated for my level in electronics... and that weak RF signals can't be easily detected without an amplification circuit.

I