Designing high performance VHF/UHF receive systems – Part 7

Summary

This series of seven articles has:

  • explained the meaning and value of G/T as a single metric for receive system performance;
  • defined and explained the G and T terms;
  • explained the relationship between Teq and Noise Figure;
  • explained how to analyse simple cascaded stages and hence more complex networks;
  • described how to estimate transceiver Noise Figure and Teq;
  • demonstrated application of the analysis techniques to a set of practical configuration options to provided quantitative comparison of the S/N performance of the options; and
  • discussed measurement of G/T as a means of validating system performance.

Continue reading Designing high performance VHF/UHF receive systems – Part 7

Designing high performance VHF/UHF receive systems – Part 6

Measurement of G/T

G/T can be measured using celestial noise sources provided the antenna can be pointed to them. The noise source that is most appropriate will depend on expected G/T, frequency, time etc.

Sun

Continue reading Designing high performance VHF/UHF receive systems – Part 6

Designing high performance VHF/UHF receive systems – Part 5

Bringing it all together

This part explains how to build a model of the entire receive system to calculate G/T.

Firstly, make an inventory of all of the system elements that you intend to model.

A model needs to be no more detailed than is necessary to provide adequate accuracy for the purpose at hand.

Continue reading Designing high performance VHF/UHF receive systems – Part 5

ARRL Test Procedures Manual (Rev L) – Noise Figure calculation

(Allison et al 2011) detail the method used by the ARRL in their test reports on equipment.

Effectively they calculate NF=-174+27-MDS where MDS is measured in the CW mode using the 500 Hz, or closest available IF filter (or audio filters where IF filters are not available).

Continue reading ARRL Test Procedures Manual (Rev L) – Noise Figure calculation

Designing high performance VHF/UHF receive systems – Part 4

Finding transceiver Teq

We have explained how to calculate Teq from Noise Figure, but most transceiver specifications do not give Teq or Noise Figure directly, in fact they don’t really contain sufficient information to reliably calculate Teq or Noise Figure.

Credible equipment reviews might provide an estimate of Noise Figure or Teq.

The best approach is to directly measure Noise Figure using a known noise generator and the Y Factor Method.

Continue reading Designing high performance VHF/UHF receive systems – Part 4

Designing high performance VHF/UHF receive systems – Part 3

Relationship between Teq and Noise Figure

In the last part, the meaning of the equivalent noise temperature of an amplifier was given.

Whilst you will find that working in Teq has advantages for this analysis, amplifier specifications may not give Teq, but may give Noise Figure.

Continue reading Designing high performance VHF/UHF receive systems – Part 3

An inexpensive current limiter for flashing and initial testing of ESCs – Mk II

There is a risk of damage when flashing ESCs. It accrues from the fact that ESCs have a three-legged H bridge and if a high and low FET are turned on simultaneously, damaging currents may flow. In fact, this can be an issue if the FETs are on together for just microseconds on each PWM cycle. Loading the wrong hex module is a recipe for disaster, it may turn on FETs in an unexpected way.

So, for safety, the ESC should be powered from a current limited power supply during flashing and initial motor testing.

In a process of continuing development, this article describes a variation on the inexpensive current limiter for flashing and initial testing of ESCs – Mk I.

Continue reading An inexpensive current limiter for flashing and initial testing of ESCs – Mk II

Designing high performance VHF/UHF receive systems – Part 2

G/T is defined as the ratio of antenna gain to total equivalent noise temperature.

For clarity, lets define those terms.

Gain

Gain of an antenna is defined (IEEE 1983) as the ratio of the radiation intensity, in a given direction, to the radiation intensity that would be obtained if the power accepted by the antenna were radiated isotropically. (Isotropically simply means equally in all directions.)

Continue reading Designing high performance VHF/UHF receive systems – Part 2