RF Modem + 250mW Amplifier


[Trax] sent in his writeup on this RF modem with built in 250mW amplifier. The original power of the RF transceiver was around 10mW, his final results after testing were nearly 250mW. He was able to to easily transmit data over 1000 meters using his test setup. He states that he was actually able to achieve this without an antenna on the receiving side. That’s pretty impressive performance. It’s also worth noting that he soldered all of the components in place using a home clothing iron and some soldering paste. That must have been fairly tedious.

37 thoughts on “RF Modem + 250mW Amplifier

  1. The article is posted on a Bosnia-Herzegovina domain web site, so “illegal” as we Americans or Europeans think of it doesn’t apply.

    Unless you operate one here in America, that is. Then the FCC can rain all over your parade.

  2. luigi: I think you are missing something. These are all surface mount parts, and soldering this by hand would actually be harder.

    With solder paste the components will tend to self center. Also if you are experienced enough with dispensing, you might not even have to do rework/cleanup.

  3. I know of some people that might not agree with the logic behind sticking a power amp on. A more elegant solution, and often with better results, is to use a LNA and rather boost the received signal instead, increasing sensitivity.

  4. leon first you say it would increase sensitivity, then that it wouldnt. Make up your mind :)
    Anyway its moot as he is pumping out on GSM band and has to fight with Cell towers.

  5. sorry, that’s with regards to the “GSM band with lots of cellular noise” will probably only effect SNR. (this could turn ugly) you’d also have to look at what modulation scheme is being used by each (chipcon radio and GSM) if you are looking at interference.

  6. “The article is posted on a Bosnia-Herzegovina domain web site, so “illegal” as we Americans or Europeans think of it doesn’t apply.”


    “Bosnia and Herzegovina is a country on the Balkan peninsula of South Eastern Europe with an area of 51,129 square kilometres (19,741 sq mi). “

  7. Kind of like my 10W FM transmitter amp. I use it to block out the RAP stations when I am on a construction site.

    Some of those insulation guys or drywallers listen to some really crappy music, great to go to the car, flip on and kill that station with a nice blank station.

    I typically send nothing, but I can transmit my Sirius radio as well… works good on larger sites when I am programming a Lighting control panel or Honeywell Access Panel.

  8. I’m fairly certain that this does not interfere with cellphone bands, unless you really eff up the transmitter.

    Anyway, 900Mhz is an ISM band and not nearly as illegal to mess around with as, say, jamming other stations on FM *ahem*. In fact, I know for a fact that there are commercially available 1W 900Mhz transmitters on the market–as another reader mentioned, if the wireless system is frequency hopping, this isn’t even close to the maximum power output allowed (in fact, you’re allowed 4W maximum EIRP, so 1W with a 6dBi antenna–the one he used was only 3dBi, I think).

    Of course, I don’t know if this applies for Europe, and I think any wireless DIY project is a bit mucky since you’d usually have to get your circuit FCC approved first and whatnot. I haven’t looked at it yet, but I’m fairly certain that implementation he uses does not employ frequency hopping (though the CC1100 is definitely capable of it)

  9. Very nice work under the circumstances!

    If they get that kind of performance without an antenna then imagine what using a pair of properly tuned radiators would do!

    -Based on this performance you could probably go hellishly far with a set of properly aimed directional antennas.

    combining radio with data stuff is probably my favorite combination of disciplines.

    kudos dude

  10. i’m pretty skeptical that he’s actually getting 1km on 250mW, without an antenna, especially with a shit-ton of 900mhz noise. maybe a few valid packets of data, but theres no way it could be a stable stream.

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