Re: LF: Ferrite RX antennas

["James Moritz" <james.moritz@btopenworld.com>]

Dear Stefan, LF Group,

> What do you think about the 50 Ohm output winding and a separate resonated 
> winding?
In this case, no... the 50R input preamp would have a higher noise figure, 
considerably lower gain, and require more experimental adjustment. If you 
use the high Z buffer type of circuit in conjunction with the high resonant 
impedance of a parallel tuned antenna, you can more or less guarantee a low 
noise figure,  high power gain, good linearity and reasonable power 
consumption with a simple circuit.
> Would you try either 2x7 rods or 3x5 rods? Both would fit in my backpack. 
> If i read your explanation, a longer rod would be an advantage...
Increasing length increases signal level, but reducing area reduces signal 
level... I am not sure which combination would be better, but for these two 
arrangements the difference probably would not be very great - probably this 
is best found by experiment. 3 rods end-to-end would be a less convenient 
length to handle, though.
In my experience, using the stranded wire would be an improvement over solid 
wire, even if it is not "proper" litz construction. If you go for a fairly 
high tuning capacitance, and a single layer winding, the insulation is 
probably not very critical, but I would include some insulation between the 
ferrite and the wire, since ferrite is a poor dielectric, and also the 
abrasive surface might damage the thin enamel on the wire.
Cheers, Jim Moritz
73 de M0BMU