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.)
Continue reading Simple Morse beacon keyer updated 2014/03/01
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.
Continue reading Simple Morse beacon keyer for VK3FI on 600m
This series of seven articles has:
Continue reading Designing high performance VHF/UHF receive systems – Part 7
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.
Continue reading Designing high performance VHF/UHF receive systems – Part 6
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
(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
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
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
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