long distance cell phone detector

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tank you, your answer was helpful, how can I use my so small amplifier?
 

000SHREDDER000 said:
tank you, your answer was helpful, how can I use my so small amplifier?
Click to expand...

Hi,

Do some yoga or other deep relaxation technique before attempting to solder, PTSD to be expected post-soldering, that's normal... Practice a few times on something tiny, and worthless, e.g. SMD resistors.

Do you have a good magnifying glass of any kind and suitable lighting? Microscope webcams are useful, I believe. Those illuminated large magnifiers look good, as do magnifying glasses (with fitted light, even better). What sort of soldering iron tip are you using, or is it an IC that one of those hot-air guns is needed?

If you can do it with a soldering iron, on a PCB with ...silkscreen/solder mask between pins, solder braid could be your friend. There are lots of (YouTube) videos about soldering SMD, all manner of pin designs, really helpful.

I accidentally bought some 10K 0603 resistors, they look like specks of pepper that I've avoided trying to solder by eye with a pencil-tip iron, so far - maybe they could go with your tiny IC .

Seriously, if you use it, practice a lot before attempting it, or just feel annoyed and get another that is a package size you can handle - I stick to SO8 as I doubt I could solder by hand much smaller than that.
 


First of all I must build a circuit board, IC itself is extremely small, I can't Imagine how can I do that even with a magnifier and a pencil tip, i think it needs a hot air gun with an special board, I don't know really, I uploaded a picture of IC here.

 

Hi,

I think that can be soldered with solder paste. Not a technique I am at all familiar with, have read about people who say they solder these parts in an oven or in a frying pan, I think both methods said they used sand (if I remember well...) as the layer between PCB and baking tray/pan.

SURFACE MOUNT NOMENCLATURE AND PACKAGING shows quite a few with their package names. Yours may be Leadless Chip Carrier, the datasheet will have the correct package name, then you can look for videos that show different ways to solder it. I have seen a video of a man soldering one with a fine-tipped iron, but it would still leave the pad on the bottom to be done by solder paste.

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This may be useful too it discusses soldering (reflow), but seems to have useful general information: QFN Package Users Guide Maybe that IC isn't LCC, maybe MICRO LEADFRAME PACKAGE (MLP), looking at the pictures.
 
The essential point is that the IC can hardly achieve it's performance without a specifically designed PCB.

The small package definitely serves a purpose with respect to the 10 GHz bandwidth, it's not there to annoy DIY circuit makers.

Believe me that this and similar packages can be almost easily soldered on a hot plate or using hot air.
 
I am back again :drevil:
Who can find this circuit problem?


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It is an FM detector, I didn't find any kind of problem in it, but still it doesn't work correctly.
 

The circuit itself doesn't look unreasonable but the simulation voltages are crazy.

The negative at the collector of the first transistor is probably due to rectification of your 2.0V input signal. I'm not sure what you think RF signal levels are in general but a cell phone say 10 metres away would probably produce less that 200uV at the antenna, thats 1,000,000 times less than you are applying!!

The input LC circuit will have a tuning range of about 1.0MHz to about 2.5MHz but you are applying 100MHz, that means almost all the input signal is shunted to ground and to achieve 2V at the antenna you are applying several Watts of power directly in to the antenna point!

If everything is working properly, you should have approximately 3V DC on each of the first three transistor collectors, the frequencies should all be the same (100MHz) and the AC signal level should increase at each stage.

Brian.
 


I know it's higher than the FM voltage but even in very little voltage the results are same,on the other side circuit doesn't work even without LC, I am confused again, here is a new simulation.


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here is a 200 uV input with correct LC resonant simulation.
 

This is actually an RF detector, it doesn't distinguish between AM and FM so the modulation of the signal source is unimportant.

The simulation still seems quite wrong to me. Intuitively, the circuit would work but the voltages the simulation produces are very wrong. I can only assume you have something configured wrongly in the simulator and that is why the voltages are unreasonable. Incidentally, the voltage at PR3 is DC, there shouldn't be any AC present and it has to be more than about 2V for all the LEDs to light up. There is a missing component, there should be another capacitor across the supply lines or 100nF or so but that wouldn't account for the wrong figures.

Brian.
 

Thank you for sharing your knowledge, I didn't adjust anything except the FM source, I will send an FM configuration picture below, I realized when I removed ground on both sides LED lights up but a simulation error occurred.
 

It looks like the SIM program is Multisim that knows nothing about electronics. There are no RF transistors, they are General Purpose and their collector resistor values are so high that stray and transistor capacitance reduces the RF gain to near zero.
I agree that there is no FM detector, the diodes make an envelope detector (AM).
 


You mean the simulator transistor values are incorrect?!,then why they put an FM source in the simulator,
also it has many kind of transistors, all are for general propose?!
 

"General purpose" transistors tend to be medium speed, medium power devices that can be used in many applications but for RF amplification they are not the best devices to use. Good high-frequency transistors would work far better but the underlying problem is the DC operating points are wrong. The collector voltages need to be near to half the supply voltage (~3V), when they are as low as 6.23mV there is no chance of them working properly.

There is a particular type of FM discriminator that uses a 'charge pump' with that kind of diode configuration but it relies on the base frequency being very low and on different values to the ones shown so it will not work as described. As Audioguru stated, with those values it should work as an envelope detector, giving an indication of received signal strength not the modulation index.

Brian.
 

Then I must to use another simulator ;-)
 

000SHREDDER000 said:
Then I must to use another simulator ;-)
Click to expand...
Another simulator program will simply show that the awful circuit is designed completely wrong, has the wrong parts and will not work.
The circuit needs RF transistors that are biased correctly. Like a radio it needs many LC tuned circuits so that it selects only the frequency you want. It must have automatic gain control so that it is very sensitive to weak stations but is not overloaded by strong stations. If you want it to play FM radio then it must have an FM detector.
 

Tank you for your answer,
I want to correct this circuit, after changing transistors with RF ones, which base and parts are incorrect?
 

First, you must learn about how transistors work and how to properly bias them. Then you must learn about high frequency radio circuits. The person who designed that horrible circuit did not.
 


Two things to note:
1. it doesn't say it is an FM receiver, only that it covers 75MHz to 140MHz which includes the band used for domestic VHF FM broadcasts.
2. the voltages on the transistors are as expected but completely different to what your simulation shows.

Brian.
 

In my post #51 I said that the collector resistor values are too high. The schematic in this thread shows 47k ohms but the original project used 4k7 that is 4.7k (10 times less) which is one reason that the simulation shows wrong voltages.
This thread has a "general purpose" transistor as the fist one but the original project uses a real RF transistor.
EDIT: The antenna is tiny so that it does not become overloaded by strong local stations. It is designed to pickup the signal from a nearby very low power FM bug transmitter.
I did not look for more differences.
 
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