A common method of making Noise Figure measurements of a receiver is to use a noise generator of known noise power. The output power of the DUT is measured with the generator off (NoiseLo) and on (NoiseHi), a Y factor calculated, and from that Noise Figure is calculated.
G5RV antenna figure prominently in many online forums.
At (eHam 2014) W6OGC describes his G5RV antenna system.
102′ center feed point at 32′ drooping off on each side to 12-15′, 31′ of 450 ohm twin lead, fed with ~130′ or so of RG-8X through a 1:1 current balun at the base of the mast, aligned roughly N-S. On no band is it resonant nor has SWRs less than 3 or so to 1…
Though a G5RV is commonly thought as a ‘no tune’ antenna, just make it to the dimensions in the book, the above shows a possible outcome.
Above is a clip from W4HBK’s 40m grabber today, the signal is VK2OMD running 5W QRSS6 over a 14,700km path. We can infer (Duffy 2012b) from the 15dB S/N in that capture in 0.25Hz noise bandwidth, that in an 800Hz CW filter for say -5dB S/N (threshold of copy) we need 15dB more signal, or 160W for reliable copy. (Less power may be adequate for very short QSOs at the peak of fade cycles.)
Multi band antennas are compromises more so than most mono-band antennas, and part of that compromise is lower efficiency. Often the lower efficiency aspect is accepted without understanding.
Simple keyer with accurate timing for QRSS beacon
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.
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.
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.
(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).
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.