Posted In: Technique
Good day friends, since at my new QTH there is only the possibility of an antenna under the tiled roof, I want to ask if anyone has experience with this, whether it is worth dealing with at all. It would be about a multiband vertical approximately 3m long.
Thank you in advance for any responses
Stefan OM4TW
Hello,
far better than a three-meter 'multiband' will work any magnetic loop antenna. It can also be easily hidden under the roof and the magnetic field passes through the roof covering even better than the electric field from an extremely shortened radiator. Not to mention the interference to surrounding equipment in the house with high intensity E field.
Given today's state of technology, remote tuning of the mg. loop can be done easily, copper pipes don't cost much...
73, UHU
Hello Števo, I have a 4-element Yagi under the roof for 2m and there is no problem with any attenuation. The roof construction is wood, foil, and tiles. Rather, surrounding objects that are part of the attic space and the height of the antenna above the floor, distance from the tiles, lightning rod on the roof will be problematic. The antenna's properties will certainly change, but I say that a bad antenna is better than none.
Just a funny tip.
The mag loop is an excellent antenna, but it has its small flaws.
Especially the control, split capacitor, very strong near field, very high voltage on the capacitor plates.
It works, remote control can be made at home on the knee, but it is quite labor-intensive.
If it is about an 'invisible' antenna, or simply an antenna in the attic, I rather recommend using a remote-controlled tuner for less labor, preferably SGC, which can tune low-impedance loops, various shortened antennas, etc.
If possible, use the largest possible loop circuit, or make more turns, or even make a horizontal loop.
It will not be worse, but neither significantly better than a mag loop.
But the bandwidth of the entire antenna, if it has at least 5 or more meters on a side of the square, gives the assumption that it will somehow work from 80m to 6m.
If 2 turns are used and the square has at least one side of 10m and the other is not less than 8m, it works from 160m as a compromise, but the 80m band is almost like a poorly stretched dipole.
The advantage is that tuning is practically automatic, no fine-tuning is necessary, it is instantaneous for transitions across all bands, without waiting, it is in the memory of the tuner.
The efficiency is not that great, but if sufficiently thick conductors are used, 2.5-4mm2 losses are acceptable.
http://www.sgcworld.com/239PROductPage.html
This tuner is actually designed for similar applications.
The cheapest version deserves at least a food box that has latching locks or a waterproof installation box.
For control, it is enough to run an FTP or UTP cable, it can reliably power and control this box up to 100m.
http://www.sgCWorld.com/Publications/Manuals/239man.pdf
It can be used in many ways, it is a quick way to do it at least somewhat well, without the need for compromises and wiring the surroundings.
The biggest advantage is that by distributing the signal via coax from the TRX, we work with minimal losses, as the distribution of the signal from the TRX to the remote tuner is tuned, coax does not radiate.
Of course, a full-size antenna is a real antenna, but when that's not possible, it's a cheap and quick way to make it work without the need for uncertain results and tinkering.