Fiberglass

[Tepco]

I never made any thread about flat spiral coils, only mentioned it in some completely unrelated post. Later few people built it with good results and it became popular. Not a problem free design however. Difference in parameters can occur due to different wire type used, internal diameter and insulation thickness etc. Even if you keep physical dimensions (number of turns or ID\OD ratio) constant, wire length may vary for different cable types, affecting coil inductance. Another issue is shielding. Unshielded coil without cable (wire extended some 1.2m and twisted every 2-3cm to connect to control box) is very fast, easily 8uS in unmodified detector, can go below 5 in tweaked version, but shield can affect this significantly. Simple shield (graphite sprayed directly across wire insulation coated with single epoxy layer to keep it compact) and coax cable will slow it down almost twice but this is still fast enough. Using spacers (made of any suitable material to keep shield to coil distance at least 5mm from each side in order to reduce capacitance) can improve speed, in all cases outer coil end and shield goes to GND and inner end to detector connection, otherwise shield will slow it down even more. I prefer this coil type due to simplicity and low cost, without need for machined parts and special material\wire type etc, you can wrap this in 10min. without any tool, but for underwater use more complicated design like described in baum 7154 post can be better. Problem with flat spiral is relatively large surface area, producing lot of drag in water, and if you shield it for high speed you will end up with something at least 1.5-2cm thick, not “hydrodynamical” at all and usually positively buoyant, will tend to float like cork depending on spacer material used.

[baum7154]

The information on spiral coils is referenced in the TARGET TIME CONSTANT threads in posts 32 and 33. In 32 I found Tepco comments on spiral coil in the thread 'HOW TO JUDGE SHIELD EFFECTIVENESS'. In 33 there is a post from TEPCO on a spiral coil contained in a paper on building the SURF PI 1.2.

Regards,

Dan

[Pin Head]

Hi all, I have still not located the pics of a spiral wound coil that I had printed out in the past. Went through all the sites as told, and still
Not found the pics.no big deal I think I have learned enough from reading through all the threads to figure out what I am doing. Thanks for all the help and input. Rob. ((pin head).

[Tepco]

Here it is:
http://www.geotech1.com/forums/showt...061#post149061

[Davor]

A picture there shows a "Dugapol set" which I believe is manufactured in Serbia. I never thought of asking - where exactly are you from? Maybe from my neck of the woods?