RF modem + 250mW amplifier

posted Apr 2nd 2009 1:34pm by Caleb Kraft
filed under: classic hacks, wireless hacks

[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.

Comments [37]

tagged: rf modem, transceiver, wireless

Reader Comments

Fantastic trick.

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

Posted at 2:00 pm on Apr 2nd, 2009 by wacco

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

Posted at 2:04 pm on Apr 2nd, 2009 by free4all

BUT i want one!!!

Posted at 2:05 pm on Apr 2nd, 2009 by free4all

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.

Posted at 2:13 pm on Apr 2nd, 2009 by t

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.

Posted at 2:33 pm on Apr 2nd, 2009 by jaded

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 :)

Posted at 2:37 pm on Apr 2nd, 2009 by andrew

yeah, some folks really like to ham it up

Posted at 5:14 pm on Apr 2nd, 2009 by sly

“ham it up”

I see what you did there. Radio humor FTW.

Posted at 6:08 pm on Apr 2nd, 2009 by anonymous

“ham it up”

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

Posted at 6:10 pm on Apr 2nd, 2009 by Anonymous

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

Posted at 6:18 pm on Apr 2nd, 2009 by luigi517

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.

Posted at 7:53 pm on Apr 2nd, 2009 by jproach

so go screw an elephant free4all

omg im so drunk lol

Posted at 10:18 pm on Apr 2nd, 2009 by The Moogle

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

Posted at 10:28 pm on Apr 2nd, 2009 by Obama

Thanks Barack, lets go screw an elephant

Posted at 10:29 pm on Apr 2nd, 2009 by the moogle

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

Posted at 10:40 pm on Apr 2nd, 2009 by M4CGYV3R

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

Posted at 1:51 am on Apr 3rd, 2009 by Harry

Albert everyone knows it RDA. Now wheres that elephant.

Posted at 1:57 am on Apr 3rd, 2009 by ineedhelpbad

i won three purple hearts. i approve this message.

Posted at 2:43 am on Apr 3rd, 2009 by john kerry

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.

Posted at 2:49 am on Apr 3rd, 2009 by leon

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

Posted at 4:30 am on Apr 3rd, 2009 by rasz

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

Posted at 5:39 am on Apr 3rd, 2009 by leon

harry I think you missed out something:

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

Posted at 5:59 am on Apr 3rd, 2009 by anon

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.

Posted at 6:28 am on Apr 3rd, 2009 by rasz

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.

Posted at 6:45 am on Apr 3rd, 2009 by leon

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

Posted at 6:50 am on Apr 3rd, 2009 by Teebo

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

Posted at 7:29 am on Apr 3rd, 2009 by Jan

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

Posted at 7:40 am on Apr 3rd, 2009 by leon

“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). “

Posted at 9:33 am on Apr 3rd, 2009 by Steve

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

Posted at 10:48 am on Apr 3rd, 2009 by cmholm

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.

Posted at 11:13 am on Apr 3rd, 2009 by fartface

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)

Posted at 2:32 pm on Apr 3rd, 2009 by threepointone

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

Posted at 4:30 am on Apr 4th, 2009 by strider_mt2k

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.

Posted at 9:28 pm on Apr 6th, 2009 by samurai1200

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

Posted at 4:31 am on Apr 7th, 2009 by Rob

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

Posted at 9:53 am on Apr 16th, 2009 by Oleg Mazurov

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

http://www.radiolabs.com/products/wireless/wave-magnum.php

Posted at 3:36 pm on Apr 17th, 2009 by me2

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

Posted at 2:23 am on Sep 17th, 2009 by Sweton T Fleming

RF modem + 250mW amplifier

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