HF radio performance loss due to EMI-RFI and noise in and around the station environment is often a major issue that could almost cripple the communication capability. This is especially true during conditions of low SSN, the way it prevails during the ebbing part of the Solar Cycle. Many amateur radio operators do not realize the real consequences and the utter magnitude of loss in their radio station’s performance. More often than not, we have heard statements like – The HF bands are now dead at low SSN, the only viable way is to work HF using FT8, SSB radiotelephony is hardly possible during low SSN conditions, I think I need to invest in a linear HF power amplifier, etc, etc… – We have heard all this far too often. However, it is not necessarily the whole truth.

We all agree that during low SSN conditions, negotiating the HF radio bands become more difficult and stringent in comparison to what happens during the better part of the Solar Cycle. When the going is good during moderate to high SSN, a mediocre quality or even a rather poor quality ham radio station may allow one to work around the whole world, however, the scenario is quite different during low SSN. The received signals are weaker in strength. Therefore we can no more afford to get away with a noisy radio station setup. The crux of the matter is that we need to optimally reduce the HF band receiver noise floor that exists on our transceiver… If we do this, we would discover that the bands are not really dead.

I have written several articles about this earlier. I suggest that you also read those articles to attain absolute clarity on the subject and also get to know about some important tweaks that you might need to do on your station setup for overall performance improvement. I will provide links to these articles further down. Meanwhile, let us see how badly could local area noise literally render an HF ham radio station practically deaf unless we take care to minimize the receiver noise floor levels.






HF Radio station Noise Floor minimization is a game changer
Although there are various other factors that contribute to the quality of the ham radio station’s performance capabilities, it is the unoptimized noise floor level that is most destructive and can render the HF radio station practically useless during low SSN conditions. I am sure that many of our readers might still be unable to fathom the extent of damage to communication that one’s receiver noise floor could do. As they say, a picture is perhaps worth a thousand words, Therefore, I will try to drive home my point with an emphasis on graphical presentations.

Further down the article, I have presented computed map coverage of propagation possibilities that would exist at different levels of noise floor at the receiver. These propagation coverage maps have been produced w.r.t. six different ham radio station locations from around the world. These locations are spread over various continents to provide a sufficient understanding of what really happens.

The above-cited HF propagation map renditions were made for locations based in the USA, Europe, India, Africa, Australia, and South America. These maps are all based on the actual SSN and propagation conditions that were prevailing on the 3^rd January 2022. The projections were done for DX openings on the 15m band on that day, during the optimum time of the day.

All station parameters were kept identical. The renditions were done with identical 15m Dipole antennas deployed at 45 feet above ground level (AGL). All other radio station parameters were kept identical. The transmitter power levels were pegged at 100W PEP for every station. The receivers had identical sensitivity and were set to identical filter bandwidths.



If one lives in a rural environment with a well-setup, low noise antenna system, and a low low CMC transmission line; it is enviable. The rest of us who stay in urban areas may not be so lucky, yet a good station setup will allow enough DX… However, those who live in cities and also have a mediocre/poor station setup with 15m band noise floor at S5 level or higher are classic examples of those destined for total disaster… Such people need to seriously introspect, do the right things needed to reduce the HF receiver noise floors.




HF propagation prospects at various noise floor conditions
Now, let us see how all that we have discussed so far translates into the actual HF radio propagation prospects for us. Remember, all ham radio station setup parameters have been kept identical in all scenarios presented below… The only factor that changes is the noise floor level at your receiver.

The HF radio propagation prospects for all the six cited global locations have been plotted on maps for an easy perspective. Each of the propagation map projections consists of a set of 3 map slides. One each representing the rural (-160 dBW/Hz), urban (-145 dBW/Hz), and a poorly setup HI-QRM urban station (-128 dBW/Hz) noise floor levels. The three scenarios for each location are projected as a continuous loop slide show. This will provide a quick pictorial insight into how disastrous the presence of excessive noise can be on an HF radio station’s performance… By looking at the slide-show map projections, one would definitely understand why is it that many amateur radio stations with unduly elevated noise floor levels are unable to find HF DX propagation openings during a low SSN phase… Check it out!

In all map projections below, red-orange-colored regions represent good communication prospects, yellow-green-colors represent marginal prospects, and cyan-blue-colors mean no communication prospects whatsoever.

HF propagation at USA under various local noise levels

The radio station location for the purpose of this projection has been selected in Florida, USA. The rural noise level station has a ball with remarkable openings even during low SSN. The urban station with a good setup also fairs pretty well. However, look at the scenario where the station has a poor local noise performance… The results are disastrous with little or no ability to work anything substantial on HF radio bands.

HF propagation at Europe under various local noise levels

The radio station location for the purpose of this projection has been selected at a location in central Germany... The interpretation of the HF propagation projections under the three noise level conditions is the same as in the scenario for USA.

HF propagation at India under various local noise levels

The radio station location for the purpose of this projection has been selected at New Delhi, India... The interpretation of the HF propagation projections under the three noise level conditions is the same as in the scenario for USA.

HF propagation at Africa under various local noise levels

The radio station location for the purpose of this projection has been selected at a location in Botswana, Africa... The interpretation of the HF propagation projections under the three noise level conditions is the same as in the scenario for USA.

HF propagation at Australia under various local noise levels

The radio station location for the purpose of this projection has been selected at a location in central Australia... The interpretation of the HF propagation projections under the three noise level conditions is the same as in the scenario for USA.

HF propagation at South America under various local noise levels

The radio station location for the purpose of this projection has been selected at a location in central South America... The interpretation of the HF propagation projections under the three noise level conditions is the same as in the scenario for USA.




A wrap-up of this discussion
What we have observed above leads us to a clear conclusion. Irrespective of where your radio station might be located, it is the minimization of HF noise floor level at your transceiver that is of utmost importance. Failure to effectively address unduly high noise levels at the receiver would invariably lead to absolute catastrophe... You will then be left with no other option but to fall back on ultra-weak signal modes like FT8. You will be bereft of the real joy of work modes like SSB radiotelephony, etc... So, pay attention to any noise problems that you might have at your end and set it right! ... Unless you address the noise problems, it would be futile to go on a wild goose chase hunting for better transceivers or bigger antennas.