Below are images of an antenna I have owned over 45 years and my guess is it was built shortly after WW2. Obviously, it's home-brew and when I bought it I was told it was designed to work best between 15 and 10 meters by the ex-US Navy "electronics man" who built it and sold it to me. It is perfect to use it to locate Citizen Band 11-meter "good buddies"
... especially those who were NOT good buddies
many years ago ...
I used it on the 10-meter Ham band (the band was out/no solar flares) only twice to "find" two (known) local transmitters (a W7 and a K7) and on the 15 meter Ham band to "find" the same local transmitters plus a K3 "portable-7". Dialing in the variable capacitor at the top of the Loop is ABSOLUTELY CRITICAL or this Loop is completely dead (not resonant).
BUT ... this should be THE hall-of-fame Loop antenna for 11 meter cbs'er "rabbit hunting'. Compared to a 9 foot whip (quarter wave) on a car, believe it on not this Loop is only around 15dbd down (no way to prove this) making it an amazingly live antenna. I used this Loop many times for 'fox hunts' to find CB mobile (stationary) CB radio transmitters as far as 12 miles distant and this Loop was the best/most accurate/most "awake" antenna of different Loop versions we worked with.
With this Loop tuned (peaked) for receiving and with a Johnson "Matchbox" in circuit it was (is) an amazing bi-directional mobile transmiting antenna ... yes, comparatively short range but absolutely bi-directional and VERY narrow beam width.
My question: since this Loop is just under 10 inches in diameter and can be made resonate AND directional as well as "awake"
when the (received) wavelength is 36 feet @ 27 mHz ... does the actual size of a loop matter? If frequency range is based on breaking a Loop of any size on top and adding capacitance (or possibly inductance (???) - how do we determine those values?
Post 1 on this thread shows an open Loop mounted horizonally. When the same
Loop was closed (later post) there was no change in his TV reception. <--NOTE: here are TWO variations for Loop design.
Above, I posted a photo of a test antenna completed / closed "bottom-fed" Loop via a standard 300:75 ohm balun. <--- 3rd design.
The Loop antenna shown below is 'broken' at its' top and capacitance is added in the gap AND it is fed via a Gamma "matcher" much like many transmitting Yagi antennas.
*Regarding the following photos, please note -
This is a 4th variation
on the Loop Theme
posted here --- so far.
The second photo shows the antenna pointed AT
a transmitter -- NOT broadside but with the Loop almost
aligned "sideways". The suction cup and spring steel goodies on the base are meant to clasp a side window on a car. Does anyone else have other variations to contribute and/or experiences and/or other designs and details?