Ferrite rods are commonly used as RX antennas on MW and LW. They are compact and efficient for their intended purpose. Their use as TX antennas is almost non-existent.
As long as the ferrite is suitable for the frequency and as long as the ferrite is not in saturation, they may be used on TX. This implies very low power, but we know on WSPR and possibly FT8, long distances may be spanned with very low power indeed. Certainly great ranges have been covered with milliwatts and microwatts.
Some years ago, I did some TX tests with ferrite rods and the results surprised me.
In absolute terms, I have little idea about their loss compared with, say, a dipole. At 630m and 160m, antenna efficiencies are often -30dBd or worse, so they could be far better than we might expect. They certainly are small! Some people have bundled several rods together. I have not tried this.
This is yet another area in which radio amateurs can carry out useful research. Be careful that the ferrite rod alone is doing the work and you are not coupling into a bigger antenna nearby.
In my view ferrite rods "compress space" within the rod. As such, they could be used as magnetic or loading in E-field antennas.Remeber to keep power very low.
See https://sites.google.com/view/g3xbm4/home/antennas/ferrite-rod-tx-antennas .
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