17-11-2018, 07:35 PM
Hi.
Using the posted diagram as reference there are some anomalies. if we put the scope via at least a X10 probe after the aerial coupling cap (10-50pf) we can see the RF carrier, (at least on a strong station) removing the phones increases the the RF level as to be expected, also removing the filter cap 1nf does the same due to RF leaking via the detector, so we are needlessly using energy in the filter cap. So lets dispense with it by adding an HF choke after the EPAD and before the phones this indeed stops the loss from the cap, a 470 pf after the choke to earth/ground then doesn't effect the RF level. This of course is also relevant to Galena or germanium detectors so we are gaining more audio for one additional component. Doing this will slightly also improve selectivity.
Using an ALD110800 which is a quad IC also allows us to move the tap or the extra winding to a lower number of turns, this then means you can then reduce turns on the secondary winding or tap to allow lower impedance phones, always parallel up the elements in these devices. Doing this today has resulted in a little more output on the horn speaker, plus of course the addition of an RF choke. We are now squeezing the most from this simple receiver.
I've now an inkling to try an FM crystal set.
Using the posted diagram as reference there are some anomalies. if we put the scope via at least a X10 probe after the aerial coupling cap (10-50pf) we can see the RF carrier, (at least on a strong station) removing the phones increases the the RF level as to be expected, also removing the filter cap 1nf does the same due to RF leaking via the detector, so we are needlessly using energy in the filter cap. So lets dispense with it by adding an HF choke after the EPAD and before the phones this indeed stops the loss from the cap, a 470 pf after the choke to earth/ground then doesn't effect the RF level. This of course is also relevant to Galena or germanium detectors so we are gaining more audio for one additional component. Doing this will slightly also improve selectivity.
Using an ALD110800 which is a quad IC also allows us to move the tap or the extra winding to a lower number of turns, this then means you can then reduce turns on the secondary winding or tap to allow lower impedance phones, always parallel up the elements in these devices. Doing this today has resulted in a little more output on the horn speaker, plus of course the addition of an RF choke. We are now squeezing the most from this simple receiver.
I've now an inkling to try an FM crystal set.
