Problem with wireless Transmitter-reciever

I am working on Tx Rx based on HT640 and HT648 on 434Mhz with ASK Module. I am in search of a good compatible antenna for the same because I always face problem of range while operaing it. Please suggest me something! Thank you...

I've used a simple 6" wire as antenna. Try with that, it will be quick too.
What range you are looking at to achieve?

-kjs

I had used simply a 5"-6" wire as antenna, and the range was around 80-100 feet.

Thanks for your replies. But is there any specification for the wire to be used?

No need of any specific wire, I had just used a simple thin wire and that's all.

Correct, use any of the wire but keep the length in multiples of 6". Also, the module you are using should allow you to vary the field strength.

We used radio antenna, which are very cheap and we can adjust the height of the antenna to our wish..... I got a very good and considerable length coverage with that too.......

Yagi antennas designed for the 70cm amateur band will give you more range than any variation of a vertical/whip.