Radio booster amplifier

[concrete_hed]

Im thinking about buying a pair of cheap walkie talkies, they have a range of 3km line of sight, they transmit at 0.5 watt and have 40 UHF chanels. For what i want to use them for requires them to transmit 5km over some small hills and tree's.

 

I was looking in some old electronics books i had and i saw there was a radio booster amplifier circuit. This uses a 9v battery, a NPN transistor and a few other bits to amplifiy radio frequencies (from about 80 - 800mhz) and send them to the receiver.

 

Without buying more expensive transievers or CB radio's, what can i do to increase the range? How much power would i need to reach 5km? what would be more effective, using a radio booster amplifier or extending the aerial or both? do most radio's have radio booster amplifiers built into their circuits?

[YT2095]

sounds like you`re talking about PMR446 style radios, they`re roughly around the 70cms band.

 

they are licence exempt > 500mW, above that you have to pay yearly.

boosting the RF out doesn`t really gain you much in the way of distance though sadly unless you get into the 5w or more range.

boosting Reception is usualay the answer the best way with these thing, and a pre-amp would work quite nicely. also Antenna positioning is a great help too.

they usualy have a 1/4 wave spring coil antenna built in, if you could wire in a breakout conector to suitable coax (BNC connectors are typical for this) and make a SWR`d in antenna to match, that would help considerably.

also, running the thing off a main adaptor instead of batteries helps too, you can even go a little Over-Voltage with it also (but that voids it`s legality as some will increase power by doing this!).

 

just a few ideas for you

[concrete_hed]

A pre-amp u say ayy. Where would this pre-amp go? on the microphone? on the antena? how does it work exactly?

 

I know its probly not legal but how would i get 5watts transmitting power out of a walkie talkie? would i need something like i mentioned earlier that is connected to the antenna but instead of boosting the receiving waves, it boosts the transmitted waves?

[YT2095]

the pre-amp goes inline with your antenna coax usialy inductor coupled, a Linear amp (burner) does the same also, but as that detects that you key up and RF hits the board a relay switches over and re-routes your 500mw to an RF amp and then shoves that out the other end at whatever power your output transistor wiil allow at the other end to your ant.

when you drop the key the relay switches off and you have a straight pass from ant to unit for receive.

 

you don`t want to boost your mic in anyway as you`ll be over deviating/modulating, and more than likely causing bleedover to adjacent chans ( a great way to get complaints and yer equip taken off you!).

[concrete_hed]

so do u know any circuits schemats or where i can get any circuit schemats for this kind of pre-amp your talking about?

[YT2095]

before you can get into specifics such as this, you must idealy find what band/freq these radios operate at, the principal is the same for all, but specifics vary widely.

[concrete_hed]

Ok, i am dealing with UHF around 470 - 477 mhz. The transmitters are 0.5watt and i would like to get that up to about 1 - 2 watt. What is the easiest way possible to do this. Im thinking something along the lines of a repeater (recieves a signal from a selected band and them amplifies it), is it possible to make one using a fixed crystal clock oscillator?