12 votes
Accepted

Why does an "electrically small" antenna have narrow bandwidth?

Short answer: electrically small antennas have a relatively low radiation resistance. With less resistance, the resonance is less damped, meaning a higher Q factor and consequently less bandwidth. To ...
6 votes
Accepted

Does a loop antenna have less susceptibility to atmospheric noise than an open ended antenna?

Your reasoning is not too far off. Say you attach a signal generator to an antenna, and then probe the magnetic and electric fields at many places around this antenna in a test chamber. The ratio of ...
4 votes
Accepted

What does the addition of a shield to a small loop accomplish?

A "shielded loop antenna" is a very misleading name. It isn't an antenna, with a shield. It's an antenna made from a shield, with a feedline inside it. It's commonly stated that the shield blocks ...
4 votes

Optimising a small magnetic loop with 1:1 SWR but little radiation

Small loop antennas require great attention to construction details. This is due to the (in)efficiency of a small loop antenna. By comparison, when constructing a simple half wave dipole, a few ohms ...
  • 18.2k
3 votes

Why is self-resonance important in a loop antenna?

"self-resonance" sounds like not quite the way to describe the issue. The problem is more simply that if the circumference is not very small relative to the wavelength, the antenna is no longer a ...
3 votes

Why is self-resonance important in a loop antenna?

VK1OD compared several small transmitting loop antenna calculators. The author concludes that there are serious errors in the ARRL analysis which have made their way into some (most?) of these ...
  • 7,713
3 votes
Accepted

Optimising a small magnetic loop with 1:1 SWR but little radiation

Getting this antenna to perform, as with any electrically small antenna, is a question of minimizing losses. Without being able to test your particular design it's difficult to say exactly what the ...
3 votes
Accepted

Loop Antenna - configuration?

Adding a smaller coupled loop will have a marginal result. The smaller, coupled loop seen on some small loop designs is there to provide impedance matching. If you wish to improve the gain of your ...
  • 18.2k
2 votes

Why does an "electrically small" antenna have narrow bandwidth?

The prime reason that antennas electrically small in terms of wave length also have useful SWR bandwidths that are relatively small is due to the low value of capacitance of those small antennas to ...
  • 2,892
2 votes

What does the addition of a shield to a small loop accomplish?

This is extensively and accurately covered in a great page by W8JI. It starts: Small Receiving Loops Small loops are often referred to as "magnetic radiators". Folklore claims a small "...
  • 8,340
2 votes

Colocated three orthogonal wire loops for lightning detection network

FORGET the third horizontal (yellow) loop antenna! I finally disabled mine because it caused me no end of trouble with noise pickup and thousands of spurious signals sent to the BT (Blitzortung) ...
  • 7,604
2 votes
Accepted

Colocated three orthogonal wire loops for lightning detection network

The lightning detection antennas are not used in any sense to triangulate or to direction find through any other method such as phasing. The three antennas are there simply to provide quasi 360° ...
  • 18.2k
2 votes

Does a loop antenna have less susceptibility to atmospheric noise than an open ended antenna?

An ungrounded antenna element is subject to precipitation static (P-static) buildup that can result in arcing. At least one element of a dipole is usually without a DC ground reference while if one ...
2 votes

Loop Antenna - configuration?

Larger multi-turn loops with the turns too close together can be degraded by the "proximity effect": the turn in the front (or in the case of a spiral, the outermost turn) may have a certain current ...
  • 7,604
1 vote

Why is self-resonance important in a loop antenna?

As the circumference approaches 1/4 wavelength, it becomes increasingly difficult to tune it, as it is no longer a small loop and starts taking on properties of a a resonant loop, which is tuned ...
  • 4,508
1 vote

Optimising a small magnetic loop with 1:1 SWR but little radiation

I suggest you disconnect the loop from the central part of the variable cap . Instead connect to the other section...you then have a more efficient cap without the losses of the mechanical contact. By ...
1 vote

Optimising a small magnetic loop with 1:1 SWR but little radiation

I understand people like to use coax for antenna experiments but in this case I don't think its a good choice. That outer loop diameter is too small for 40 meters and it is a wire when it really needs ...
1 vote

Colocated three orthogonal wire loops for lightning detection network

A third, horizontal loop, will give you an antenna which is horizontally polarized and omnidirectional in azmith, with nulls in the up and down directions. Would this benefit a direction finder? I ...

Only top scored, non community-wiki answers of a minimum length are eligible