400 MHz Antenna Problem

[Debdut]

I'm thinking of buying an antenna of this type - **broken link removed**
It will be at the output of a transmitter and the input of a receiver. The maximum distance between the transmitter & the receiver is 5 m.
I'm bad than a novice when it comes to electromagnetic transmission theory. So, please help me out or send me some references.
I want to know the following things -
1. What is the least power that the receiver section can detect and successfully amplify considering the LNA of the receiver has a gain of 5 to 10?
2. How can I calculate the power transmitted by the transmitted antenna considering least power received by the receiver antenna?
3. The output of the mixer is a sinusoid of frequency 400 MHz. Can the Power Amplifier before the antenna be class B or AB amplifier?

 

[jiripolivka]

I'm thinking of buying an antenna of this type - **broken link removed**
It will be at the output of a transmitter and the input of a receiver. The maximum distance between the transmitter & the receiver is 5 m.
I'm bad than a novice when it comes to electromagnetic transmission theory. So, please help me out or send me some references.
I want to know the following things -
1. What is the least power that the receiver section can detect and successfully amplify considering the LNA of the receiver has a gain of 5 to 10?
2. How can I calculate the power transmitted by the transmitted antenna considering least power received by the receiver antenna?
3. The output of the mixer is a sinusoid of frequency 400 MHz. Can the Power Amplifier before the antenna be class B or AB amplifier?

What you need is to learn how to design a radio link. Use the Friis' Equation to define the receiver input noise power for a required signal/noise ratio, then antenna gain and distance between antennas which defines propagation loss.
The last step is to define the ERP, equivalent Radiated Power from which the transmitter power is defined.
Noise bandwidth is defined by the spectrum width defined by the modulation signal.
So you need to find many more specifications before you can start calculating radio link parameters.

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For references, take any good book on radio communication. The good one is ARRL Radio Amateur's Handbook, any issue

 

[D.A.(Tony)Stewart]

To add to previous post... the omnidirectional horizontal path and the dead spot on vertical, yields a meagre gain of only 2dBi . 0dB isotropic or 0 dBi is for a theoretical spherical antenna.

This "rubber ducky" choice trades sensitivity with directional pattern or "Directivity Gain" It does not control the transmit level, path loss or Receiver Noise Figure., and is a poor choice for long range.

 

[jiripolivka]

To add to previous post... the omnidirectional horizontal path and the dead spot on vertical, yields a meagre gain of only 2dBi . 0dB isotropic or 0 dBi is for a theoretical spherical antenna.

This "rubber ducky" choice trades sensitivity with directional pattern or "Directivity Gain" It does not control the transmit level, path loss or Receiver Noise Figure., and is a poor choice for long range.

For the maximum distance of 5 m, you will need no antennas at all. At 400 MHz, a quarter-wave piece of wire can be used as antenna. You will need no LNA, only a RF modulator for your input signal, and possibly a RF detector for receiver.

If you transmit power is ~ 1 mW, this should work.
Use the opportunity to learn how a radio link should be designed.

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No power amplifier is needed, either.

 

[Debdut]

Thanks for the quick reply.
So, what is the noise level in CMOS at 400 MHz? Will the signal reaching the receiver be at least 50-100 time stronger than this noise level?

 

[D.A.(Tony)Stewart]

For the maximum distance of 5 m, you will need no antennas at all. At 400 MHz, a quarter-wave piece of wire can be used as antenna. You will need no LNA, only a RF modulator for your input signal, and possibly a RF detector for receiver.

If you transmit power is ~ 1 mW, this should work.
Use the opportunity to learn how a radio link should be designed.

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No power amplifier is needed, either.

I agree. I overlooked the 5m distance. :-o

The receiver must reject atmospheric noise from other sources of interference such as above FCC chart, unless you are inside a scren room like a Lingren Faraday cage.
The mixer does not output 400Mhz but rather the IF freq. and must have a suitable filter to improve SNR and reject adjacent band interference.


5m is considered near field and signal levels can drop 30dB from antenna to antenna due to impedance mismatch possibilities.

THe receiver quality will make all the difference much more than the antenna.

 

[jiripolivka]

The noise level (power) is given as

Pn = kTB,

where k is the Boltzmann constant, T is temperature in Kelvins, B bandwidth in Hz (not the carrier frequency).

In your case there will be no noise problem, but you so far failed to indicate the transmit power and signal bandwidth.

Run a simple test as I mentioned above, from it you will see if some modifications are needed.

 

[Debdut]

The experiment will take place inside a Lab. But there is no such room as you mentioned.

I calculated using the free-space path loss equation that for 5 m the loss in signal from the transmitter antenna to the receiver antenna is about 76 dB.
Considering the input power at the receiver antenna should be at least 0 dBm. Should the transmitter power amplifier pump (0 dBm + 76 dB) power to its antenna?

 

[volker@muehlhaus]

Considering the input power at the receiver antenna should be at least 0 dBm.

Sure? 76dBm = 46dbW = 40kW is used in large radio stations. Isn't this a bit too much for this simple task? Why do you want such a high level at the receiver? Normal receivers can operate with much smaller input levels.

Example here: https://www.maximintegrated.com/en/products/comms/wireless-rf/MAX1473.html
Input signal range is from -114dBm to 0dBm.

Also, my calculation of the path loss is different from yours. With the calculator below, assuming antennas with no gain (0dBi), the path loss is 40dB.




https://www.qsl.net/pa2ohh/jsffield.htm

 

[Debdut]

Thanks very much volker@muehlhaus.
Actually I mixed up the formulae for path loss in km and in meter.
I'll look in the IC that you posted. I really need to brush up my basics.