How to find proper dumpingresistors for a PI-DD-Coil?

[mschmahl]

How can i find or see, that i have the right sized dumpingresistor for a DD-Coil?

Or is it something similar to this: "place 1k dumpingresistor for RX-windings and watch for smooth curve on output of NE5534 when you adjust dumping for TX-windings"

Did someone use a DD-Minelabcoil on a hammerhead or some other homebuilt? And how good is it?

Greetings from rainy germany.

mschmahl

[kt315]

ITMD in a help http://www.geotech1.com/forums/conte...metal-detector
take the book in a hand and I ill say you a page to read.

[mschmahl]

Have i overseen this? I have the book here.

[Qiaozhi]

How can i find or see, that i have the right sized dumpingresistor for a DD-Coil?

Or is it something similar to this: "place 1k dumpingresistor for RX-windings and watch for smooth curve on output of NE5534 when you adjust dumping for TX-windings"

Did someone use a DD-Minelabcoil on a hammerhead or some other homebuilt? And how good is it?

Greetings from rainy germany.

mschmahl

Balancing a DD coil is more tricky than a mono. Firstly you need to have RX coil roughly damped using a suitable fixed resistor. Let's say, for example, 470R. Then monitor the preamp output with an oscilloscope and use an adjustable resistor network to achieve critical damping on the TX coil. Disconnect the adjustable resistor network, measure its total resistance, and fit a resistor with the closest standard value across the TX coil. Then remove the 470R across the RX coil, and repeat the process (as before) using the adjustable resistor network across the RX coil to determine the correct damping resistor.

[mschmahl]

Thanks a lot for this explanation. I will try this.