detector prototype

[badai]

thanks so much for helping me......... .......now i understand to use this software....and hopefully can improve better after this.....actually i can't get this component (BFR90A) in my local shop, i bought wrong component actually before this....another series (BFG90, BFQ28, BFR24, BFR49) also didn't find. what should i do now????

 

[audioguru2]

Hi Badai,
Transistors having that unique package and pinout are made for very high frequencies. I found one in a cheap cable-TV amplifier box.
Show the picture of the transistor at your local shop and they might have an equivalent one.
Otherwise, an ordinary general-purpose transistor like a BC547, 2N2222 or 2N3904 will work in this circuit up to about 200MHz. A BC594 will go higher. Their pinouts are all different.

What do you hope to detect with this project?
Using general-purpose transistors, it will probably detect a little FM transmitter up close, if it isn't overloaded by local radio and TV stations.

 

[MP1]

To complete the board layout, you can use a 2N3904. Then you can use any transistor with the same package type and pin out. You should get the data sheets and compare the transistors listed by audioguru and choose the closest one that is available to you.

Good to hear you have Eagle figured out!

MP

 

[badai]

where is R17? i didn't find it in circuit diagram but this component had been placed in layout board , is it missing?

this is my schematic circuit. can you check for me either right or not? i'm using pad 1(wirepad) to connect my antenna, is it right?

why my +ve and -ve(supply symbol) point not occur in my layout?

View attachment 36670

 

[badai]

i hope it can detect rf signal from cell phones. so up to 200MHz or 350Mhz it's okay for my circuit.

 

[audioguru2]

It looks like the author missed R17 on his schematic, from pin 12 to ground like R15 on the other side.

In my country, cell phones operate at GHz frequencies. A 300MHz 2N3904 won't work unless an operating cell phone is very close to it.

I don't know why you re-drew the schematic without using opamp symbols.

EDIT (Mar 7/05): I said R23 when I meant R15.

 

[audioguru2]

BTW, the circuit doesn't have a negative supply, just a single 9V battery. The terminal labelled "-9V" is very confusing.

Your 1N4148 detector diode also won't work at high RF frequencies. Didn't we discuss it before? Use a 1N34A germanium diode or equivalent instead.

 

[badai]

1- i just scatch back, is it like this you mean?

2- So if the phone operates up untill 1900MHz, which one is appropriate transistor(except BFR90A) from list you given?

3 - In my previous circuit ff i'm using pad 1(wirepad) to connect my antenna, is it will work for my antenna?

View attachment 36671

 

[audioguru2]

Hi Badai,
None of the "general purpose" common audio amplifier transistors that I have listed will work above about 200MHz to 300MHz.
To receive 1.9GHz, you need a microwave transistor better than the BRF90A, which can receive up to only about 1GHz.

The BRF90A has no gain at 6GHz, a little gain at 3GHz, a gain of about 2 at 1.5GHz and a gain of about 3 at 1GHz.

 

[MP1]

Badai,
In Eagle, you must choose the correct IC package for the ICs used. You should be able to find most common op-amp packages in the "Linear" library. The IC-Package library is there in case you cannot find something that works.
Pay close attention to vcc,vee,vdd, etc on the library package as this will be the name of your bus. Then when you want to connect the grounds of all components to this bus, it will be correct. There will be no connection shown on the schematic for the power lines of the IC package. They are automatically connected on the board layout.

Hmmm....maybe we should split this post and put some of it in the CAD forum. If you have more questions regarding Eagle, why not post them in the CAD area so others who perform a search will be able to find previous posts on the subject.

MP

 

[badai]

if that kind of problem, i hope it can detect up to 200MHz until 300MHz, so i can use 2N2222 in this circuit isn't?

 

[badai]

can you show me clearly which part i should place R17?

 

[badai]

this is my latest schematic but still missing R17....... :-\

View attachment 36676

 

[audioguru2]

Hi Badai,
I have added R17 to your schematic at the location the author has on his parts layout drawing. I have never seen a VCO circuit like that, so try it with and without R17. R17 probably limits its highest frequency, or turns it off without an input.

View attachment 36677

 

[badai]

how to calculate the cut-off frequency which has value 60Hz?

 

[audioguru2]

Hi Badai,
Why do you want a cutoff frequency as low as 60Hz with this very high frequency RF circuit? A circuit's cutoff frequency is defined as the frequency it begins its cutoff, where its output is down to 0.707 of its voltage at higher frequencies, nearly the same.
As the project's notes describe, it already has 60Hz rejection since its C4 and R7 have a cutoff frequency of 727KHz plus the high cutoff frequency of its C5 for which its load is difficult to determine.

The cutoff frequency for a series capacitor that is driven from an extremely low impedance, and the capacitor feeds a resistor to ground is:
One, divided by 2 times pi times R times C.

I round the calculation off slightly and make it much easier:
0.16, divided by R times C. ;D

 

[badai]

as in datasheet if i'm using 2N2222 as my TR1, min. freq it will detect is 250MHz, so what is the maximum frequency(frequency range)?

 

[audioguru2]

Hi Badai,
A 2N2222 won't detect 250MHz very well. :'(
Its minimum Ft rating of 250MHz only guarantees that it will have a tiny amount of gain at 100MHz, just enough gain to work as an oscillator or mixer at 100MHz.
The Ft rating is the frequency at which the gain is only one, like a piece of wire.

Additionally, the Ft rating uses a transistor voltage of 20V, where its capacitance is low. With the project's 9V battery which drops to 6V over its life, the 2N2222 will have a voltage of about 3V and an Ft much lower than 250MHz.

You might be lucky and get a 2N2222 with an actual Ft of 300MHz at 20V. Then it would have a gain of 10dB up to maybe 80MHz in this project when its battery is 6V.

The project was designed for a microwave transistor with an Ft of 6GHz, and the circuit has a gain of 10dB up to 1GHz with it.

View attachment 36015

 

[badai]

so what minimum frequency it shoul be detect? How the VCO in this circuit is formed? Is it same like in tune radio circuit? :-\

 

[audioguru2]

Hi Badai,
I couldn't find out anything about your AA215 diode. Your 2N2222 transistor will have gain up to at least about 60MHz, no gain at about 180MHz and lose more signal at higher frequencies.

The VCO is an audio oscillator with no output at a very low detected signal level and a higher audio pitch with higher detected signal levels.