Re: Tropo


Nicholas Shaxted
 

There are multiple contributing factors that have made for some interesting propagation conditions this autumn.

The main highlights from an amateur radio perspective is that a relatively stable High pressure region formed consistently of multiple High pressure systems. Their dissipation allowing elevated temperature inversions to occur and also existed opportunity underneath for an almost contiguous surface duct to form.

 

If you look at the appropriate data (Skew-T Charts) across a number of cities across Europe you will quickly see that these temperature inversions were at 950 (~500m asl)  and 750hPa (~2500m asl). The low level inversion has been present from Manchester to Warsaw and from Stockholm to Stuttgart and provided microwavers with decent opportunities for contacts. The higher level one has been a little patchier and from the data I have collected seems more confined more to northern areas of Europe (Copenhagen and northern Germany) and thus probably confused many VHFers

 

I have said on this reflector before that skewed propagation are the result of refraction through an air mass body. This mass will be subject to changes in temperature, humidity, local pressure and wind which will contribute to a swirling (slow moving) mixing blob with variable refraction properties. The speed of mixing takes place over hours and can produce strong localised refraction in any plane (it is a 3D body). At microwave frequencies it is not unusual to see angles of arrival varying a number of degrees in azimuth over a short time.

 

Local signals here tended to remain anchored to the horizon (0 deg) elevation) but significant  (3dB or so) improvement to some long haul signals were measured (SK1SHH at 1306km, OZ1UHF at 915km) with the dish elevated by between 0.2 – 0.4 degrees.

 

Nick – g4ogi

 

 

 

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> On Behalf Of SAM JEWELL via groups.io
Sent: 22 September 2020 16:10
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Tropo

 

Although we are probably agreed it was predominantly an elevated duct for the real DX, the number and strength of Dutch stations on 2 and 70 (maybe a few on 23cm but activity is lower) seems to indicate a low level surface duct was also present.

Reflections from single ships and builds are not likely to result in much of a reflection, but we are talking about hundreds, if not thousands of significant buildings/ structures along the coast and within the common volume beamwidth of the antennas.

On 2m there was some evidence of multipath on some of the stronger FT8 signals in the UK, who were, presumably, beaming east towards the continent.

I have, over the years, worked a number of northern England and Scotland stations by beaming eastish from here in Suffolk. This mainly on 23cm, back when there was more activity. Skew paths on 10GHz are quite common and again it may be reflection or refraction. The Galloper and Great Gabbard wind farms are the biggest contributors here.

I might add that the Belgian radar on 23cm was really strong the last few days. The noise blanker really was unable to take it out on any setting. Not just every eight seconds of rotation, but continuous, as it rotated and reflected from every object it illuminated!

 

73 de Sam, G4DDK

 

 

 






------ Original Message ------
From: "Marcus Walden" <marcus.g0ijz@...>
To: UKMicrowaves@groups.io
Sent: Tuesday, 22 Sep, 20 At 14:57
Subject: Re: [UKMicrowaves] Tropo

I don't think there will be any tropospheric propagation via 'vertical incidence'. However, we are interested in the vertical refractive index profile because that provides an indication of whether or not ducting is likely. Is there a mix-up in terminology in an earlier posting?

Looking at radiosonde data for Schleswig (Northern Germany for Sunday 20 September at 1200 UTC and Monday 21 September at 0000 UTC, there is evidence of a very strong elevated duct - sufficiently strong to support VHF and UHF. Was there tropo activity on 2 m and 70 cm this weekend? I don't know because I'm HF QRP and currently without an antenna.

The elevated duct and inland stations might be an indication that the off-great-circle paths are not caused by reflections from ships. Hills/mountains?

With HF propagation, there can be horizontal gradients in the electron density in the ionosphere, which results in bearings that are not great-circle. Could a similar effect be happening within the troposphere? In other words, there is refraction in the horizontal plane (or at least not vertical), as well as in the vertical plane.

Perhaps anomalous bearings could be collected from multiple stations to see if there is a common characteristic or focal point on a map? What about weather conditions in this region, if one is identified?

73 Marcus G0IJZ

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