Why the input signal is divided by R2 and R3 to 9% ?
A very good question
We use two gain-adjustable amplifiers on the PCB that amplify 2 x 30dB ~ 1,000 times.
We could do with one amplifier, BUT we want to be able to regulate the entire range of 1-60dB.
Preamp gives too much signal even with a very small antenna, that's why.
You might ask, "why not a shorter antenna?"
Because the non-uniformity of component capacity would make the amplifiers too different.
As now, an antenna of 10cm/Ø 1.5mm, work the same on all amplifiers.
/richo
(2014-05-28, 18:07)RichoAnd Wrote: [ -> ]A very good question
We use two gain-adjustable amplifiers on the PCB that amplify 2 x 30dB ~ 1,000 times.
We could do with one amplifier, BUT we want to be able to regulate the entire range of 1-60dB.
Preamp gives too much signal even with a very small antenna, that's why.
You might ask, "why not a shorter antenna?"
Because the non-uniformity of component capacity would make the amplifiers too different.
As now, an antenna of 10cm/Ø 1.5mm, work the same on all amplifiers.
/richo
and what about the noise of IC1?
No problem in this situation.
Richo,
Are you saying that those of us building the Efield antenna should make the wire only 10 centimeters long?
That's a lot shorter than I'd heard initially, and need to carefully read the latest instructions if it is only 10 cm now.
Dale
(2014-05-28, 20:34)RichoAnd Wrote: [ -> ]No problem in this situation.
Hallo, RichoAnd
does this mean, by the antenna received noise is more than 10 times higher as the noise of the IC1?
Where does this noise come from?
(2014-05-28, 20:48)Dale.Reid Wrote: [ -> ]Richo,
Are you saying that those of us building the Efield antenna should make the wire only 10 centimeters long?
That's a lot shorter than I'd heard initially, and need to carefully read the latest instructions if it is only 10 cm now.
Dale
Dale, I don't think that's what he's saying at all. I think what he means is that a 10cm should perform about the same with any system, in similar locations and similar height above ground, and may be the optimum length for all, depending on wire gauge/diameter. I'm using a 37cm probe, which will likely prove too large as our US network grows, and I will likely trim it back... that's the cool thing about a wire probe.... cheap, easy to shorten if need be. I'd say anything longer than 37cm is definitely going to be too much probe overall, but with a wire, you can cut some off if needed!
I am still waiting for an explanation of the noise of an E field antenna and why the signal first gets divided by 10 and than multiplied up to 1000 times.
What is the origin of the noise?
thanks in advance
halder
I've answered in #2 and #4
The noise in IC1 is so low compared to the signal from the pre-amp that has no meaning.
(2014-06-07, 07:42)halder Wrote: [ -> ]I am still waiting for an explanation of the noise of an E field antenna and why the signal first gets divided by 10 and than multiplied up to 1000 times.
What is the origin of the noise?
thanks in advance
halder
The noise is all around, both man made (transmitters, motors, refrigerators, computers, car ignitions, etc)
And natural (distant thunderstorms, static buildup, earthquakes, volcanic action, solar radiation etc).
This is why the probe must be as remote from strong noise sources as possible, and also why the signal is attenuated first, we are only interested in the relatively strong signal from lightning, even after attenuation the noise is still much greater than the noise produced by the op-amp.
Ben.