H = horizontal, V = vertical.
H = horizontal, V = vertical
Ask your reseller for sets suitable for your application.
Antenna 1 covers the frequency range from 20 MHz to 250 MHz. It therefore includes the ISM band at 27 MHz, and is particularly suitable for interference and spurious signal searching in the VHF broadcast radio range, but also covers the lower end of VHF television and includes DAB frequencies.
The principle for this frame antenna is an old one: back in 1971 Sony patented a special version for TV reception (US Pat.3573830). Narda has specially optimized the design to generate a relatively narrow major lobe in the directional diagram at frequencies of up to 250 MHz. The light metal frame is crimped to give it stability.
The principle is based on combined measurement of the electric and magnetic fields.
The sensitivity of the antenna to the magnetic field components appears in the directional diagram as a horizontal figure of eight. This in itself would allow direction finding, although there would be an ambiguity of ±180° in the bearing result. For this reason, the voltage generated by the electric components is also utilized. Here, the frame is used as a dipole, which is possible as long as the dimensions are small compared with the wavelength. The reception characteristic for the electric field in the horizontal plane is a circle without any predominant direction. Superimposing both voltages results in a cardioid characteristic showing a broad maximum in the main direction and a minimum in the opposite direction.
The antenna also works when oriented horizontally: Here, the electric field strength has a figure of eight characteristic and the magnetic field a circular one, resulting in a very similar cardioid.