An Unamplified Four Foot Box Loop

Dear Fellow BCB DX'er

Please find attached your copy of my four foot unampilfied box loop. It will
tune from 525 kHz to about 1710 kHz covering the entire Broadcast Band.

The umbrella stand described in the article is the type you would use for an
outdoor umbrella. I fill mine with sand to keep it sturdy You will also notice
a lack of metal hardware in this design. This was done on purpose to keep the
antenna's pattern as clean as possible. Other designs you may see have a lot
of metal in them and this will lower their ability to null and to pick up weak
signals. This is a DX'er's loop. If you wish to save space you can make the
cross arms one foot smaller or 33.5 inches long. It will still work but not as
well. You may also have to fool around with the windings to tune the entire
band.

Have fun building it and lots of DX using it. Any further questions can be
sent to me via:

Mail Shawn Axelrod
30 Becontree Bay
Winnipeg MB R2N 2X9
E-Mail Saxelrod@mb.sympatico.ca

Shawn

REMEMBER ON A CLEAR DAY YOU CAN HEAR FOREVER

I have been using a three foot box loop that Don Moman in Edmonton, Alberta put together for me for several years now. I have been more than happy with its performance, and I have a long list of leggings to prove it, However I have been wondering how a four foot loop might help out my DX'ing by producing either a better signal or deeper nulls. I set out to build this four foot model in every way. My four foot loop did carry on one important idea that Don Moman's loop had and that was the less metal the better. The four footer has as does the three footer only four screws and two bolts. The rest of the loop is wooden thus keeping the antenna's pattern as true as possible.

Parts

Preparation of the Various Parts

As I used mostly 2 x 2 cedar to construct the loop my measurements are based on these sizes. Should you use another type of material your measurements will have to change accordingly -

A. Cross Arms

To form the cross arms find the center of the 45 1/2 inch long 2 x 2's. Measure 3/4 inch on either side of the center. Shade this area as per Figure C. Then cut out the shaded area to a depth of 3/4 inch. By doing this to both arms you can fit them together to form a perfect cross with both arms on the same plane.

B. End Pieces

To start with take each of the four 7 inch 2 x 2 pieces and mark off 1/2 inch spaces. Draw lines across the face of the wood on the 1/2 inch marks to produce 13 lines 1/2 inch apart. Take a saw and make a cut about 1/8 inch deep on each and every line. This will give 13 equidistant grooves on the top of each of the four end pieces, as per Figure A. Now on the side opposite the grooves you have to make a cut similar to that, you make on the cross arms. Find the center of the end piece and once again measure 3/4 inch on each side on center. Shade this area as per Figure B and cut out this area to a depth of about 1/4 inch deep. This will form a cut that will fit the ends of the cross arms. Next you have to drill, a hole in the exact center of each end piece as per Figures A and B. It is important you do this carefully so the end pieces will fit properly to the cross arms.

C. Braces

To form the braces as shown in Figure E drill two holes on the flat side of the 6 inch 2 x 1 wooden pieces. Each hole should be centered one inch from the end. The holes should be drilled to a size that will fit the bolts you are using.

D. Dowel Stand

Figure F shows the 3-3 1/2 foot long 1 1/2 inch diameter dowel and the 4 inch long piece of 2 x 2. To make these two pieces fit you must cut a piece off of the dowel. Cut a 4 inch long 1/2 inch deep piece of the dowel to form a notch that the 2 x 2 piece will sit on. Take the 2 x 2 and drill a hole through it about 1 to 1 1/2 inches from the top end. This hole should take the bolt you chose to use.

Assembly

A. Dowel Stand

Take the 2 x 2 piece and fit it into the notch on the dowel, once you are sure it will fit well glue the two pieces together with a good wood glue. This dowel stand will fit into the outdoor umbrella stand and rotate with ease.

B. Tuning Board

Take the 6 inch long piece of 1 x 2 as shown in Figure D and mount your wire connector 1-2 inches from the end of the board. On the underside of the board mount your variable capacitor so as to keep it close to the front of the board. The shaft must stick out in front of the board so a knob can be attached.

C. Mounting the End Pieces

Attach each of the four end pieces to the ends of the cross arms. First of all fit the two cross arms together to form the X. You van use wood glue to keep them together. If you feel the need a 1 inch screw can be put in also. Insure that you put the end pieces on so that you can wind the wire around the outside of the loop as per Figure G. Glue and screw each end piece on securely.

D. Mounting the Tuning Board

Mount the tuning board on the top side of any of the end pieces. The bottom side is the side with the grooves on it, so by gluing the tuning board onto the top you will in no way interfere with the grooves. This end is now the bottom of the loop as per Figure G.

E. Mounting the Braces

Take one of the bolts and put it through one brace as in Figure E then through the piece of 2 x 2 as per Figure F and finally through the second brace. Secure the bolt using the nut (I used a wing nut to make it easier to adjust). You now have a stand with a rotating and tilting mechanism. The stand may have to be weighted to keep it stable. Sand works well and lasts forever.

F. Mounting the Loop

Slide the loop between the two braces and see where it would balance for tilting without hitting anything such as lights in the ceiling. I drilled a hole 17 inches from the center of the loop on the bottom arm with the tuning unit. You can slide the second bolt through the brace, the loop arm and the other brace. Secure it with a nut and your loop is now mounted on the rotation assembly as per Figure G.

G. Pick Up Loop

In order to put on the pick up loop you must drill a hole 3 1/2 inches from the tip of the loop in each arm. The hole need be only big enough to feed your wire through. The pick up loop is wound around the inside of the loop. You will have to drill one extra hole on the bottom arm 1 inch above the first hole. Attach one end of the wire to your connector and then wind the wire through the holes until you reach the bottom again. Keep the wire fairly tight so you don't get too much slack, The second hold on the bottom is your final hole and then attach the end to a separate section of your wire connector. These two ends must not touch.

H. Winding the Loop

To wind the main coil of the loop solder the end of your wire to the solder lug on the variable capacitor. Then wind the wind around the loop pushing the wire into the grooves on the end pieces. After you have completed the winding attach this end to the frame of the capacitor with some solder.

I. Attaching the Coax Feed Line

To attach the coax to your loop have some of the shield as well as the center wire. Attach the center to one end of the pick up loop and the braid shielding to the other end of the pick up loop. Check to see that these two connections are solid and that each side is isolated from the other. In order to get a better match I attached a 680 pf capacitor to the center feed between the center feed and the pickup loop. Do not attach this to the braid of the coax. The loop is now assembled and ready to tune.

Tuning the Loop

First step of course is to attach the coax to your radio. Turn on the radio to around 1000 kHz. Tune the capacitor to peak the signal even if it is first static. Now go up and down the band re peaking the capacitor to see what its true range is. You will most likely find you cannot tune to the top of the band. If this is the case, take one winding of f of the loop. Tune around again to see how high and low you can tune using the capacitor. With the plates meshed in you should be able to tune to about 520 kHz and with them out you can go to about 1700 kHz on my model. You may have to remove 1-3 windings until it will tune the range you want. Make sure you take windings off of the front and back of the loop to keep it in balance.

You are now ready to enjoy the loop to its fullest. By carefully rotating and tilting your loop you can see how deep a null you can produce. I have been able to produce some nulls up to 40 db on my S Meter.