Whilst I’m not a very active radio amateur, I do get on every couple of weeks. During our narrowboat trip on Nokomis, I operated every other day or so and I now understand why. It was sooo much quieter.
By quieter, I’m referring to the background noise that comes through the speaker when there is no discernible signal being received. This noise is a combination of:
- atmospheric noise from lightning discharges and the like;
- thermal noise that emanates from anything with a temperature greater than absolute zero; and
- man-made noise that comes from the plethora of devices we use in our modern lives.
At my home QTH (the Q-code for station location), in St Neots, I live on a modern housing estate with lots of plasma TVs, BT HomeHub, switched-mode power supplies, energy-saving bulbs, Solar PV energy controllers, etc, etc. All of these give out noise and most of them probably contravene the statutory limits because there is hardly anybody enforcing them. The consequence is that my HF receiver is drowned out by man-made noise. Atmospheric and thermal noise hardly figure.
The S-meter has a logarithmic scale from 0 to 9 and then 10dB increments above. Each point represents a four-fold increase in received signal power (i.e. 6dBm). Thus an S2 signal is four times as powerful as an S1 signal. We record a signal as being (e.g.) S1, or S9 or S9+40.
With no signal being received, only noise, the S-meter on my Icom IC-756Pro II hovers around the S8 mark on an otherwise empty 40m (7.0 – 7.2 MHz) band at home. Whilst I was operating away, with my Yaesu FT-817ND, the equivalent noise was about S1: it was very quiet. In other words, the received man-made noise at home is 28 times as powerful as it is out in the countryside.
Admittedly, this is partly down to the antennas in use. At home I have an inverted-L on 40m; on Nokomis I was using a simple 40m ground plane vertical. That only accounts for maybe 4-6dBm, one S point.
The net effect is that I could hear much fainter stations whilst operating /M than I could when at home. I was working QRP (the Q-Code for low power) and was putting out a maximum of 5W to the antenna. Nevertheless, I could work stations in Ireland and Germany with ease.
The learning point here is to operate /M and /P more often in future. That in turn means I need to spend more time designing an building some simple antennas that I can use effectively on multiple bands whilst away from home. Watch this space.