HF Propagation predictions

For decades, I have pondered what role the weather plays on HF propagation.  I have long since recognized the pattern of rapidly changing atmospheric pressure and simultaneous multi-hop band openings.

Recently, I have reintroduced the Ruuvi sensors into the off-grid ham shack. Their primary role is keeping an eye on the temperature inside the ham shack. Doing so ensures the shack temperature remains above freezing, so the Lithium Iron Phosphate batteries can charge during winter. Since those sensors are inside and outside the ham shack already, why not use the data collected for other projects?

Looking over the sensor data, I wondered if there could be any value having a database of minute by minute weather readings matched with JS8 stations heard and hearing my station. Almost any HF rig could be used to monitor JS8Call frequencies. Collecting and storing the data would be a larger obstacle.

What we would want from that data is historical display of the database based on time of day, temperature, pressure, humidity, callsigns heard and callsigns hearing this station, the grid square of that station, … Over time, a tool could display historic data of stations hearing and being heard, when similar weather conditions exists. For example, my station has heard and been heard by VO1MRK 27 times when the temp was -17c, humidity ~65%, pressure ~1015hPa, during early afternoon. With enough data collected, a tool could start predicting the likelihood of openings to that station. Perhaps a tool could even recommend the more likely stations to try and reach, based on current weather conditions, time of day, and season.
I have not thought this through so be kind.

Long time 50Mhz Operators have known for ages how the band opens up just before or just after a downpour. Predicting band openings and paths would be the holy grail of HF/V/UHF radio. It would also offer a tactical advantage to those who can combine and make use of this data.
Thinking out loud.

Instagram comment

After posting the images from this post on Instagram, this Operator (Fred) pondered the effect extreme cold plays on our antennas. He makes an excellent point. (see image to left).

My response:
The impact of cold temperatures on metal resistance is a relevant phenomenon in materials science. As temperatures decrease, metal resistance usually drops in conductive materials. This is because colder temperatures cause less thermal agitation in the atomic lattice of metals, meaning electrons can flow more freely. This results in a lower resistance. Lower resistance improves conductivity!

Food for thought!

The comment from Fred is relevant. Operators in Northern latitudes often experience HF propagation differently than Operators closer to the equator. The cold must certainly have an effect on coax cable, antenna elements, connectors, … From my perspective, it doesn’t matter if it is the cold reducing resistance on my antenna or its components, or if the weather itself is affecting HF propagation. Anyway, good comment from Fred and probably spot on.

Like I said earlier, I’m just thinking out loud.

Julian oh8stn
YouTube: https://www.youtube.com/@oh8stn
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Blog: https://www.oh8stn.org

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  1. Pure metals typically have a temperature coefficient of resistance of about 0.004 per degree Ceslsius (usually specified at 20C). This effect allows their use as thermometers (as in platinum resistance thermometers for example). The actual change in resistance is quite small – for example operating at 0C instead of 20C would drop resistance by 8% approximately. I guess that this may be significant for an antenna where the radiation resistance is very low – such as a loop perhaps. Unfortunately, the temperature coefficient of resistance for an alloy is often smaller than for the pure metal, so this can reduce the effect by a significant factor.

    I hope that this helps your thinking! 73.

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