Today i've played a bit with a small ferrite antenna for 630m.
It is 14 cm long and has 8 mm diameter.
Without any calculations i wound a winding of unknown number of turns
around the rod and quickly found C about 200 pF at resonance (475 kHz).
Then i added a few turns for a 50 Ohm output (measuring the voltage of
an induced signal at resonance. When applying 50 Ohm, the voltage has to
decrease to 50%) to the RX.
As expected the input signal is to low, it does not rise the noise of
the RX, so i'm missing about 20 dB. It can't be much more though because
i can receive IQ2MI/B clearly in QRSS-30 on 476.180 kHz with 25 dB SNR
in 122 mHz, see attachment.
The antenna is hanging in 6m AGL in a tree in my garden...
I'm playing with the idea of a rotary H-field RX antenna for MF, maybe
in combination with a stereo receiver and a E-field antenna. Oh and
maybe with a colour spectrogram as known from DF6NM. A lot of things to
PS: Yesterday, in a CW QSO with DK6SX/p on the loop he once completely
disappered into QSO which never happend before when receiving on a
omni-directional antenna. So i guess the colour changes in such a
spectrogram must be quite interesting and informative...