RF transmitter with reduced power output

[Trishool]

transmitted power output

Hello guys,

Can anyone advise me the amount of RF power required by an 315MHz transmitter to just reach a distance of 10meter .

The sensitivity it requires for a receiver to hear no more than this 10 meter distance . I plan to degrade the modules performance to make it work as an RFID please bear with me.


Thanks in Adv

Ts

 

[FvM]

how does rf transmitter work

You can either specify a receiver sensitivity and ask for the transmitter power, or the other way round. But not modify both at the same time. And how the problem is related to RFID?

 

[Abhishekabs]

rfid output power

Hi Trishool.
The maximum transmitted power is limited by FCC rules.
What is the output power you are currently using?
Even 0dBm will also work.
Also regarding sensitivity,
What is your bandwidth?
If you check any IC in market they will usually say --110dBm for 10KHz bandwidth etc..

 

[Trishool]

rf transmitter power output

FvM,

You can either specify a receiver sensitivity and ask for the transmitter power, or the other way round. But not modify both at the same time. And how the problem is related to RFID?

Actually , I need to degarde the receiver inorder not to receive anything beyond that range and transmitter not to transmit anything beyond the specified range. This is to avoide crosstalk as I use indepandant Transmitter and receivers . The transmitter are always ON with their ID and I want not to allow other receiver which is out of their range get data from them . This is a mobile application with judgement to position of a Tag as well.


Abhishekabs,
Hi Trishool.
The maximum transmitted power is limited by FCC rules.
What is the output power you are currently using?
Even 0dBm will also work.
Also regarding sensitivity,
What is your bandwidth?
If you check any IC in market they will usually say --110dBm for 10KHz bandwidth etc..

Please see above , rules are not an issue here but the position localization of a transmitter .

Thanks for the help!
-Ts

 

[FvM]

rf power output vs distance

Actually , I need to degarde the receiver inorder not to receive anything beyond that range and transmitter not to transmit anything beyond the specified range. This is to avoide crosstalk as I use indepandant Transmitter and receivers.

It basically doesn't work this way.

You can use an arbitrary transmitter level between 0 and 10 dbm, and reduce the receiver sensitivity not to detect weak signals. If the transmitters are permanently on, you don't need to, cause the stronger signal is masking the weaker anyway. You should use rather FM than AM to get a better discrimination.
You should also consider, that e.g. in a building, the actual range is strongly affected by other parameters as multipath receiption. Also interfering sources may play an important role.

I want not to allow other receiver which is out of their range get data from them.

The most unrealistic idea of all.

 

[Trishool]

kenwood ts-680s rf output

Actually , I need to degarde the receiver inorder not to receive anything beyond that range and transmitter not to transmit anything beyond the specified range. This is to avoide crosstalk as I use indepandant Transmitter and receivers.

It basically doesn't work this way.

You can use an arbitrary transmitter level between 0 and 10 dbm, and reduce the receiver sensitivity not to detect weak signals. If the transmitters are permanently on, you don't need to, cause the stronger signal is masking the weaker anyway. You should use rather FM than AM to get a better discrimination.
You should also consider, that e.g. in a building, the actual range is strongly affected by other parameters as multipath receiption. Also interfering sources may play an important role.

I want not to allow other receiver which is out of their range get data from them.

The most unrealistic idea of all.

Hi FvM ,
Thanks ,do you have an idea but how much dB level is required for transmitter for a distance of 10meters (I have 315MHz/FSK/10dBm fixed power output transmitter) . Also what receiver sensitivity required for a distance of 10meter (the one I have has -112dBm )

Thanks
-Ts

 

[FvM]

rf transmitter expected range

A theoretical expression for the free space attenuation of a radio link, assuming isotropic antennas is

\[\alpha\] = 10*log(4\[\pi\]r/λo)² = 92.4 + 20*log (f/GHz) + 20*log (r/km) [in dB]

Antenna gain has to be considered additionally.

For 10m @ 315 MHz, the formula gives a rather low attenuation of about 42 dB.

Unfortunately, for the reasons already said, I don't expect that it will help you much in designing your radio link.

 

[Trishool]

rf transmitter distance

Unfortunately, for the reasons already said, I don't expect that it will help you much in designing your radio link.

Thanks for the help FvM actually , I do wanna make it as a micro power link as the range I require is low so principaly it should work with few trials . Please note this is how RFID works.



Thanks
-Ts

 

[FvM]

rfid distance output power

Please note this is how RFID works.

Yes and no. RFID applications have a specified operation volume, either the reader's receiving operation is sensitivity limited or the field supplying the tag falls below a minimum value at it's borders. But this doesn't imply, that the operation volume can be defined exactly and particularly separated from a neighbour reader without some overlapping zones.

I didn't hear a clear specification of your 10 m range. If it's a maximum range, in other words, no tag should be detected out of it's bounds, than a reliable operation range must be expected considerably smaller. Or the other way round, if it's a minimum operation range, than tags will be probably still detected in a larger distance.

I understand from your last post, that it's rather the first case. If the transmitters are operating in an intermitted mode (low duty cyccle), the best method to estimate their distance is a RSSI (field strength) information determined for each received packet.

 

[Trishool]

transmitters on reduced power

Please note this is how RFID works.

Yes and no. RFID applications have a specified operation volume, either the reader's receiving operation is sensitivity limited or the field supplying the tag falls below a minimum value at it's borders. But this doesn't imply, that the operation volume can be defined exactly and particularly separated from a neighbour reader without some overlapping zones.

I didn't hear a clear specification of your 10 m range. If it's a maximum range, in other words, no tag should be detected out of it's bounds, than a reliable operation range must be expected considerably smaller. Or the other way round, if it's a minimum operation range, than tags will be probably still detected in a larger distance.

I understand from your last post, that it's rather the first case. If the transmitters are operating in an intermitted mode (low duty cyccle), the best method to estimate their distance is a RSSI (field strength) information determined for each received packet.

RSSI is a problem here , my transmitter selected is a lowcost type and doesnt have RSSI . My effective range is about 3 meter most and I take the liberty for 10meters in the present case. I will keep atteunating it as much as possible to see where it fills the bill and will start from 30dBm. On the receiver side does an atteunator or a squelch ckt is required.

-Ts

 

[FvM]

10 meter rf transmitter

Assuming your protocol involves an error check with sufficiant hamming distance, no squelch should be needed to prevent erroneous data reception. But it may help to speed up synchronization to valid packets, depending on the receiver operation mode.