In article , Robert Casey
wrote:

Just posted a schematic of the Miller TRF receiver, with the "secret"
inductance values filled
in. a.b.p.radio


Hi Robert, that's certainly a cute little radio you have there. An
interesting point is that the separate "negative mutual coupling"
inductance, the one with the "secret" value, isn't even necessary and the
part can often be eliminated from the circuit. All you need to do is wind
L1 and L2 like a typical double tuned IF transformer, and if the coupling
coefficient is correctly chosen to yield the required value of mutual
inductance, and if the two windings are phased correctly to make the
mutual inductance "negative", then the separate coil like you used isn't
necessary, although you must retain the capacitor in the common lead of
"L1" And "L2", since that is part of the "secret". This scheme will work
in a circuit like the Miller "High Fidelity" Crystal Tuner where L1 and L2
are just single winding coils, there would obviously be problems applying
the idea to your circuit because of the extra winding you put on L1,
making it into a transformer by itself.

I listened to the WABC "jpg" you posted, and the tuner certainly has a
good bandwidth, although I wonder how much pre emphasis WABC might have
been using and how well your receiver matches it, I will have to listen to
it again to see how correct the de emphasis seems to me, there was also
some background noise at several points, I will have to listen again to
see if it was part of the audio at points, or if it was interference of
some sort. The thing I didn't like about it was that it had pretty
horrible levels of distortion, and while this could be WABC's fault, I
have found that it is typical of these so called "High Fidelity" crystal
receivers. I have a couple of J.W. Miller "High Fidelity" crystal tuners,
and they have the same distorted sound. I think this is because the
crystal detectors produce really horrendous distortion, unless you have a
big enough antenna to get the audio output level up to at least the 2
volts RMS that Patrick recommends. I would try for another 10 dB or so of
audio output above that level before being completely happy myself. But
no way do these simple crystal sets sound "High Fidelity" to me because of
all the nonlinear distortion. The distortion probably does help give them
their bright sound though, sort of a psycho acoustical trick if you will,
but it does wear on one.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/