At 11:33 AM 7/27/04 -0600, you wrote:
Hi,
I got given some poly square plastic stuff and thought hmm I could use this
in a loop somehow and this popped into my mind I am thinking 15 inches on
the outside with wood and the lengths on the inside holding it together that
poly square plastic stuff is 1/2 inch square. So that would make the loop
14.5in square not huge but decent I figure. I was thinking of bringing the
coupling loop in about an inch or two from that so the coupling loop would
be 13.5in or so to 12.5in not sure which is better. was going to make the
"plate" to hold the cap out of lexan and the "plate" for the connections
back to the receiver. question is how many turns of wire for the AM BCB I am
sure there is a calc for this but I haven't seen it and I wanted to share my
design. Also the rest wood be made from wood the longer pieces.
Scott
KC7WDG
I have a BCB loop constructed on a plywood rectangle 10 1/2" x 14". I placed a 2" peg at each corner. I wound 16 turns of Radio Shack hook up wire around the pegs.
The plywood sheet is mounted vertically on a wood block which acts as a base. I mounted a 365pfd capacitor in the center of the sheet on the side opposite the windings. My Hi-Fi set came with a BCB antenna which consisted of a small plastic hoop about 8" in dia. with 3 turns of wire on it. I use this small loop as the pickup loop for my tuned loop. I attached this 8" hoop to the sheet the centre of my tuned loop. The 8" hoop has a twisted pair about 2' long terminated in spade lugs.
Under normal BCB receiving conditions I have the tuned loop sitting on top of my HI Fi set with the twisted pair connected to the antenna input on the receiver. When I tune the loop to the received station the difference in reception increases a quantum leap.
When I attempt DX reception with this tuned loop and a portable receiver out in the garden (minimize the local noise) I find that the placement of the pickup loop inside the tuned loop provides too much coupling. At first I dismounted the 8" loop and moved it farther and closer by hand to find the optimum coupling which is a balance between best selectivity/signal strength. I soon got tired and mounted one end of a 12" dowel to the plywood sheet and just hung the 8" pickup coil on this 'peg'. I could shuttle it from inside the loop to about 10" away from the loop. What I find is that under certain conditions ... eg separating close stations .... the pickup loop works best hanging on the peg up to 8" away from the tuned loop! I find that the placement of the pickup loop is almost as critical as the tuning of the main loop itself.
One of the advantages of making the tuned loop relatively small is that it is portable. I would not be able to put a 4' loop on the table out in the garden hi. Another thing you might want to experiment with is using your tuned loop with a longwire antenna and ground. I have a longwire available out in the garden and I connected it to one side of the tuning capacitor. A ground wire was connected to the other side. The reception increases a second quantum leap. Again adjust the tuning and coupling for best reception ..... you will be amazed at the daytime reception with this setup. I say daytime because night time reception is completely different with all kinds of different stations coming in on skip. All my BCB DXing is daytime.
So back to your questions:
your loop will be about 13.5x12.5 ..... mine is 10.5x14 and it uses 16 turns.
your pickup loop mounted inside the loop ...... mine is variable and some conditions works best at up 8" away from the loop!
Jim Dunstan
Thunder Bay, ON
