This is a updated collection of easy to build projects for radio amateurs and swl's. See all my projects in the OLDER POSTS down this blog.
Have fun.
73' John

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Sunday, February 14, 2016

Wall Loop 20m.

A stealth solution for apartments .
This max. size open loop antenna for 14 MHz with a totall circumference of 6m. ( 19.68 feet )  is designed to attach to a wall . Not sutable for reenforced concrete walls . It has a no tune bandwidth of more than 300 KHz with a centre swr of 1 : 1.1.  A capacitor was put over the feedpoint to shunt up the feedpoint impedance. The 150 pF parallel capacitor was the best value in my situation ( brick wall ) but can be replaced by a 500 pF tuning capacitor in order to find the lowest SWR at resonance in any setup. First contacts gave good reports in Europe. Although a lot of the hf power is absorbed by the wall, the results are surprisingly good. A test was made with 100 Watts without arcing however 5 Watts are more than enough for indoor use...
The top capacitor is made of twisted pvc coated antenna wire or a piece of 25cm RG-213 coax and is cut for tuning to the frequency . This antenna can also be build on a fibreglass or wooden frame in a diamond shape for field or attic use. Loop circumference for other bands:
30m  : 7m
20m. : 6m
17m. : 4.8m
15m. : 4.2m
12m. : 3.5m
10m. : 3m
Tuning steps :  Change the length or the turns of the top capacitor to tune the loop to the desired frequency then put a 500 pF tuning capacitor over the feedpoint and look for the lowest swr.
You can replace this capacitor by a fixed type.
Follow the thread on QRZ.com :https://forums.qrz.com/index.php?threads/wall-loop-20m.511714/
See de Walloop at DK9JC : https://www.dk9jc.de/blog/equipment/128-20m-indoor-loop-nach-pd7maa 

The capacitor . A piece of RG-213 coax can also be used
Verry good SWR
Feedpoint with 100pF and 47pF in parallel. Notice the line choke.
The loop made by  SP3BGD


SP3BGD feedpoint capacitor for wide range use
The loop at DB9MAT

Disclaimer:I'm not responsable for any damage due to improper reproduction of my projects.

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