Ferrite rod transmitting antennas?
OK, I only tried this with WSPR and with low power, but at my old QTH I had a good deal of success using a small ferrite rod as a TX antenna on some HF bands. As long as the ferrite is not in saturation there is no good reason why it should not work. Most problems will occur if the antenna is driven with too much power.
See the link for more details. I have no idea about this ferrite rod’s properties but I think it was a fairly standard piece of ferrite rod and nothing too special at all.
Since being in hospital for 3.5 months and moving QTH I have not been able to find the ferrite rod to repeat the tests. My wife moved most of my stuff and it is probably deep in a box somewhere! At some point I guess it will just turn up.
See https://sites.google.com/site/g3xbmqrp3/antennas/ferrite_tx .