Category: Antennas

The nature of radio signals received off-air is that they are accompanied by undesired noise.

A key measure of the ability to decode a radio signal is its Signal to Noise ratio (S/N) at the demodulator (or referred to some common point).

We can speak of think of an external S/N figure as \(S/N_{ext}=10 log\frac{S_{ext}}{N_{ext}}\) in dB.

Receiver systems are not perfect, and one of the imperfections is that they contribute undesired noise. Continue reading Signal to noise degradation (SND) concept

A recent online discussion tried to advise on the need of a common mode choke on a UHF Yagi.

Above is the subject M2 440-6SS, 420-450 MHz Yagi deployed in vertical polarisation (using the other pair of holes for the U bolt). Continue reading Gamma matches get blamed for a lot of stuff

A correspondent asked about the difference between two small untune loops mentioned in two of my articles, this article explains.

Firstly lets set the context, a small loop means less than λ/10 perimeter, and untuned is to mean that the loop is loaded directly, in this case by a receiver which we will assume has an input impedance of 50+j0Ω.

Let’s look at the two cases. The key difference is in the connection at the gap:

• the first has a short circuit coaxial stub of half the perimeter between the inner conductor at the right side of the gap and the outer surface of the outer conductor at the right side of the gap; and
• The second directly connects the inner conductor at the right side of the gap and the outer surface of the outer conductor at the right side of the gap.

Small single turn un-tuned shielded loop

Above is a diagram of the loop. Continue reading Differences in two similar simple untuned small loop configurations