Hi,
I m trying to amplify the voltage from a 433MHz flexi whip antenna which is connected on a strip board.
I have connected 5v supply to the antenna as shown in the schematic (..accident) ending with a circuit(on a stripboard) that works at 200MHz, 300MHz and sometimes 420MHz but not at 433MHz!!!!!
Any ideas whats going on with this circuit?
It is a surface mount part and the capacitors for bypassing the dc input and coupling RF in and out must also be surface mount parts mounted close to the IC. You can scratch out a board with a knife and small 1 inch by 1 inch scrap of copper board, but use double sided and ground the top to the bottom all around with copper tape.
The old, old 741 opamp was designed for amplifying DC. So they made its DC open loop gain about 200,000. To prevent it from oscillating with negative feedback added, they added a capacitor that cuts its gain above 2Hz at the rate of a loss of half per doubling of frequency until it doesn't have any gain (a gain of 1) at 1MHz. The output keeps dropping above 1MHz.
The capacitor also causes its max output to have slew-rate-limiting above 9kHz. The output at higher frequencies is converted to ramps like triangle waves and higher frequencies are reduced.
It doesn't matter if it is an inverting or a non-inverting amplifier. It is lousy at frequencies above only 9kHz.
National Semi makes the LM741 so I got their datasheet. Most other semi companies make a 741 and their datasheets are similar. I got it from www.google.com or from www.datasheetarchive.com .
National Semi makes the LM741 so I got their datasheet. Most other semi companies make a 741 and their datasheets are similar. I got it from www.google.com or from www.datasheetarchive.com .
I guess the 741 is so old that companies don't publish its full spec's anymore.
Try the datasheet for the uA741. I have it from TI and its frequency response graph is with dB's instead of thousands of times for its gain.
The 741 is still a crappy old antique - why would you want to be using just a device in the 21st century? - you can buy much higher spec devices for less money!.
In comparator mode your trying to use the full open loop gain (200,000 or so). It will perform terribly at 1MHz, you might end up with a low amplitude triangle wave. Some op-amps will work at 1MHz though, just look for high speed ones.
It doesn't, don't trust the sims . 400MHz is far too high for any op-amp, you need RF amplifiers or the best option, buying a ready made unit. Making anything for these frequencies on stripboard will not be sucessful, not at least without extreme care.
In comparator mode your trying to use the full open loop gain (200,000 or so). It will perform terribly at 1MHz, you might end up with a low amplitude triangle wave. Some op-amps will work at 1MHz though, just look for high speed ones.