Have someone suggestions to try or good links to read? Especially for:
- when a ferrite or iron powder rod/bar goes in saturation?
- optimal rod dimensions
- optimal coil design (I suggest single layer, resonating with good Q
capacitor, about 3 to 10 turns)
So there is a resonant circuit at the transmitter and not just a coil?
I tested it as resonating circuit using the original time-code receiver
antenna AND a second time without the capacitor.
Maybe I got a little more power in the air with the resonating circuit, but
it was not very distingiuable.
With such low number of turns (and hence low inductance), the
capacitor would have to be huge to resonate it at 77.5 kHz. Where do
you get high Q capacitors with such capacitances ?
I don't know the exact manufacturer of the time-code receiver ferrite
antenna but I comparable model reads:
L=900uH
bandwidth=700Hz
n=94
see original data
http://www.hkw-elektronik.de/pdfengl...00-77,5-DE.pdf
It is not the same antenna but very similar.
The original foil-capacitor is 682 labeled. I don't measured it but I think
it should be 6800pF reading.
For my second experiment I used no capacitor and turns=10.
If I would find a PSPICE model for an ferrite antenna ...
The resonant circuit impedance levels are quite low in this
configuration (small L/large C), how do you effectively couple power
from the transmitter to this low impedance level at the resonant
circuit ?
Hm. I thought he just trying different turns value to achieve this. The
coil is the impedance transformer for the ferrite rod (=antenna). I'm wrong
here?
The skin depth at this frequency is about 0.25 mm, so any wire thicker
than 0.5 mm will not utilise the full copper wire, so some kind of
Litz wire with separately insulated strands could be used to keep the
coil resistance low.
The original coil is thinner than 0.3mm. If I compare it to my 0.3mm wire
maybe it is 0.18mm. The second experiment with the 10 turns coil is 0.3mm
enamelled copper wire.
I will give Litz wire a try if the system as such works...
The inductance of some ferrites varies if there is some DC field
present. This inductance change could detune the resonant circuit and
drop the radiated power. Are you sure that the transmitter coil is not
carrying any DC components or some even harmonic distortion, which
would cause an unbalanced magnetic field in the ferrite rod ?
Good question. I series blocked DC with a WIMA MKS4 1.0uF 100VDC
high-quality capacitor. As measured the "big" capacitor is outside the
bandwidth of the antenna.
I don't think there is any DC component left. And yes, there is no magnet on
my desk laying around :-)
Is there any internal rectifiation phanomen in the ferrite possible?
- LNA design for such a low frequency?
The band noise is the dominant (compared to "white" amplifier) noise
when listening to the band with your transmitter switched off, the
receiver noise performance should be adequate.
How much band noise should I expect?
- Henry