long distance cell phone detector

Thread Starter

000SHREDDER000

Joined Apr 9, 2017
49
Hello,

Have a look at the following circuit:
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Field_Strength_meter_3_level.gif

It uses a selective tuned input circuit, Q1,2 and 3 are RF amplifiers, then a detection takes place and then a level display.

The circuit comes from this page with a heap of RF circuits:
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Homebrew_RF_Circuit_Design_Ideas.htm

Bertus
It looks good, so I must test it, what is q3 type, and the frequency rang of detection?
 

bertus

Joined Apr 5, 2008
22,121
Hello,

As the link says, it are circuit ideas.
I think you can also use a BC547 over there.
For higher frequencies I would go for some BF types for Q2 and 3.

Bertus
 

Thread Starter

000SHREDDER000

Joined Apr 9, 2017
49
Hello,

As the link says, it are circuit ideas.
I think you can also use a BC547 over there.
For higher frequencies I would go for some BF types for Q2 and 3.

Bertus
This circuit detection range is around 100 mhz, what was your mean about BF?
Maybe BF transistors?
i want to find an amplifier transistor with near UHF band or higher , but they are so many.
 
Last edited:

Thread Starter

000SHREDDER000

Joined Apr 9, 2017
49
Hello,

Have a look at the following circuit:
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Field_Strength_meter_3_level.gif

It uses a selective tuned input circuit, Q1,2 and 3 are RF amplifiers, then a detection takes place and then a level display.

The circuit comes from this page with a heap of RF circuits:
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Homebrew_RF_Circuit_Design_Ideas.htm
Bertus
Here is the simulator results:
it doesn't work.
vb.PNG
 
Last edited:

bertus

Joined Apr 5, 2008
22,121
Hello,

The input is selective. L1, C8 and C9 will determine the most sensitive frequency.
When you remove them, the circuit will react on all frequencies.

Bertus
 

Thread Starter

000SHREDDER000

Joined Apr 9, 2017
49
This circuit won't work cuz 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.
 

ian field

Joined Oct 27, 2012
6,536
This circuit won't work cuz 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.
There's a microwave oven leakage detector in the last issue of EPE magazine.

The RF techniques will be somewhere near the required band, so tweaking for the right frequency shouldn't be too difficult.

Haven't got to that article yet, so don't know what's in it. Probably more bells & whistles than needed, but it might be some useful inspiration.
 

Thread Starter

000SHREDDER000

Joined Apr 9, 2017
49
There's a microwave oven leakage detector in the last issue of EPE magazine.

The RF techniques will be somewhere near the required band, so tweaking for the right frequency shouldn't be too difficult.

Haven't got to that article yet, so don't know what's in it. Probably more bells & whistles than needed, but it might be some useful inspiration.
What do you say about this:
http://www.talkingelectronics.com/projects/FieldStrengthMeterMkll/FieldStrengthII.html
 

ian field

Joined Oct 27, 2012
6,536
Unlikely to work even if you upgraded to transistors with high enough FT.

Your circuit construction needs to start looking something like the inside of a TV tuner.

TV tuner transistors might just about work, but UHF BJTs are comparatively rare nowadays - most use dual-gate MOSFETs.

Very old mobiles had power transistors that were good for 9GHz and were pretty robust for experimenting with. Modern ones are usually highly integrated - any RF transistors are tiny, hard to identify and a bit fragile.
 

Thread Starter

000SHREDDER000

Joined Apr 9, 2017
49
Unlikely to work even if you upgraded to transistors with high enough FT.

Your circuit construction needs to start looking something like the inside of a TV tuner.

TV tuner transistors might just about work, but UHF BJTs are comparatively rare nowadays - most use dual-gate MOSFETs.

Very old mobiles had power transistors that were good for 9GHz and were pretty robust for experimenting with. Modern ones are usually highly integrated - any RF transistors are tiny, hard to identify and a bit fragile.
I bought some of them it's about 3 mm I can't even see it.
 
Top