H-field active loop antenna
- Easy to use mount near ground level.
- Encapsulated for outdoor use
- Very compact size: 1.3m diameter
- Easily transported
- Noise immunity to electrical field interference
- Easily located away from local interference sources Isolated from mains borne interference
- Survives RF fields of 13V/m
- No tuning
- No inconvenience
- No band changing elements
- Narrowband/ VLF version 30-300KHz
- Predictable performance
- Computer optimised design
- Extremely broadband 10kHz -30MHz
- Sensitivity set by received background noise
- High linearity complementary push pull amplifier
- Good response to high angle and low angle DX
- Deep broadside nulls for ground wave signals.
- VLF time and frequency receiver
- EMC & EMI testing.
Principles of operation
The principle of operation is that an RF voltage appears across the terminals of a loop when it is placed in an electromagnetic field. This voltage is proportional to frequency for a given field strength. Therefore at Very Low Frequencies, the voltage is very small, and requires greater amplification.
The new TL Loop uses a unique feedback system to optimise the amplification factor. The method uses a loop constructed of transmission line in which the line is also part of the feedback system.
The antenna is broadband and requires no adjustment other than orientation since it has deep broadside nulls for "Vertically polarised ground waves. There is no null in the vertical direction, as with whips, so that short hop high angle sky wave reception and long hop low angle reception can both be excellent.
Best results are obtained with a clear site. No radio frequency grounding of the antenna is required.
A perfectly lossless antenna picks up more ambient noise, due to atmospherics, interference, etc., as one goes down in frequency. Such high levels of signal and noise can be considerably attenuated without seriously affecting the overall signal to noise ratio. In other words a smaller less efficient antenna can be used just as effectively coupled with a low noise amplifier.
Active antennas therefore do not produce high signal levels but nor do they need to; S/N is what counts. It is preferable that the antenna is positioned vertically, just above ground in an open area. Being an antenna which responds to the magnetic field component, it is highly immune to capacitively coupled local interference which is a common problem of active whips, and local interference can be reduced either by nulling or by relocating the antenna far away.
The antenna is highly portable yet may be permanently installed outdoors.
Permanent support is easily arranged by attaching the loop to a circular hoop on a short pole. The power requirements are 12V at 50mA. This is fed via the coaxial cable from the receiver using an 'isolating T' section.
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