Category: Southern North Sea Studies

What this image does not show is how much the wind has increased since the pre-dawn calm. The reason for the wind increase is implied from the image though as the storm system over France starts to influence weather in south-east England. To minimise wind loading I have set the dish to point at F5ZTR on 3cm and can see a weak but continuous signal from this beacon.

At 191km distant it is close to the theoretical trans-horizon limit from here.

With a High pressure area established over southern Norway fresh Eastely winds are expected to dominate the weather today. Just now at around sunrise the air is calm and clear of cloud but filled with birdsong (blackbirds and sparrows mainly).

The 3cm beacon looks quiet. On the direct heading heading F5ZTR is visible in the waterfall and amplitude appears relatively constant.

GB3PKT whilst only about -15dBjt on the direct heading is considerable stronger (-13dBjt) on the heading for PI7ALK. This is anomalous as I usually receive the Essex beacon via a faint reflection (-19dBjt).

This beacon arrives from many azimuth angles when there is “weather” so I will note the signal and look around.

In the breeze it is a little difficult to keep the dish pointing to within 0.1 deg using the existing mounting arrangement. To reduce the noise introduced I average the spectrum over 10 seconds. Processing the signal is a topic I need to investigate and will return to later.

PI7ALK is a weak scattered signal (about 50Hz wide). Best description is that it is a smudge on the waterfall, amplitude and phase varying signficantly so that no sharply defined carrier can be seen.

This is the usual signal when the North Sea wave height is about 2m, and clear air (no cloud) conditions dominate. Troposcatter.

Varying the elevation angle shows that the signal peaks pointing at the horizon.

PI7ALK has drifted in frequency a little overnight to 10368.898.9 suggesting a cold night in Alkmaar.

In this quick bandscan no other signals can be spotted, apart from short burts on 10368.840 and 10368.972 probably aircraft scatter. The latter is likely to be DB0MU as I receive it frequently the ALK dish heading.

No signals are to be found with the dish pointing towards DB0GHZ. Even GB3PKT has disappeared. So all-in-all a few quiet start to the day.

It is no surprise that there is a sparsity of signals this morning as all the indications are that the wave height across most of the southern North Sea is well above 1.5m. Remember that evaporation ducts at 10GHz are unsustainable where wave heights are above about 1.6m. This seems to be the case this morning as indicated by this chart

From a propagation perspective a bit of a strange day.

All the usual beacons PE9GHZ, ON0VHF, PI7RTD, PI7ALK and ON0GHZ have been audible all day via scatter from any beam heading from about 0 deg to 135 deg with very little amplitude change.

Around midday utc I carried a swift investigation to understand if elevation mattered at all. PE9GHZ and PI7ALK proved most stubborn, only disappearing when elevation reached 20 deg. The others disappeared at around 12 deg.

All this has been due to a cloud mass that is sitting over the southern North Sea. It was this same cloud mass that caused the thunderstorms earlier in the day and ground to a halt as it came up against the developing High pressure system off the coast of Norway.

This system is expected to slip further south on Sunday.

Of partcular note though, apart from not having the pigeon return to sit on the feed, is that DB0GHZ has been audible as well. Looking closely at the signal it is clear it is arriving here via weather scatter. That is it is affected by the cloud mass is not surprising and I expect it is an occasion where ducting and weather scatter modes combine.

It will be intersting to see what happens as the cloud dissipates.

Wave height has reduced during the day and is currently about 1m so evaporation ducting enters the equation even up to Heligoland.

The strong cold currents from the north are mixing with warm English Channel currents in the Dover Straits, which maybe the cause of the fog.

Following the thunderstorm epic drama focus returns to the original purpose of these notes – Propagation over the North Sea.

With the storm cell location still firmly established across the southern North Sea the noise level on 3cm has increased by about 1dB (-128dBm/2.7kHz compared to -129dBm/2.7kHz normally).

With the dish pointing directly to PI7ALK a band scan shows good readable signals from PE9GHZ, GB3SEE, PI7RTD and PI7ALK. ON0GHZ is lightly weaker than the rest.

As there is heavy rain it is likely all these signals are arriving via rain scatter rather than the anticipated lower level scatter and ducting modes.

Evaporation ducting is not expected to be noticeable today as the latest information on North Sea sea state indicates wave heights of at least 1.5m away from the coastal boundaries. As noted before anything abouve 1m reduces the strength of signals from the evaporation duct and calculation have shown that the duct breaks up with wave height of 1.6m or higher. We are close to that limit today.

It looks very much as if weather effects will dominate today