i want to know that the best receiver should detect how much power in dbm.
What do you mean by a (nice receiver)? What do you want to do exactly?
In practice, a good commercial TV receiver will correctly receive signals down to about -85 dBm at the antenna leads. But you can certainly achieve better results. This figure depends on receiver self noise, bandwidth, and temperature, so that results way down to -110 dBm and lower can also be achieved, either by adding cost to lower receiver self noise, or add cooling, and so on, or by reducing the bandwidth.
This paper gives a good presentation of the factors involved:
http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/rcvr_sen.pdf
The attached report should explain what you want to know... in terms of front-end receiver noise. After that, it's all about how your signal processing processes signal versus noise.
Technical Report Noise and Noise Figure for Radar Receivers
The thermal noise power over a bandwidth W Hz can be computed as
−174 + 10*log10(W) dBm
in room temperature. To that you can add the noise figure (amplification in the receiver hardware). For a "nice receiver" it would be, say, 3-6 dB
The minimum equivalent input noise for a receiver at room temperature (290K) is -174 dBm / Hz.
It is then possible to calculate the noise floor for the receiver:
Noise floor = -174 + NF + 10 log Bandwidth
Where NF is the noise figure
dBm is the power level expressed in decibels relative to one milliwatt.
Yes, I fully agree with the standard formula to measure the platform noise level in a radio receiver. However, as is expected in RF related measurements,the variation even in two receivers of same type can be striking.
I am citing some data for different receivers. (i) 802.11b @2.45GHz=(-65 to -70)dBm; (ii) [email protected]=(-69 to -63)dBm; (iii) GSM@900MHz=( -41 to -42)dBm
Such range variation is to be remembered for receiver design and measurements.
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