Anyone interested in a copy of this, as managed to recover "something" from old notes suggesting that to send a signal back in time is a lot simpler than first thought.
Essentially the method is to set up the SDR receiver and datalogger beforehand, continuously record the signal and aim the transmitter at a region within the thunderstorm that is likely to produce positron clouds and thus has a chance for a CTC to form for 1-5 seconds as the positrons decay.
It only really needs a couple of Watts RF if done right, even a simple dish with 1/4 wave antenna should work but for safety it is better to ensure that any signal generators send short bursts of data only with a very simple pattern such as short number sequences which can show up on the SDR as a frequency comb distribution.
If someone else stumbles across it they will get gibberish.
I am not precisely sure but some RF anomalies such as long duration repeats may be linked to this effect.
Intriguingly I think this happened once by accident a few months ago, got some sequences suggesting various events that did in fact occur (eg Shape of Water winning Best Picture).