Instructables

two way radio wattage increase

is it possible to increase the transmitting power on these modern cheap little two way radios like cobra and motorola and midland. they say up 35 mile range but only if both people are standing on mountain peaks

I know this is an old thread but let clear up some misconceptions. The legal transmission limit for FRS is 500 milliwatts, or 1/2 watt. However in the GMRS range the limit increases to 5 watts. These two services have a 7 channel overlap. To increase the transception (transmission and reception) range of an FRS radio, one need only to improve the antenna. Most of these little handhelds have a simple coil of wire contained within a plastic shell and it has been my observation that these may or may not be properly tuned to the the exact frequencies they are designed for. At higher transmission power outputs this causes higher standing wave ratios and will cause damage to the final output transistors but at lower power will significantly cripple transception abilities. Often these little radios can be tuned to correct high standing wave ratios and increase range significantly. The most productive way however is to eliminate the little coil antenna and replace it with a 1/4 or 1/2 wave tuned whip antenna that is matched to the radio's design frequency. There are a few videos out there showing how this is done. For extreme increases in range it is a fairly easy project to eliminate the attached antenna altogether and replace it with a connector to which 50 ohm coax cable can be attached. Connecting this cable to a proper yagi or similar highly directional antenna matched to the frequency will provide ranges that far exceed even the manufacturer's ridiculous boasts.
lemonie4 years ago
Yes, but how do you feel about taking them apart and playing with solder & electronics? You'd need to build a more powerful transmitter in each.

L
not necessarily, you could also do it the ghetto way... but increasing input voltage


it would probably damage the amp circuit, and possibly change the transmitting frequency
Do you have an example of that method actually working?

L
no... it's just a theory
Putting more energy out would involve putting more in, but you'd have to be careful how it was done.

L
i was assuming that since the system has a resistance, more volts would equal more power output
Is it regulated, what current with the output amp take? We don't know on this one, but pumping up the output power would do it, whether upping the input voltage would is unknown.

L
If you up the input voltage into the radio, it will likely fry the radio since the radio circuitry is designed to only accept a certain amount of voltage. Adding more voltage to the input side of the radio probably won't have any effect to the amount of power actually transmitted.

The best way to increase your range would be to connect the antenna port to an amp, then transmit through the amp (which will increase the wattage to an antenna designed to handle whatever the output wattage is.) However, If the output power gets to be more than 4 watts or so, it is probably illegal (CB Radios use 4 Watts), but who's going to come looking for you if you are out in the woods? There aren't FCC agents hiding in the trees, waiting to catch you the minute you key up....

I would say that trying to get more range out of those little GMRS or FRS radios is probably more trouble than it's worth.

However, one option is to research the wavelength of the frequency you are using, then construct a full-wave antenna. (the radio is probably using a 1/8th wave or smaller size antenna) You would have to take the small antenna off of the radio, and solder in the full-wave antenna that you cut to the length of the wavelength. If you are lucky, the handheld antenna may just unscrew. Many antennas use a universal SMA jack that is really easy to get a replacement screw-on antenna for, and it makes it easy for making your own antennas because the parts are available at Radio Shack.

There are multiple sites for converting frequency to wavelength. Full wave antennas are better for transmitting and receiving than fractions thereof... They use the 1/2, 1/4, 1/8 wave antennas because they are much more practical for handheld use because they are small.

The legal output wattage is 1/2 watt, not 4. The FCC actually detects these things so you have a huge chance of getting caught. Don't do it! You would be committing a crime.
Dr.Bill4 years ago
You need to feed output power from the antenna connection inside the radio into a linear amp for 70cm frequency. Then attach the antenna to the output from the linear.
Google Ham Radio Outlet (HRO).
Dr.Bill Dr.Bill4 years ago
Of course you do know this will not be legal and the FCC will get you.
Those small radios are on frequencies designated for 1/2 Watt output.

Get your Amateur Radio License.
All will be revealed.
No more Morris Code requirement.
torgman Dr.Bill3 years ago
I believe it's "Morse code."
O-Budd-14 years ago
More power out means you need more power in, but it's probably illegal to do so.

OTOH, a better antenna is not illegal.

A four watt radio might actually get 3.7 W to the antenna, but if your atenna has a gain of just 3 Db over a dipole, you now effectively radiate 7.4 watts.

Every 3 Db is a doubling of radiated power. A 12 Db antenna will have a radiated output equivalent to 592 watts with 3.7 W supplied to it.
kricketone4 years ago
not advisable, low wattage close to the head is ok your talking about frying with that much wattage, close to your head...........
Lemonie has one way, the other would be to improve the directionality of the antenna. Technically, both approaches would be illegal - the radios are only designed to operate in a certain ERP.

Steve
Once upon a time, many many moons ago when I was just a curious young pup, I rigged a 100ft wire loop into the trees of my childhood home as a beeg antenna for a cheapo Sears walkie talkie. I took it from ~1/4" mile range to about 3 or 4 miles, as indicated by a guy several suburbs over who picked me up on the air.

Lettum come aftuh me, just lettum...bwahahahahhaha

(not sure if that would work for more modern radios though...I don't even know where you'd attach the wire to one of those cobra talkies' antenna.)