The transmission range of 0dbm output power

Dear All,
I have built an OFDM transmitter with 0dbm output power. If my
receiver needs 20 db of SNR to work properly, what would be the range
of my transmitter. The noise figure of the receiver is 5 dB. (In my
experiments, the range is roughly 2 feet. So i want to know if it is a
valid figure).

Thank you,

Aitezaz

On Apr 22, 9:42�am, aitezaz....@gmail.com wrote:
> Dear All,
> I have built an OFDM transmitter with 0dbm output power. If my
> receiver needs 20 db of SNR to work properly, what would be the range
> of my transmitter. The noise figure of the receiver is 5 dB. (In my
> experiments, the range is roughly 2 feet. So i want to know if it is a
> valid figure).
>
> Thank you,
>
> Aitezaz

Um.... depends on your channel and your front-end and a few other
factors.
Is it AWGN?  How many bits of ADC?  What is the analog front end gain?
Room temperature operations?

Julius

On Apr 22, 9:42�am, aitezaz....@gmail.com wrote:
> Dear All,
> I have built an OFDM transmitter with 0dbm output power. If my
> receiver needs 20 db of SNR to work properly, what would be the range
> of my transmitter. The noise figure of the receiver is 5 dB. (In my
> experiments, the range is roughly 2 feet. So i want to know if it is a
> valid figure).
>
> Thank you,
>
> Aitezaz

depends on a lot of things, such as the bandwidth of your signal, the
carrier frequency, antenna gains, ...for an 8MHz BW and 500MHz
carrier, it should be more like 1000 feet.

Google Friss Equation

Mark


Mark

On Apr 22, 9:42�am, aitezaz....@gmail.com wrote:
> Dear All,
> I have built an OFDM transmitter with 0dbm output power. If my
> receiver needs 20 db of SNR to work properly, what would be the range
> of my transmitter. The noise figure of the receiver is 5 dB. (In my
> experiments, the range is roughly 2 feet. So i want to know if it is a
> valid figure).
>
> Thank you,
>
> Aitezaz

It depends - what are your antenna gains (both Tx and Rx). A 1mW
(0dBm) laser can be seen from miles away if you are in the beam!  Plus
measuring at 2 feet is a near field measurement.  It is more common to
rate a receiver  by its sensitivity - i.e., minimum signal power into
the receiver.

Clay

On Wed, 22 Apr 2009 06:42:24 -0700 (PDT), aitezaz.abd@gmail.com wrote:

>Dear All,
>I have built an OFDM transmitter with 0dbm output power. If my
>receiver needs 20 db of SNR to work properly, what would be the range
>of my transmitter. The noise figure of the receiver is 5 dB. (In my
>experiments, the range is roughly 2 feet. So i want to know if it is a
>valid figure).
>
>Thank you,
>
>Aitezaz

To add a tiny bit to what's been said, research "link budget
analysis".

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org

Blog: http://www.dsprelated.com/blogs-1/hf/Eric_Jacobsen.php

Thanks for you people's replies. Here is the parameters that you
people has asked for,

Currently the channel is AWGN. The transmitter is exactly in front of
receiver but in an indoor environment. So, multipaths are likely but a
strong line of sight exists. ADC is 14 bit. Besides, the noise figure
of the receiver RF front end is 10 dB (in previous post i wrote 5 dB
that is incorrrect). The antenna gain is 2 dbi an omni directional
antenna both at TX and RX. Room temperature is 27 degree celcius.
bandwidth of the signal is 500kHz and on a carrier frequency of 430
MHz. I have used path loss equation but someone told me that this
equation is true for far field and my transmit power is so low that i
cannot use this equation. Besides, the path loss equation gives me a
transmit range of 2 km that it is not supporting at all. Almost 1 feet
away, the scatter plot of the receiver is perfect i.e. beautiful dots.
But, as soon as I increase the separation beyond 3 feet, the scatter
plot shows destruction.
Even a rough guess would be fine. I just want to make sure that this
much distance is justified.
Thank you again for your time.

On Apr 23, 12:57�am, aitezaz....@gmail.com wrote:
> Thanks for you people's replies. Here is the parameters that you
> people has asked for,
>
> Currently the channel is AWGN. The transmitter is exactly in front of
> receiver but in an indoor environment. So, multipaths are likely but a
> strong line of sight exists. ADC is 14 bit. Besides, the noise figure
> of the receiver RF front end is 10 dB (in previous post i wrote 5 dB
> that is incorrrect). The antenna gain is 2 dbi an omni directional
> antenna both at TX and RX. Room temperature is 27 degree celcius.
> bandwidth of the signal is 500kHz and on a carrier frequency of 430
> MHz. I have used path loss equation but someone told me that this
> equation is true for far field and my transmit power is so low that i
> cannot use this equation. Besides, the path loss equation gives me a
> transmit range of 2 km that it is not supporting at all. Almost 1 feet
> away, the scatter plot of the receiver is perfect i.e. beautiful dots.
> But, as soon as I increase the separation beyond 3 feet, the scatter
> plot shows destruction.
> Even a rough guess would be fine. I just want to make sure that this
> much distance is justified.
> Thank you again for your time.

yes you should be able to work over much more then 1 foot, at least
1000 feet

something is wrong with your implementation.  or there is interference
on your frequency

Mark

On Apr 22, 11:57�pm, aitezaz....@gmail.com wrote:
> Thanks for you people's replies. Here is the parameters that you
> people has asked for,
>
> Currently the channel is AWGN. The transmitter is exactly in front of
> receiver but in an indoor environment. So, multipaths are likely but a
> strong line of sight exists. ADC is 14 bit. Besides, the noise figure
> of the receiver RF front end is 10 dB (in previous post i wrote 5 dB
> that is incorrrect). The antenna gain is 2 dbi an omni directional
> antenna both at TX and RX. Room temperature is 27 degree celcius.
> bandwidth of the signal is 500kHz and on a carrier frequency of 430
> MHz. I have used path loss equation but someone told me that this
> equation is true for far field and my transmit power is so low that i
> cannot use this equation. Besides, the path loss equation gives me a
> transmit range of 2 km that it is not supporting at all. Almost 1 feet
> away, the scatter plot of the receiver is perfect i.e. beautiful dots.
> But, as soon as I increase the separation beyond 3 feet, the scatter
> plot shows destruction.
> Even a rough guess would be fine. I just want to make sure that this
> much distance is justified.
> Thank you again for your time.

How much power do you need at the input of your 14-bit ADC to produce
a full scale digital output? Also, make sure that your antennas and
input/output connections are impedance matched.

Darol Klawetter

On Apr 23, 11:41&#4294967295;pm, Darol Klawetter <darol.klawet...@l-3com.com>
wrote:
> On Apr 22, 11:57&#4294967295;pm, aitezaz....@gmail.com wrote:
>
>
>
> > Thanks for you people's replies. Here is the parameters that you
> > people has asked for,
>
> > Currently the channel is AWGN. The transmitter is exactly in front of
> > receiver but in an indoor environment. So, multipaths are likely but a
> > strong line of sight exists. ADC is 14 bit. Besides, the noise figure
> > of the receiver RF front end is 10 dB (in previous post i wrote 5 dB
> > that is incorrrect). The antenna gain is 2 dbi an omni directional
> > antenna both at TX and RX. Room temperature is 27 degree celcius.
> > bandwidth of the signal is 500kHz and on a carrier frequency of 430
> > MHz. I have used path loss equation but someone told me that this
> > equation is true for far field and my transmit power is so low that i
> > cannot use this equation. Besides, the path loss equation gives me a
> > transmit range of 2 km that it is not supporting at all. Almost 1 feet
> > away, the scatter plot of the receiver is perfect i.e. beautiful dots.
> > But, as soon as I increase the separation beyond 3 feet, the scatter
> > plot shows destruction.
> > Even a rough guess would be fine. I just want to make sure that this
> > much distance is justified.
> > Thank you again for your time.
>
> How much power do you need at the input of your 14-bit ADC to produce
> a full scale digital output? Also, make sure that your antennas and
> input/output connections are impedance matched.
>
> Darol Klawetter

there is a programmable amplifier before signal is fed to ADC. So, I
dont know the figures of ADC but the input to ADC + amplifier is
around 200 mVpp. Another thing to mention is that 0dBm is the power
that manufacturer gave me. I can control the DAC output gain as well
with the help of a programmable amplifier. But, when I increase the
gain of this amplifier beyond a point, the signal starts getting
distortion (may be because of the non-linearity of RF stage). So, I am
not operating my DAC with the maximum gain. Can I measure the output
power by removing my antenna on an oscilloscope or voltmeter as it
will give me the right figure.

Thanks

On Apr 24, 1:43�am, aitezaz....@gmail.com wrote:
> On Apr 23, 11:41&#4294967295;pm, Darol Klawetter <darol.klawet...@l-3com.com>
> wrote:


> > How much power do you need at the input of your 14-bit ADC to produce
> > a full scale digital output? Also, make sure that your antennas and
> > input/output connections are impedance matched.
>
> > Darol Klawetter
>
> there is a programmable amplifier before signal is fed to ADC. So, I
> dont know the figures of ADC but the input to ADC + amplifier is
> around 200 mVpp.

Check to see if you get a full-scale reading out of your ADC when your
transmitter is next to your receiver. If not, adjust your TX and RX
amplifiers until you do. Doing this will enable the full dynamic range
of your ADC, which you'll really need as you move the transmitter
farther away. Does your receiver have AGC?

Another poster suggested that you do a search on "link budget
analysis." Good idea. You need to understand the specs of all
components in the link.

> Another thing to mention is that 0dBm is the power
> that manufacturer gave me. I can control the DAC output gain as well
> with the help of a programmable amplifier. But, when I increase the
> gain of this amplifier beyond a point, the signal starts getting
> distortion (may be because of the non-linearity of RF stage). So, I am
> not operating my DAC with the maximum gain. Can I measure the output
> power by removing my antenna on an oscilloscope or voltmeter as it
> will give me the right figure.

Yes, you can. It would be easiest if you use an RMS volt/power meter.
Some of these meters have a power scale which is based on the input
impedance of the meter. If there's no power scale, just use the input
impedance (usually 50 ohms or 600 ohms) and voltage measurement to
compute power. If you don't have an RMS volt meter, then you'll need
to use an oscope (set for 50 ohms input impedance) and estimate the
RMS voltage if the scope doesn't calculate it for you (many digital
oscopes will make an RMS measurement).

Darol Klawetter