Full wave? Yes, that’s obvious now I think about it. I’ll run down to the garage with my side cutter in a moment.
Back to the RFM69Pi, is it worth adding a ground wire to that? And if so, to where?
From what I understand the antenna ground is opposite the antenna connection on the RFM69 board, this is where I have other ground wires added in other nodes but they don’t have the problem of the ground contact being inside the RasPi case.
So, do I just use the other ground connection, two up from the antenna connection, so it can go down the outside of the RasPi case, OR do something like this -
and bring the ground wire across the RFM69 board and then down the outside of the RasPi case?
(and make the vertical drop the 1/4 wave length)
That’s the catch with the Hope RF modules. They don’t have a readily accesible RF ground - a very different animal than a DC ground. (especially at 433MHz and above)
You might find trimming your half wave elements to quarter wave gives you enough improvement you won’t have to add anything to the RFM69Pi.
If not, then experiment with routing the wire along various paths until you find one that gives acceptable results
Interesting that the user with the nRF24L01 module was able to make his dipole work. At 2.4GHz, getting things “right” is generally quite a bit more difficult than at 433MHz. (Things that have little or no effect at 433 MHz, often behave very differently at 2.4GHz)
Ok, so in my haste to cut down the antennas I dropped the garage node and snapped a power lead off, so I brought it inside to resolder it. As it happens I also moved my RaspPi back to my study last night (to swap the SD card for a larger/faster one). Having repaired the garage node, I checked EmonCMS to make sure it was transmitting OK, before I took it back out and noticed something odd. Even though there is only around 1 metre of fresh air between the node and the RFM69Pi, the rssi signal is bouncing around between -40 and -50. Surely it ought to be better than that?
Half wave dipole on the node, 1/4 wave monopole on the RFM69Pi ?
Moving it to the other side of the room, about 4 metres but still clear LOS, it gets to -56.
At this signal strength it’s no wonder it can’t hear it from the garage…