Signal reports - mind your noise floor!

Are you a keen user of digital modes?  I certainly am!

In fact, for the past few years, as kids grew up and had early bed times, I was only able to transmit regularly thanks to digital modes and the lack of need to shout down a microphone!

During the years, I've very often noted the sometimes large difference in received and sent 'dB' (signal-to-noise across 2500Hz) reports using, for example, JT65 or JT9 modes.  This large difference can be present both when each station has a simple omnidirectional antenna, and when I am using a good Yagi, with the other using a simple antenna.

The question, then, is why is there this difference?  A little experiment this afternoon showed one of the most significant factors in this phenomenon - electrical noise.

Sorry, terrible conditions on HF here...  [Image: Wikicommons]

I've a simple single experimental PV solar panel that feeds a battery DC lighting system, and also, during good days, feeds a small wattage into the AC mains.  The inverter, like most, produces modest RFI, but is perfectly tolerable, so long as it is producing and not 'hunting' for power on cloudier days, above 80m, which is only ever used here during the night anyway.  When it gets in the way of radio, it can be entirely shut down, day or night.

So, this afternoon, I received an R9 station in western Siberia on 15m.  His report from here was initially -16dB, which is not a bad signal - and he could have been using low power.  But when I turned the inverter off, and the RFI noise floor dropped substantially, the R9 station shot up to a steady -1dB for the next two transmissions.  The other stations jumped in strength also.

Clearly, from this simple test, one reason why I almost never get a signal report better than the one sent is because the vast majority of people are living in settings where their noise floor is significantly higher than mine, here in the electrically-quiet countryside.

So, those folk who get really very excited when I send them a better signal report than their software gave me should really be less gleeful and realise this is only happening in most cases because, sadly, they have a noisy setting that is masking others' signals.