On Nov 15, 1:59*am, "amdx" wrote:
Hi Guys,
*Assuming I have a tank circuit on a crystal radio with a Z at resonance of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.

I did take part in the discussion of matching, but I am afraid you are
off by several orders of magnitude regarding the impedance value.

Say you shoot for resonance at 1 MHz: a 2.5 mH inductor (already
impractically large) and a 10 pf capacitor (already impossibly small)
will resonate close to 1 MHz but have an impedance of 16 kilohm or so,
100 times lower than your assumption.

For 10 MHz, it would be 1 pF and 250uH, again for 16 kohm.

In practical circuits the impedance is typically in the order of
300-2000 ohm.

A typical old-style mediumwave tuning capacitor has a maximum
capacitance of 360 pF to tune about 520 kHz at 850 ohm with a 260 uH
coil.

Assuming you use a much smaller than usual 100pF variable, say 130 pF
including tray capacitance in the coil, at the bottom of the band you
will need 760hH, and get 2.5 kiloohm.

On shortwave, let's say yo want to tune a lowest frequency of 6MHz
with only 60pF all included - again, nobody does that - you need 12uH
inductance but only get 450 ohm impedance.