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|golfguru||Posted - 4 December 2012 16:6 |
No diode - ac voltmeter across inductor:
(r) = 19 ohms (80%)
Diode with 180k resistive load:
R = ~76 ohms
Mmmm ... you beauty ... antenna Z of local (963kHz) might be around 75 Ohms - matches my test gear impedance and coax test leads.
Edited by - golfguru on 12/4/2012 4:14:03 PM
|golfguru||Posted - 6 December 2012 15:44 |
Mmmm.... the info in this thread migrated to my other "antenna resonance" post.
Back here now.
Don't know about this app now:
It would appear, if Zim's calculation of my antenna/ground /Z/ (57.5 Ohms) is correct, that my original premise of reducing the voltage across the inductor by 70.7% with an additional series resistance was correct.
Anyway, moving on:
I included a capacitor in the series tank this time to make it easier to peak signals.
Measuring the RF ac across the coil without a load would be the best method but it requires a high impedance RF voltmeter. My "Ballantine 303" has 10Meg input Z and is good to a few MHz.
Measuring the 70% drop across the 120k, noninductive resistor, as the diode load, at DC, using a digital voltmeter is within the average hackers reach.
Points to watch?
* The method only shows the apparent /Z/ at the tuned frequency.
* Different diodes may require different loads to be accurate - might even vary with frequency or signal power.
Others may like to comment and/or run some of their own tests at different frequencies which I am not able to do with my lack of stations (1 only).
PS: Zim's resistor substitution method may be the most accurate "hacker" method if a simple formula could be produced.
Edited by - golfguru on 12/7/2012 1:06:28 AM
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