On Thu, 13 Jan 2011 11:05:38 -0600, "amdx" wrote:

This is in regard to a crystal radio, so the match is for a low impedance
antenna to a high impedance tank circuit.
The antenna: R=58 ohms C=1072 ohms at 1Mhz.

Hi Mike,

Is this a fantasy antenna?

For the 58 Ohm resistive value, it would have to be about 300 feet
tall - not the size of operation one usually comes to expect for a
Xtal radio aficionado.

If it is that tall, it would exhibit 200 Ohms Inductive reactance (one
fifth of what you report, and the opposite sign).

Something doesn't wash here.

I calculate an 18.5pf cap for the match, making the antenna look like 58R
and 17pf.

58±j17 Ohms is still a complex impedance, and says nothing of match
which can only be expressed in terms of the expected load R.

And I now have a 1.5 Mohms source feeding a 1.5 Mohm load.

How that is arrived at is something of a mystery. By the numbers, you
describe a 26000:1 mismatch.

The purpose of which is to cause minimal loading of the tank by the antenna.

Well, what you have described is sufficient mismatch to insure that.
The English reading of your sentence also is instructive: the tank is
isolated from the antenna, i.e. no signal is passed to it. This seems
to be counterproductive in regards to detection.

I don't understand how adding a series capacitor makes a parallel
conversion.

Haven't we been down this road some months ago?

73's
Richard Clark, KB7QHC