Reducing RF power of video transmitter

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Discussion Overview

The discussion centers on reducing the RF power output of a 2.4 GHz video transmitter to limit its range, with a focus on materials and methods to achieve this goal. Participants explore various approaches, including physical modifications to the transmitter and the use of shielding materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests creating an enclosure from conductive materials like copper, aluminum, or graphite to reduce RF output.
  • Another proposes cutting the antenna to less than an inch or removing it entirely to limit transmission range.
  • Some participants discuss the effectiveness of thin layers of aluminum foil versus solid aluminum for shielding.
  • A participant mentions the possibility of using an RF attenuator, specifically recommending a 30 dB attenuator, while cautioning about potential leakage from the transmitter housing.
  • Concerns are raised about the transmitter's power supply leads or the circuit board itself potentially radiating signals, suggesting the use of anti-static bags for testing.
  • There is a discussion about the legal implications of using the transmitter for surveillance purposes, with one participant expressing discomfort about the intended use.
  • Another participant inquires about the feasibility of signal scrambling to protect the video signal from casual observers, emphasizing size constraints for any additional circuitry.

Areas of Agreement / Disagreement

Participants express a variety of opinions on methods to reduce RF power, with no consensus on the best approach. Some ideas are challenged or refined, but the discussion remains unresolved regarding the most effective solution.

Contextual Notes

Participants highlight limitations related to the specific frequency of the RF attenuators and the potential for signal leakage from various components of the transmitter. There is also uncertainty about the effectiveness of different shielding materials and configurations.

Who May Find This Useful

This discussion may be of interest to individuals working on RF transmission projects, particularly those involving video transmitters, as well as those concerned with signal security and legal implications of surveillance technology.

  • #31
sophiecentaur said:
It does strike me that the best solution to your problem might be to use a very low power RF signal source in the first place. For instance, you could do away with the final RF amplification stage of the unit. It's a waste to generate the power then to dissipate it inside the box!

I second that. Your batteries would last longer as well. If there is an external amp in the circuit, typically there is a resistor that is tied to the output of amp. This is a current limiter that sets the output power. It should have a value from 1 to 300ish ohms. Replace that one with one that is slightly higher and see if the transmission distance drops.

As for ferrites
http://mouser.com/search/ProductDetail.aspx?qs=uSeJpk%2f8In1VmERn9ukNjA%3d%3d

those are rated for 2.4 GHz operation
Murata has information about their ferrites here
http://www2.units.it/carrato/didatt/el_appl_2/doc/filters/murata_sf.pdf

You can read about which ones are suited for use @ 2.4GHz
 
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  • #32
fizz_it said:
This is a current limiter that sets the output power. It should have a value from 1 to 300ish ohms. Replace that one with one that is slightly higher and see if the transmission distance drops.

I'll look into it and see if I can identify it. The transmitter I'm using is a tiny little circuit board 1/2" x 1/2" and covered with some heat shrink plastic that looks to be epoxied at the ends, so its going to be a pain to even uncover the board. Thanks for the tip on those ferrites...ordered some.

Lars
 
  • #33
Since it appears that you are looking to make this into a business, let me give some advice. Get the expertise to get the job done right. Contract out. You will save time(and money) for yourself, and come out with a device that performs better.
 

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