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.


  1. wacco says:

    Fantastic trick.

    Also very illegal in (afaik most of) europe, at least at the maximum power setting.

  2. free4all says:

    VERY illegal in USA with in 250 miles of any military facilaty

  3. free4all says:

    BUT i want one!!!

  4. t says:

    it sure is illegal unless you use frequency hopping with a allowed hop-rate. then you can use up to 1W of power. you can find these regulations online.

  5. jaded says:

    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.

  6. andrew says:

    you can use it if you are a licensed ham and you used it within the correct frequencies. so it would actually be very useful for some people :)

  7. sly says:

    yeah, some folks really like to ham it up

  8. anonymous says:

    “ham it up”

    I see what you did there. Radio humor FTW.

  9. Anonymous says:

    “ham it up”

    I see what you did there. (RF humor FTW.)

  10. luigi517 says:

    props but seriously dude, should probably get a soldering iron costs 5 bucks and would make your life alot easier

  11. jproach says:

    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.

  12. The Moogle says:

    so go screw an elephant free4all

    omg im so drunk lol

  13. Obama says:

    I am Barack Obama and I approve of moogle’s message

  14. the moogle says:

    Thanks Barack, lets go screw an elephant

  15. M4CGYV3R says:

    Someone give me a piece of chewing gum, a paperclip, and a drinking straw… I want to try to make one of these.

  16. Harry says:

    Illegal in most countries: YES
    Do I want one: DEFINITELY YES

  17. ineedhelpbad says:

    Albert everyone knows it RDA. Now wheres that elephant.

  18. john kerry says:

    i won three purple hearts. i approve this message.

  19. leon says:

    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.

  20. rasz says:

    hard to increase sensitivity when you operate on GSM band with lots of cellular noise

  21. leon says:

    wouldn’t effect sensitivity, more likely to effect signal to noise ratio. you’d still get better results with LNA in comparison to HPA.

  22. anon says:

    harry I think you missed out something:

    illegal in most countries: yes
    => do I want one: definitely yes

  23. rasz says:

    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.

  24. leon says:

    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.

  25. Teebo says:

    Hey everybody thanks for telling us that it’s illegal, Buzz Killington.

  26. Jan says:

    leon: you can’t improve snr by simple amplification. the noise level will be amplified by the same amount.

  27. leon says:

    jan: not sure i implied anywhere that snr improves with amplification.

  28. Steve says:

    “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). “

  29. cmholm says:

    He wasn’t claiming bosnia-herzegovina wasn’t part of Europe. He’s suggesting that the regulatory environment there is a bit loose.

  30. fartface says:

    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.

  31. threepointone says:

    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)

  32. strider_mt2k says:

    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

  33. samurai1200 says:

    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.

  34. Rob says:

    I’m really getting into RF electronics/communications. Are there any good RF websites/forums out there?

  35. Oleg Mazurov says:

    I used Xbee PROs for links over a 1000m( with antenna ). They are cheap and legal. The power is 60mw, current consumption 300ma.

  36. me2 says:

    Wave Magnum – High Power USB Wireless Adapter. Huge 1/2 Watt output. FTW


  37. these are really great to have..it is great to see you..

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