Have just fired up Hooter's HopeRF HM-TR FSK transceiver pair (working into a couple of 08Ms), which fit nicely on the usual small breadboard OK. The RS-232 types supplied have a Max232 on board already- as shown in the pix below. The config. setup (which runs under even W98 on an old serial laptop) is very nifty,& my usual PICAXE header pin programming lead did serial pins 2,3,& 5 double duty OK when links were made. Changes (such as the 9600-2400bps) stored away readily on the Hope units. Two SMD LEDs very usefully show activity - green for signals being received, red tx etc. Anticipatory hand rubbing was in order!
However the transmitter power setting was immediately annoying, as the maximum seems only 0dBm (1 milliWatt), with changes (such as -10 dBm =100 µW) only for LOWER powers. Every 3 dB increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. For a 3 dB decrease, the power is reduced by about one half, making -3 dBm equal to about 0.5 milliwatt. ARGH- this is quite pathetic given the ISM band allows 25mW legally, & most ASK "garage door openers " are ~10 dBm (~10mW). Predictably hence 0dBm made for pretty trivial ranges, with ~100m LOS,when connected to the supplied rubber ducky, being all I could manage to hear even on a sensitive scanner.
Additionally frequency settings (such as 433.92MHz) do NOT equate to the correct output noted on the scanner, which in this case was 434.105 MHz. I suspect one of the units is defective as well (Hooter- any insights?),since when programmed identically it behaves totally differently to the other.
I'll readily accept my late night approach may have fast tracked setup needs (running on 3 x AA instead of a regulated 5V etc, failing to await a buffer fill out etc), & since instructions are minimal will have to patiently explore everything, & maybe email HopeRF themselves. However, in comparison to the likes of traditional ASK Jaycar 433 offerings, these HopeRF HM-TRs performed poorly. Has anyone else got these units handy for comparisons?
Initial feelings hence are that they may well be "all show & no go" for PICAXE work.