Increasing Sensitivity of Antenna/Amplifier Circuit?

JeanneFRIES's picture

Offline

Joined: Jun 29, 2017

Replies: 5
Increasing Sensitivity of Antenna/Amplifier Circuit?
July 27, 2017 - 7:11am

Hello,

 

I need to boost the sensitivity of a circuit that uses a .22uf capacitor as antenna in a system that is detecting very high (between 700-950 mhz) frequencies. I am using a BC548 Transistor. Here is the video - https://www.youtube.com/watch?v=RwfgJM9719s

If I were to get the best quality transistors and capacitors would this make a noticeable difference? If I was to add an extra strip of wire to the circuit as an additional antenna would this make a difference? Do you have any other suggestions? Perhaps slightly varying the transistor?? 

 

I have looked at this website https://www.aktuellum.com/mobile/circuits/receiving/ but I cannot do the math required (I tried), any general rules of thumbs to go by?

 

PLEASE HELP!!

Thanks <3 

Aswinth Raj's picture

Offline

Joined: Aug 16, 2016

Replies: 912
Okay I believe the circuit
July 27, 2017 - 12:53pm

Okay I believe the circuit that you are trying to do is similar to this one

https://circuitdigest.com/electronic-circuits/cell-phone-detector-circuit

If I were to get the best quality transistors and capacitors would this make a noticeable difference?

No you wont find any noticeable difference. Just make sure your existing transistor is working properly.

If I was to add an extra strip of wire to the circuit as an additional antenna would this make a difference?

What are you using for your antenna now? Is it just a wire? If yes increasing the length of the wire and spiraling it or using a radio antenna will defiantly  affect the range of the circuit 

Do you have any other suggestions? 

Yes, I wonder what power supply you are using for this circuit. This circuit is very sensitive so make sure your supply is free from noise (Using a battery will solve the problem). If you are using a battery make sure it is in good health try replacing a new battery or use a 12V wall adapter with regulator and noise filter circuit. 

 

 

JeanneFRIES's picture

Offline

Joined: Jun 29, 2017

Replies: 5
Hummm, 
July 27, 2017 - 2:17pm

Hummm, 

 

so so I looked up some more schematics and I found people saying that a LC358 (I think don't quote me) would work better and bea stronger amp. 

 

While in the schematics for the above detector shows there being an antenna, i also read that the capacitors were actually acting as the antenna. Is this true? Does the piece of wire simply boost the distance? If this is the case, what about an antenna like the 3G/LTE sticker offered by Adafruit? 

 

I can get a similar schematic as the one above working when I fully turn on and off my cell phone and it is directly in place with the actual circuit. - I can't seem to get it to work for phone calls or text messages however. Any idea why? How MHz frequency changes from turning off vs sending/calling? 

So if indeed I am working on something close(ish) to the MHz for this circuit, how can I fine tune the signal to being a little higher? Which capacitors/resistors should I change and should they be higher/lower? If i need to add a pot/trimmer ... which one? I've looked all this stuff up but can't quite get the right answer it seems... 

 

thanks very much for your help!