AM detector IC - available ?

[AlexResch]

For my superhet project I learned that a diode causes loss of sensitivity because of the voltage drop and that when biased into conduction it causes distortion. Is there an IC which fixes these problems ? At least between 3-30Mhz . I don't seem to find one.

[HB9EVI]

You can do synchronous demodulation; like for an SSB signal you add via a BFO the carrier to the signal; this has even an advantage in case of selective fading

[iMo]

For example
https://plus.google.com/102499654761048990073/posts/cEdxAhKBgYf

[PA0PBZ]

A superhet will have enough IF amplification to overcome the diode loss so no problem.

[iMo]

You can do synchronous demodulation; like for an SSB signal you add via a BFO the carrier to the signal; this has even an advantage in case of selective fading

Long time back I played with TAA661 as the synch detector, afaik.. The limiting IF amplifier re-created the carrier out of the IF and then it was mixed with the IF signal as well (in the same chip). Or something like that

[HB9EVI]

Ah yea, those were the days... they're still for sale on ebay.

however, PA0PBZ is also right; with a stable signal, there's no issue with the detector diode in a superhet

[AlexResch]

I think I saw something called "precision rectifier" and I thought something similar might exist for AM detection.

[iMo]

Ge diodes are the best for AM
Or use an SDR at the 455kHz.

[iMo]

I think I saw something called "precision rectifier" and I thought something similar might exist for AM detection.

There is no HIFI broadcasted at shortwaves. So no special need for a precision rectifier.

See also my above link with a NPN transistor detector (could be an JFET used in so called "infinite impedance detector" setup - http://sound.whsites.net/articles/am-radio.htm ).

PS: you may try with DMR on shortwaves..
https://en.wikipedia.org/wiki/Digital_Radio_Mondiale

[AlexResch]

I found this

http://amwindow.org/tech/htm/alowdisdet.htm

[HB9EVI]

wow, that's an effort! I'd call it overkill

[iMo]

Wire it with an oxygen free copper wire then for the best sound 
PS: Is there any AM broadcasting at SW? Afaik all stations I've tuned recently are English speaking far-east stations..

[AlexResch]

I don't understand your point. I do this to learn , I have no interest in SW "hi-fi". In general, I do not have any interest in HIFI at all.

[HB9EVI]

I'm also wondering what is your aim.

On one side, you want to use an overly complex AM detector, but when we were talking about the IF, you insisted on 455kHz, what is rather poor choice.

There would be a big benefit in a higher IF, but a rather low to practically non-existing benefit in that AM detector.

You see, what we mean?

[janoc]

Wire it with an oxygen free copper wire then for the best sound 
PS: Is there any AM broadcasting at SW? Afaik all stations I've tuned recently are English speaking far-east stations..

Quite a bit still. BBC World Service, Deutsche Welle, I have heard quite a bit of US-based talk radio too (mostly religious stuff). Also a lot of middle-Eastern stations can be heard here quite often.

[AlexResch]

I'm also wondering what is your aim.

On one side, you want to use an overly complex AM detector, but when we were talking about the IF, you insisted on 455kHz, what is rather poor choice.

There would be a big benefit in a higher IF, but a rather low to practically non-existing benefit in that AM detector.

You see, what we mean?

No, not really. This is a learning project for me . I already have 455Khz filters of various kinds and a couple of ( decent ) 455Khz receivers to compare with. Once done with this project I will move on and do a different IF. Also, 455Khz is easy to track and I have 30-340pf variable caps. I suspect a higher IF will not be as easy to track and I want to keep it simple. So simple that even with some failures and some detours I can do it for sure. 
I am a lot on an RC heli forum and I saw there the same thing - you ask a specific question and you get a lot of advise on how to do something else.

[HB9EVI]

Well, keep it simple is nice, but it's not simple anymore with a opamp full wave rectifier at RF.

[AlexResch]

Well, keep it simple is nice, but it's not simple anymore with a opamp full wave rectifier at RF.

That is for a ( much ) later stage. It's just me - I like to plan way ahead. First I'll do a simple Germanium diode detector.

[HB9EVI]

sounds reasonable...

it's a nice idea though, but I've never seen it implemented anywhere; taking into account the possible interferences on AM modulation and the propagation on SW, I'm not wondering

[BrianHG]

If you have a filter tank input, you can use a TV IF receiver IC.  They usually can operate between 15Mhz and 70Mhz, but, maybe you can go lower.  Depending on if you are decoding data VS audio, you'll need to adjust the AGC cap value.  Many also have a second FM 4-8Mhz internal IF which you wont need.

Example, TDA8340 / TDA8341 : https://www.bucek.name/pdf/tda8340,8341.pdf

You also get an automatic fine tuning output on this IC.

[BrianHG]

This is a weird one in a TO-92 package which is specked to 3Mhz, but, maybe you can stretch it more:

https://www.wiltronics.com.au/product/8202/ta7642-am-radio-i-c/

This one should do you entire frequency range: TEA5551T http://www.shfmicro.com/TEA5551T.pdf

This one has a complete I2C controlled digital tuner in an IC, minimal parts, 2.3 to 28.5Mhz: https://www.silabs.com/products/audio-and-radio/multi-band-radios/si4822-26-27-40-44-radio-receivers

[AlexResch]

This is a weird one in a TO-92 package which is specked to 3Mhz, but, maybe you can stretch it more:

https://www.wiltronics.com.au/product/8202/ta7642-am-radio-i-c/

This one should do you entire frequency range: TEA5551T http://www.shfmicro.com/TEA5551T.pdf

This one has a complete I2C controlled digital tuner in an IC, minimal parts, 2.3 to 28.5Mhz: https://www.silabs.com/products/audio-and-radio/multi-band-radios/si4822-26-27-40-44-radio-receivers

Thank you for the first one - news to me. Actually I collect those and have around 10 different radio IC's. Not digital ones - not my interest. Once I am finished with the present project in a couple of weeks I will try the TDA1046 from Siemens. Old IC but I was told it was very good on SW :

[bd139]

This is all too complicated.

The bog standard and boring 2N3904 is a very nice low noise AM detector in the emitter follower arrangement if you stick a small capacitor across the emitter resistor. BE diode is the detector and the really cool bit is the thing is forward biased by the base bias network which means it'll pick up really really low signal levels.

I found this out by accident when I was about 12.

[AlexResch]

This is all too complicated.

The bog standard and boring 2N3904 is a very nice low noise AM detector in the emitter follower arrangement if you stick a small capacitor across the emitter resistor. BE diode is the detector and the really cool bit is the thing is forward biased by the base bias network which means it'll pick up really really low signal levels.

I found this out by accident when I was about 12.

Thank you. I will definetely try it.

[bd139]

Quick LTspice simulation for you...



inductor isn't necessary but it kills a lot of the carrier going into the audio stage. Values not optimised. Lots of improvement possible