Looking to buy ready made RF transmitter (40 to 200) khz

hello ,

i am looking to buy Radio frequency transmitter ( 40 to 200 ) khz , coverage area for that transmitter 200 m radius,

so please if some one know how to build it , please let me know ,

br,
wael :thumbsup:

More information is needed.
What is it for?
what modulation type (if any)?
what antenna is available?
power requirements?
power supply available?

Brian.

betwixt said:

More information is needed.
What is it for?
what modulation type (if any)?
what antenna is available?
power requirements?
power supply available?

Brian.

Click to expand...

Hello Sir,

i am looking to buy a simple radio transmitter (40 khz to 140khz ) which will need transmitting antenna TX antenna to fit / comply with same frequency band ( 40 khz to 140 khz ) , thistransmitter has to provide radio coverage ( with out modulation only RF signal ) over 200 m distance ,

The mentioned Transmitter will be used for Geological research ,It will support one ready made LF receiver developed by Germany company called EMFAD ,

Please note that i already have the receiver it is called EMFAD ug 12/4 ( passive receiver for low frequency band 40 TO 140 KHZ) ,

This model of EMFAD ug 12/4 , can’t be used worldwide , Because the EMFAD - UG 12 / 4 uses signals from the VLF - radio stations rather than transmitting ,but in many area over the world the VLF signal very week due to far distance ,

so we face issue during the scan in the measuring areas most of time no signal or only weakly incident transmitters (VLF stations )can be detected by the receiver,

so i think to build own transmitter to generate frequencies between 40 to 140 khz , to allow the EMFAD ug 12/4 unit get the signal and send it to the ground to detect the targets

betwixt said:

More information is needed.
What is it for?
what modulation type (if any)?
what antenna is available?
power requirements?
power supply available?

Brian.

Click to expand...

Transmitter unit required features / specification:

1-Transmitter frequency:
Frequency can be selected from 40 khz to 140 khz.
2-Input power:
12v- DC or 18 v (2* 9V) Dc, both options should be rechargeable battery
3-Output Radio frequency power:
10 to 30 watts (to provide RF coverage range from 200 m to 300 m)
4-Transmitter Antenna:
Loop antenna or Air core antenna or Telescope antenna , any model can transmit the required band (40 to 140) khz.
condition : the transmite should be direct to the air like radio station , not by rod to the ground
Antenna Size: small will be better
5- Weight for transmitter:
As much as small will be better

I presume the measurement method relies on an (almost) homogenous VLF far field. It's effectively impossible to generate a similar field with small antennas in the vicinity. Something that might work could be a loop around the area under investigation.

Did you already ask the manufacturer for suggestions about using local VLF transmitters?

FvM said:

I presume the measurement method relies on an (almost) homogenous VLF far field. It's effectively impossible to generate a similar field with small antennas in the vicinity. Something that might work could be a loop around the area under investigation.

Did you already ask the manufacturer for suggestions about using local VLF transmitters?

Click to expand...

yes i did, they build transmitter can transmit only 6 frequency in that frequency band ,and they used wire loop antenna 40 m length , and the lay it on the ground ,

but all the feedback from users ( all of them my friend ) was negative , the transmitter what the manufacture made it is send the signal through the ground !!! by laying the wire antenna above the ground , it is seem the transmitter generate harmonic signal , not RF signal , so the quality of the scan photos were very bad ,

the idea from the RF Transmitter that will act as small VLF station , signal will be available in the air not through the ground , once we have strong signal strength in the air then w will have best performance ,

br,
wael

signal will be available in the air not through the ground , once we have strong signal strength in the air then w will have best performance

Click to expand...

I fear, this analysis can't be substantiated by electromagnetic theory. I rather guess that the loop is still to small, I would suggest a margin of 10 or 20 meters around the area under investigation.

I'm not sure if and how the system performance depends on the VLF field orientation. A horizontal loop can only generate a vertical magnetic field
component, other orientations are hard to achieve without building huge scaffolds. Also the detected object is always in the near field which may also affect the system operation.

Transmitter signal quality might be another problem. But without an exact description we can't know what the manufacturers transmitter option is actually doing.

Making a CW VLF power amplifier is not such a tough work, and doesn't require great hardware design knowledge. And the components are really cheap.
Here you can find how to build a cheap VLF (136kHz) power amplifier. In front of it you can place a simple crystal oscillator followed by dividers to get the desired frequency, and finally you get a complete CW VLF transmitter.

https://www.g0mrf.com/classd.htm