Hi John,
Thanks for your response and sorry about the late reply. Just to clarify a few points...
Regarding the helical vs single wire (1/4 wave monopole) antenna, all that I’ve read suggests you are right but I simply can’t seem to trim the Gateway and Node antennas to a length that outperforms the helical. I’ve had a few goes now – and although the technique is not “scientific” I am measuring RSSI with every trim (of approximately 3mm) and the best I get still underperforms compared to the helical.
To be clear, I’m using a right angle SMA connector with a crimp cable side. I remove the crimp sheath (leaving a hole through to the centre pin) and heat / gun solder paste to connect to the centre pin. I am VERY careful to insulate against the ground. The antenna wire is the copper core of a 75ohm coax cable. You mentioned that I should try 50 ohm, and I get it that the impedance of the radio is 50 ohm but we are just talking a piece of wire here – does the diameter of the wire affect the impedance? Everything I’ve read suggests not, the dielectric compound surrounding the inner core cable – and the shield composition has the most effect, although diameter of the inner core does affect impedance, it should be offset by trimming the wire. All connectors (the SMA, uFL nas pigtail are 50 ohm rated – as is the input to the RFM69HW.
Regarding the grounding – I’m pretty confident this is extremely low resistance. The uFL pads are within a mm of the radio pads and all are contact make – with over solder. Probably as good as Felix’s, Moteino – although his construction techniques would no doubt be better than mine.
Regarding the breadboard assembly, I rigged a RFM69HW to some veroboard and soldered an antenna exactly the same as the ones provided by Felix with the Moteino directly into the Antenna pad trough-hole on the RFM69HW. The SPI wires to the ATMEGA chip were jumpers – the regulator etc... were rigged pretty much in the same way.
One thing I note is that I’m running my config at 1200Bps and the specs for the radio suggest I can get comms at -120 db. With the breadboard assembly, I note I’m getting RSI around -110 at 150 metres before I lose communications (I’ve detailed in this post...
https://lowpowerlab.com/forum/low-power-techniques/low-power-listenmode-with-lower-baud-rates/).
With my current fabricated PCB I never get a connection with anything above 100 dB in ListenMode – and the range is around 80 metres at best.