Breakthrough of the year 2014 - Long range challenge

Breakthrough of the year! Plover Cove Reservoir main dam long range challenge completed!

It has been a long time goal for me to making a wireless range that could cover the main dam, using 27MHz band and just a monopole antenna. Previous attempts was not successful because the power of transmitter was not enough and sensitivity of receiver is also insufficient. 

It's not easy to get to a good test environment in urban area because the buildings and terrain blocked the signal. The only testing site having straight open channel is the Plover Cove Reservoir main dam.

The simplest form of communication transmitter is to merely feed a carrier to the antenna, no modulation, the key point is big power. Previous attempts was an crystal oscillator stage and one stage of power amplification. In this attempts, one more stage of power amplification is added, coupled by 4:1 step down transformer.

The transmitter with 650mm monopole antenna on ice-cream stick.

27.76 dBm output power, which is more than 500mW

(Note that CRT of this analyzer gone crazy just after boot up for a while)

The transmitter was firstly placed on the beginning of the dam and receiver walks towards the end of the dam. 

The receiver showing the carrier is still detected, at the end of the dam. The sensitivity of this receiver is measured as -90dBm. I guess if need better sensitivity, a double conversion architecture is required.

The receiver signal strength indicator LEDs gradually show lower and lower signal strength until the end, 3 of the total 16 LED still remain shining, what a relief.