As I promised there is another antennas inspiration - receiving loop which I found on internet long time ago. ( Sorry I do not have original link of it but I found original text copy so I am going to share with You. If some of You know the originator then do not hesitate to email me and I will add these information)
I looked for good receiving small size loop so I tried all what I found and which seemed to be usable for me. One of the most popular receiving antennas with small size are different types of 5" to 6" size loops made using the coaxial cable.
160/80m coaxial receiving loop
To construct the 160m loop you'll need 20ft on RG-59. Fold the RG-59 in half. On the 160m loop, it would be about 10ft from the end. On the 80m loop, it would be about 5 ft. from the end. You then mark the center, then measure 1/2 an inch on both sides. Strip away the outer cable, the braid, and then the foil covering the center conductor insulation. I then usually use heat strink to weatherproof what I've cut away.Then cut some schedule 40 one inch pvc pipe into 3 lengths. Each should be 45 inches long. Cut one to 56 inches. That one will be the mast.Assemble the lengths you cut into a "T" configuration.
Measure from the center 43 1/4 inches on the three 45inch lengths. Drill a hole large enough to pass through the RG-59. For the 80m loop. Drill three holes 20 1/2 inches measured from the center of the "T". Loop the 20ft RG-59 through the holes drilled at 43 1/4 inches, then loop the 10ft length through the holes drilled at 20 1/2 inches. Install the male type "f" and weather boots on the RG-59 you just looped through the "T". Attach the 20ft cable to the 160m matching box. Also do the same with the 80m box. I find it easier to aim the 160m box with the SO-239 down. And the 80m box with the SO-239 up. That way the it will keep the harness short. Drill the mounting holes through the box, once you pull the loop tight.To tune the loops, attach each loop separately to your transceiver.
DO NOT APPLY RF TO THE LOOP. This will damage the components, and probably your transceiver. Place the dial of your transceiver to the part of the band you want to use the loop on. Then adjust the the trimmer capacitor for maximum noise. Do this for both loops. Then attach the harness. The loops should be ready for use. I usually weatherproof the boxes and frame. And I add a wood dowling to strengthen the mast.
Construction of the boxes appears as follows:
The trimmer values are aprox. the values shown above. However I've used ARCO 468 for the 160m loop and ARCO 467 trimmers for the 80m loop, with great success. RG8X can be of random legth. I usually cut them to fit between the boxes. The lead to the receiver can be of any length.
I tested this antennas for couple of months on my portable QTH where I had chance to use other antennas and compare them. The signals come from this coaxial loop was significant worse than signals from even short beverage (164m) or from TX antennas like 200m half square or inv.vee but I have to say that s/n was much better as finaly expected.
Comparing to K9FD or other similar loops this type is more complicate to build and tune properly and impedance matching is not as easy as can seems to be if it should work on both LF bands.
In fact I used it as two monoband loops on 160m/80m bands so I did not used the feed line box or splitter as shown above. I did not made any exact measurements but it seemed that an interaction between both loops caused antennas patern.
73, Petr OK1RP