Antenna Amplifier Noise Figure

On Sat, 27 Jun 2015 15:49:12 +0100, Jeff Gave us:

The answer to all your needs. Less is more. That Chef's Hat conglomeration is overkill.

In message , Jeff writes

But you have to be careful, as "noise factor" is a numerical ratio, and "noise figure" is in dB.

In the analogue cable TV world, the noise figure (in dB) can be looked at as the amount of noise power that (say) a real-world amplifier notionally has at its input in excess of that which would be generated from a perfect resistor as its source impedance.

As a rule-of-thumb, in a 4MHz vision bandwidth, a perfect 75 ohm resistor generates -59dBmV. [Subtract around 48dB if you want dBmW.]

The output of a noiseless amplifier would be -59dBmV + G, where G is the gain in DB.

The output of a real-world amplifier would be -59dBmV + NF + G, where N is the noise figure.

One method of measuring the noise figure is first to feed the amplifier first from a resistive source, and measure the output noise level. Next, feed the amplifier from a source containing a known amount of noise, and note the increase of output noise. The noise figure can then be calculated.

In practice, the noisy source is usually a calibrated noise meter*. The first reading is taken with the noise meter set at zero additional noise output, and then the noise output is increased until the amplifier output level rises by 3dB. This means that the noise meter is now contributing the same amount of noise as the amplifier, and the noise figure can be read directly from its output display. [This conveniently saves having to do any further calculations.]

...between its shoulders.

Only because of the processing gain in the system, noise is always related to the bandwidth.

The whole discussion has a strong scent of golden speaker leads of the audio fans. Just substitute Litz for the gloden leads / connectors.

Is the whole project for the new crystal sets?

And you believe everything that your government claims ?

The GPS DSSS signal is more than 1 MHz wide, so you could claim -30 dB SNR. However, after despreading, the signal is only 1 kHz wide and the data rate is only 50 bit/s wide. Thus, the SNR should be calculated at

...and under his comb-over.

Great way if you have a R&S SKTU!!

The normal way these days is the Y-factor method and uses a switchable noise source with a fixed known and calibrated Excess Noise Ratio (ENR). The noise power from the device is measured with the source on and off and the NF calculated from that ratio. That is how Noise figure test sets normally work.

Jeff

On Sun, 28 Jun 2015 06:48:13 -0400, JW Gave us:

Full head of hair here. Sounds like you looked in the mirror, asswipe.

Indeed it is. The '3dB rise' method is essentially a good dodge for engineers to avoid having to do any hard sums.

Which is sort-of what I said in the middle of my ramblings.

It should be relatively easy to conjure-up your own noise measuring machine by using an old-fashioned, high-gain, rather noisy, wideband amplifier as the noise source, and follow it with a switched (or calibrated variable) attenuator. If you know the amplifier noise figure, and its gain, you know how much output noise it will produce - although it would help if you can get a friendly guru to check.

For high noise levels and low attenuator settings, the noise is essentially inversely proportional to the attenuator setting, but if there's low noise and a lot of attenuation, the noise output becomes asymptotic to the basic noise floor of the noise generated in the attenuator itself (ie no matter how much attenuation you switch in, the noise doesn't get any lower).

That makes complete sense, furball for brains.

You're projecting again, Furball.

Can you two find another thread to post your silly insults in? Why don't you start a new thread all about how much you guys like to bicker?

It was a nice, informative discussion until those two showed up. Too bad.

No one is forcing you to read anything either of us write. If you don't like it, go away.

Pot->Kettle->Black

On Sun, 28 Jun 2015 20:17:17 -0400, Jerry Stuckle Gave us:

Wrong, Stucklett. Rickman has attacked no one.

ROFLMAO! Another troll heard from. And this is even a third grader - from the immature name calling. And one who can't read, either.

But then it's only what one expects from a no-name troll. How many other groups are you known for trolling? I found a half dozen in less than a minute...

Why not go back to sci.electronics.design? Or don't they want you, either?h

On Sun, 28 Jun 2015 23:05:40 -0400, Jerry Stuckle Gave us:

"ROFLMAO!"? Talk about third grade mentality. That stupid s*it was out ten years ago, child.

Nice try though, STUCKLETT. Bwuahahahahaa!

On Sun, 28 Jun 2015 23:05:40 -0400, Jerry Stuckle Gave us:

I have nine inches of respectability to go up in your wussy ass with, little girl.