tuning an antenna coil in a shortwave receiver
Here you hear the effect/necessity of the exact tuning (“peak”) of an antenna coil to the received radio station/frequency. In this case (superhet receiver on 3,5 MHz) it is done by changing the capacitance of a small trimmer/padder parallel to the antenna coil, which is almost ideally tuned in by a few fixed value capacitors in parallel. The “finishing touch” comes from the trimmer/padder that peaks the coil to a specific frequency (=one radio station). When I say “over the coil” I mean …
July 20th, 2009 at 4:45 am
Zo———-”tuning “that aluminium capacitor–peaks and——goes up and down the resonance curve?
Do you use-pre set filters?
Is your radio -mainly for 80 metres?
Is this your-10 metre long wire antenna?
Pre selecting the frequency range-enhances the superhetrodyne “selectivity ”
Steve.
July 20th, 2009 at 4:52 am
Zo-the use of a variable capacitor-can “tweek “to all frequencies on the band?
Just add another knob——to your front panel?
Steve.
July 20th, 2009 at 8:24 am
Yes, it works well. The antenna is adapted maximal/optimal to the frequency. The reason is that the antenna outside (10 meter wire) is too short in relation to the frequency (80 meter). In no other place of the receiver there is more radio signal (gain) to win.
July 20th, 2009 at 10:35 am
Yes, the antenna is tuned seperately. The band filter (antenna coil) at the entrance of the receiver (80 meter, approx 3.5 MHz) is more or less fixed (tunable a bit with a 50 P capacitor). It is indeed only for 80 meters. The antenna is indeed a long wire “horizontal” antenna from approx 10 meter. The circuit enhances the selectivity. There are less or no “mirror frequencies” (litt. translation from Dutch) = same radio station 3 times on 455 KHz further/lower on the tuning scale of the VFO.