ISL Operating Range at 146 MHz

We compare reception of repeated commands by the A3024A and the A3030A. We fasten an example of each to a piece of cardboard.



Figure: Two ISLs Strapped to Cardboard for Command Reception Test.

The A3024A simply turns on its lamp when it detects radio-frequency (RF) power above a threshold. We set the threshold as low as we can. The A3030A turns the incoming RF signal into a sequence of byte instructions with a checksum at the end. When we send repeated commands to flash the A3030A lamp, the A3024A lamp illuminates while the command is being transmitted, and the A3030A lamp illuminates afterwards, provided the command has been received without corruption.

We use our 146 MHz Command Transmitter (A3029A) with boost power to produce the RF commands. We measure maximum range of reception, for a favorable orientation, and maximum range for reception in 95% of orientations. We also test reception with the two devices in water, as shown below.



Figure: Two ISLs In Water for Command Reception Test.

We measure maximum range for reception in water. Now we add 5 g of salt to the 500 ml of water and stir until dissolved. We measure maximum range again. We present our observations below.

Test	A3030A No1.2	A3024A No7
Robust Reception Range on Cardboard	70 cm	100 cm
Maximum Range on Cardboard	250 cm	600 cm
Maximum Range Held By Lamp and Dangling	300 cm	900 cm
Maximum Range in Water	70 cm	450 cm
Maximum Range in Saltwater	70 cm	450 cm

Table: Comparison of Reception for Encapsulated A3024A and Encapsulated A3030A.

It occurs to us that encapsulation or an exhausted battery might affect No1.2's reception, so we try an un-encapsulated A3030B with a fully-charged battery and measure maximum range in air. We get 250 cm, the same as for No1.2. We walk around with the lamp held in our fingers, and the device dangling below, and repeat our measurement of maximum range.

The A3030A must monitor and interpret the exact timing and content of the digital RF signal it receives on its two-turn loop antenna. Compared to the A3024A, which simply turns on its light in response to any received RF power, the A3030A has substantially shorter operating range (70% far in air for robust reception). In air, the A3030A's maximum operating range is one third that of the A3024A, but in water it is only one sixth that of the A3024A. In 1% saltwater, operating range is unchanged.

We place the A3030A in a jar of fresh water. It rests on the floor. We move it around 50 cm from the antenna and obtain robust reception. But there are orientations that are hard for us to obtain with the transmitter loose in the water, so we suspect that robust reception in all orientations would be closer to 30 cm. At ION, we observe robust operating range for an implanted device is only 20 cm.