13-11-2012, 04:58 PM
Hi Joe, the scope or meter is much better than your ears (Fletcher Munson Curve)
Loose coupling is as you have already worked out, two types, inductive and capacitive, for inductive just a few turns of single strand insulated wire, you can make the diam. so that it slips over the end of the ferrite rod, it must not be too close to the aerial coils that are on the rod, connect the sig gen to the two ends of your coil but be aware of any loading this might put on the generator as on some generators terminating the output with a very low impedance load can damage the attenuator, try sticking a 75 ohm (or there abouts) in series with the coupling coil as most generators will deliver max power into that value load no problem.
Capacity coupling, used for direct injection, if injecting direct to a tuned circuit then the value of the capacitor can effect the resonant frequency if it is to high a value, for injecting direct to a tuned circuit try a mimick capacitor, a couple of 2" lengths of single strand insulated wire, twist together along the length and leave approx half inch untwisted, strip those two ends back, connect one to the circuit and one to the sig gen, untwist bit by bit to reduce the capacitance and hence the loading, if you want a posh job then use an adjustable trimmer capacitor, make it up in a small box or tin.
Lawrence.
Loose coupling is as you have already worked out, two types, inductive and capacitive, for inductive just a few turns of single strand insulated wire, you can make the diam. so that it slips over the end of the ferrite rod, it must not be too close to the aerial coils that are on the rod, connect the sig gen to the two ends of your coil but be aware of any loading this might put on the generator as on some generators terminating the output with a very low impedance load can damage the attenuator, try sticking a 75 ohm (or there abouts) in series with the coupling coil as most generators will deliver max power into that value load no problem.
Capacity coupling, used for direct injection, if injecting direct to a tuned circuit then the value of the capacitor can effect the resonant frequency if it is to high a value, for injecting direct to a tuned circuit try a mimick capacitor, a couple of 2" lengths of single strand insulated wire, twist together along the length and leave approx half inch untwisted, strip those two ends back, connect one to the circuit and one to the sig gen, untwist bit by bit to reduce the capacitance and hence the loading, if you want a posh job then use an adjustable trimmer capacitor, make it up in a small box or tin.
Lawrence.
