designing LF loading coil - self resonant frequency

Thread Starter

tmarco

Joined May 31, 2018
22
Hi guys,
does anybody know whether there's a rule-of-thumb or something along those lines to determine how far the self-resonant frequency of a coil has to be from it's working frequency? This would be within the context of designing loading coils for LF amateur radio, specifically for the 137 kHz band. For example, if the SRF of the coil was calculated to lie somewhere around 160-170 kHz, would that be too near? Cheers
 

Ylli

Joined Nov 13, 2015
1,083
Your OK, but just remember that as you get near the SRF, the reactance of the inductor will be greater than you would expect from the inductance value.
 

Thread Starter

tmarco

Joined May 31, 2018
22
Hi Ylli, could you maybe be more specific? I understand that commonly the reactance vs frequency is plotted with a VNA , from which
it is evident where the increase in reactance becomes unacceptable, so that gives directly the useful frequency range for the coil. However is there any way to predict this without constructing the coil first? Or maybe an approximation, like having the SRF at least 5% or 10% above the frequency of interest?
 

Ylli

Joined Nov 13, 2015
1,083
I'm sure it is possible to predict, but I don't know how. (I'm a tech, not an engineer and I do things 'hands on' :)).
 
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