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What you mean as -75: 75 Ohm impedance or - 75 dBm received field ?
Anyway, with 1 W and considering a 0 dB antenna gain (TX + RX ), you have:
30 meters = 65 dB attenuation, meaning a signal on the receiver of - 35 dBm
500 meters = 90 dB attenuation, meaning a signal on the receiver of - 60 dBm
In both cases, unless you do not use a very very wide bandwidth, there is no problem with a receiver to receive such signals.
-75dBm is low for 1.5GHz.If you boost this receiver with a LNA, you can get -90-95dBm.
Increasing Output Power is worse than Improving the Sensitivity.
Another option is to use a directional antenna if it's applicable.
Calculations made by FANT are correct only under LOS (Line Of Sight) condition. This means if you have obstacle in between TX and RX antennas, or the antennas are quite low on the ground, the received signal will decrease.
In any case seems strange to me, that the RX sensitivity is only -75 dBm (even considering 5 MHz BW, NF of the receiver of 5 dB and an antenna gain of -10 dBi) you should receive signals as low as -92 dBm.
How did you measure the -75 dBm ?
Since the reception is based on the SNR, are you sure you don't have any interferer ?
I want to re-transmit it up to 500 meter. I have transmitter give 1 Watt at output ,what i have in mind that is:
1- put amplifier instead in cascade with device output.
2- this amplifier should have 0db in and 20db at outpt.
3- omni-directional antenna with 20 dB gain
I presume it's an exercise problem with a fictive constellation, not a real RF engineering problem.
1.+2. Amplifying 1W by 20 dB means 100 W transmitter power. Feasible if the fictive amplifier can handle the output power and the RF regulations allow for it.
3. Antenna gain is linked to directivity. A 20 dB omnidirectional antenna could be made as collinear dipole array (many vertically stacked dipoles), but it's not very practical.
1- You mean add an extra amplifier after the one you already have ?
2- Not clear. You mean 0 dBm input 20 dBm output (that is 100 mW) ?
In this case you will reduce the output power already have. Or 20 dB is the gain of the cascaded amplifier, as presumed by FvM ?
3- It's quite impossible to realize such high gain omni antenna (20 dBi). A (ideal) collinear would require 63 stacked dipoles !
Sir My problem,I have device transmit signal up to 30 meter, output power at antenna input is :1W,antenna said -75dbm omnidirectional (signal strength @30 meter). all that at 1.5GHz.
All i need is how to increase range up to 500 meter, to have signal strength=-75dbm @500 meter. all that at 1.5GHz.
If you are in perfect LOS (Line Of Sigth) you will need 20*log10(500/30)=24.4 dB more EIRP. To have this improvement, you can increase the power using an external amplifier, increase the gain of the antenna or both.
In case you want to only add an external amplifier you will need a power of 30+24.4=54.4 dBm, that is 275 W.
Or you could try to increase the gain of your antenna using a 4 dipoles collinear. Roughly you could reach a gain of 6 dBi (taking into account some loss). In this case you will need an amplifier having a power output of: 30+24.4-6=48.4 dBm, that is about 70 W.
If you are in NLOS (Non Line Of Sigth), instead, you will need more power to reach 500 m. I suspect you are in NLOS, since -75 dBm @ 30 m, at a frequency of 1.5 GHz is a too low signal to be in LOS. Unless you have a very poor antenna.
1-I google for anteena, and i found " JF-3 Versatile, Multi-Band Antenna" . it said it is 27dB . Can i use it directly (connect it to my device)
2-A second solution :Can i use "ZHM 500-3000/50 MIL GRADE HIGH POWER" + "OA-141605-NF 1400MHz - 1600MHz 5dBi Omni Directional Outdor Antenna"
if you are transmitting with a full watt, and only getting to 30 meters, something is broken in the transmitter, or you have the worst receiver in the entire world.
CT-1088 EUR Plus 8 is a multiband jammer, thus I conclude you want to extend it's range to 500 m.
Although the solution has been basically given in this thread (high power amplifier or huge vertically stacked antenna array), I' m sure that jamming is among those illegal activities that should not be promoted by Edaboard.
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