18-11-2018, 07:45 PM
Hi. The plot thickens with these EPAD devices and more so with the ALD110800A. These as I have said are a quad device whereas the ALD110900A are dual devices.
Instead of messing about with the old crystal set I used my tuned 1 meter frame aerial for tests. I've constructed this little detector with matrix board and a toroid to match into the single turn low impedance winding.
As can be seen in the circuit there is a choke after the EPAD, I have found a 470uH choke and 1nF cap (GH & C) works the best with the strongest stations getting the biggest boost. On these stations when tuned in properly there is actually a rise in RF level (more on this in a minute) With just a 1nF cap and no choke the audio is lower and the the RF also falls, I'm using 4K phones. With the ALD110900A dual chip this effect is far less noted, but piggybacking two ALD110800A chips the audio on strong stations is even louder!!!
So I then add in 1.2 volts to "X" plus toward the choke and the cap and minus to the phones and the set howls like a regenerative set, ultra sensitive with the band full including foreign stations, back the voltage off to 100mV and it settles down, the results are quite unreal!!.
I do think these chips are using the DC content from strong stations to give some amount of regen and adding in a little external DC is "helping" the process, With the Dual ALD100900A the effect is far more controllable.
Food for thought with all this.
Now a free radio with very useable results, FM next, could be interesting.
Instead of messing about with the old crystal set I used my tuned 1 meter frame aerial for tests. I've constructed this little detector with matrix board and a toroid to match into the single turn low impedance winding.
As can be seen in the circuit there is a choke after the EPAD, I have found a 470uH choke and 1nF cap (GH & C) works the best with the strongest stations getting the biggest boost. On these stations when tuned in properly there is actually a rise in RF level (more on this in a minute) With just a 1nF cap and no choke the audio is lower and the the RF also falls, I'm using 4K phones. With the ALD110900A dual chip this effect is far less noted, but piggybacking two ALD110800A chips the audio on strong stations is even louder!!!
So I then add in 1.2 volts to "X" plus toward the choke and the cap and minus to the phones and the set howls like a regenerative set, ultra sensitive with the band full including foreign stations, back the voltage off to 100mV and it settles down, the results are quite unreal!!.
I do think these chips are using the DC content from strong stations to give some amount of regen and adding in a little external DC is "helping" the process, With the Dual ALD100900A the effect is far more controllable.
Food for thought with all this.
Now a free radio with very useable results, FM next, could be interesting.
