Simple radio transmitter

[yoelbn]

Hi
I want to build a radio transmitter that can transmit a code (like a serial number),
and a receiver that could receive the transmission and verify the code the transmitted code. The distance between the receiver and transmitter will be in a radius of 1Km approximately.
I am not a rf engineer, but I am an electrical engineer and I know the basic of rf transmitter/receiver.
Does anyone have a circuit to share with me, or does anyone knows if I can buy this kind of system.

 

[kam1787]

Maybe start with an RC transmitter and receiver

 

[yoelbn]

Could you elaborate?
Maybe you can find a circuit diagram?

 

[davenn]

this is one of many options
https://www.linxtechnologies.com/en/products/modules/lr-rf-transmitter-receiver

there's many more on google

Dave

 

[jiripolivka]

Could you elaborate?
Maybe you can find a circuit diagram?

If I understand, you actually look for a communication system that can transmit your data (not defined format and speed) over one kilometer distance, to a receiver with data output.

There are commercial transmitters and receivers but you also need a pair of antennas and you should give an information about the signal path from the transmitter and receiver (obstacles, other possible interfering signals along the path).

In many countries there are legal regulations for installing such system.
Best try to find a radio amateur or a group who will know better so you do not need to start from a scratch and get caught in problems.

 

[yoelbn]

Hi Dave,
I found some parts that might fit but the one you gave me seems to be O.K.
The problem is that I want to evaluate it before I jump in the deep water, and for that I will need somthing like an evaluation kit wich is a little expensive.
If I would like to build it myself with wires and circuit board matrix or somthing like that, but I am not sure how it will affect the end result.
What would you recommend? Buy ev-kit or go to the DIY approch?

 

[Tomsin yin]

u can find some examples on ADS！

 

[D.A.(Tony)Stewart]

1st you must decide if there is a power limitation and do you have to turn off the transmitter between bursts, then is it one to one to many to one or many to many data points.

Thus simple AM works well with AGC or continuous carrier then modulated using either positive or negative logic, so you can decide this . Easy is UART Start bit to trigger AGC in receiver for variable path loss, then data bits and stop bit with parity for reliability.

FM is more reliable if f deviation to signal rate is high. ( FM improvement factor increases with square root of ratio for CNR to SNR conversion in dB.

Then PM and n level or QPSK or QAM is more efficient and even more efficient when 64 levels instead of 4 or even 128 but it requires higher SNR to receive according to Shannon's Law.

So you can choose simple positive logic AM asynchronous method and many cheap solutions exist .
With FM when no signal is received it must be squelched to prevent noise but often gives cleaner signal like FM radio if 75kHz deviation for stereo bandwidth of 15kHz each.

AM radios are 7kHz bandwidth and telephone cordless are usually >=4kHz

RFID's are usually ASK or amplitude shift key ( AM async burst ) sending serial number.

Every AGC has different response times according to design, so there are many protocols for different applications and different data rates. ( hundreds of standard and proprietary protocols from VLF to UHF & microwave)


Cheap and dirty solution is LC filter oscillator keyed on/off and LC filter receiver with AGC amp and comparator.

better solution is use existing radio parts or X-2 radio units for home remote control or garage door openers with relays. ( $10) just modify for your purpose.

If you want long haul distance.. consider license free SW band which goes further than ISM or microwave band

If you want to really long distance,,.. use big satellite dish with a 100W on UHF and bounce off the moon to the other side of the world.