I've got these 3 modules from Radiometrix. Look how nicely packed these came!
- HX1: VHF transmitter, hard-tuned to 144.8 MHz, outputs 300mW. Consumes 120mA at full RF.
- NRX1: VHF receiver, hard-tuned to 144.8 MHz
- UHX1: VHF transceiver, can operate on any frequency in a 2 MHz range, outputs 500mW (adjustable).
I've tried the HX1. It outputs 200mW according to my power meter. The 100mW loss might be due to the dirty connection I made from the breadboard to the SO-239 connector, bad shielding or the meter itself but I still haven't figured it out completely.
I've got the HX1 partly inspired by VE6SBS Barry's page. He successfully tracked a balloon using an HX1 radio from 600 km away. Not bad for 300 mw! I have been able to reach digipeaters in the ~35 Km range with ~50% success rate using the HX1 and a DIY 6 elements yagi antenna. With my trash-dug omni antenna, though, the success rate goes down to ~0.01% (success rate with the SRB MX146 @500mW and the omni was ~4%) , even though I have direct line of sight with the remote digipeater. I fear losing the ballon after it goes a few kilometers high, but apparently altitude has a huge impact in VHF propagation, and Barry's experience is a good proof of it.
The other issue Barry was worried about is the high frequency drift this device experiences with temperature. I think there is little to do here except taking care of good thermal insulation. I'm actually thinking of using the HX1 as a heat sink for the voltage regulator...