Long range challenge 2

 In the previous long range challenge in Plover Cove Reservoir main dam, the transmitter was using two parallel PN2222A as the final stage, that give 500mW output, this time, a new lot of BLT50 transistor was brought from another online store, it's rating is 1.5W, but can it really gives 1.5W? let's try to see the result.

with class B bias (= no bias) and power supply of 10V, 27MHz, the output power could be obtained is 31dBm. (28dBm showing in spectrum analyzer and counting -3 dB additional attenuator), this is a little bit more than 1W, but certainly less than the rated 1.5W as datasheet mentioned. May be the input power is not enough or output matching not good enough.

more than 1W output power, it's quite satisfying.

adjusted the instrument's stop frequency to ~250MHz, it shows quite many higher harmonics, well of cause, it's class B operation and not much output filtering.

Anyway, the transmitter is now upgraded from 500mW to 1W,  it's time for outdoor range test. The selected transmitter location is Ma Liu Shui Ferry Pier, and receiver location in Ma On Shan, they are about 800 meters apart. The previous attempt in this site was failed, because the receiver sensitivities was  just about -60dBm, obviously not enough. In this time the receiver sensitivities is increased to -90dBm. And the antenna of both side is 10cm longer than last attempt.

The bicycle trip

Transmitter is firstly placed near the pier, then I took the receiver and ride along the path shown, when riding along to the target receiving site, some signal (about 3 RSSI LEDs) could still be detected, even on the bridge, when riding closer and closer to the target receive site, the signal become very strong.

Mission accomplished. All 16 RSSI LEDs is on, showing full signal strength. The transmitter is on the opposite of the harbor. Which is more than 850 meters apart.

Sadly, I have to ride back to take back the transmitter.

Lesson learnt

Before deploying a radio, the output power and receiving sensitivities must be measured clearly using equipment.