FlightAware Discussions

Tropospheric Openings and impact on 1090Mhz DX

Another newbie observation, but thought I would share the details because I’m keen to learn.
I can appreciate that on fine days and weekends I see a lot of extra light aircraft coming out to play and adding to my daily totals. However what I found interesting having had a look at some nearby sites, was that we all share a peak around 20 Jan here in UK.
I correlated that with data from my weather station and sure enough we had the highest pressure reading (around 1048 mbar at my QTH) that I have seen in long time!
Since I’ve only been involved with receiving ADS-B for as little as a month I don’t have any feel for the impact on DX at 1090 Mhz.
In general do other folks in the community observe correlations with tropospheric openings (such as ducting) which often helps amateur radio contacts at VHF frequencies?
Here’s my observed correlation to the building pressure gradient that we experienced in UK earlier in the month…


It’s not clear from my data if this is just coincidence or if watching the pressure reading in future would be a useful predictor for better totals. I’m still going through a period of tuning gain on my own receiving site but I’m coming to realise that it’s not a simple matter :slight_smile:

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ADS-B is definitely affected by tropo conditions. Have a look at this previous thread about the subject: Nice bit of tropo over the UK and Europe today

Yup, I posted on the 20th January in thread that @caius has linked.

Thanks @caius , @keithma , great to hear that I can expect some openings from time to time due to Tropo.

Is that cool!

This is another sentence so the bot let’s me reply.

Any clear sunny day followed by a colder foggy night and where the pressure is above 1030 mb and falling is likely to see long distance ducting. Best reception is often across the trailing edge of the high pressure across the isobars to an area of similar pressure on the other side of the high.

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Thanks that’s really useful information.
In the days of analogue TV it was always very evident when a lift was on (patterns on picture!), not so obvious with DTV, which tends to be 100% or 0%
However I am pleased with the reliability of the pressure correlation. From here I saw three main peaks in January, all of which resulted in DX on 1090Mhz. The opening on 20th was particularly impressive (as witnessed by comments and observations on the linked thread) and it did coincide with that unusually high 1040+ mbar pressure reading over UK.


Watching that barometer in future may pay dividends.

Longest distances from IO90 on 144MHz … IL28 to the south and KN09 to the east - on tropo with 10 Watts. This was back in the 1980s or 1990s from 6m asl in Dorset.

Wow fantastic distances. Probably same period, I was into RTTY on 144 and a friend sat in a field on the Mendips managed to chat to me in Wiltshire on literally milliwatts of power. I also remember Italian TV on 50Mhz being endstop at times, but that may have been related to Solar conditions rather than Tropo - can’t remember what year exactly.
Quite amazing what 10 watts will do when conditions are “right” :slight_smile: 1090 Mhz is new to me so I find it all quite interesting.

The opening earlier in the month was much more impressive - I was seeing helicopters at 300ft AGL in Denmark!

During that same lift, I heard a familiar voice through my local 70cms repeater and it was a friend I’d not spoken to in quite a few years. I’m right on the east coast of Essex, he was driving around Wales! On the input, he was a solid S2-S3 so easily workable simplex.

In 2010 I worked two Russians in KO85 at around 1500 miles on 2m and I think that’s my best DX on 2m via tropo. I’d was using around 90W with a 9 element Vargarda at about 25ft AGL.

We used to use RTTY for local chat using 2m FM (with extra fans on the radios for cooling), I started off with a Creed 444 teleprinter and then got software for my Acorn Atom which I used with a hombrew terminal unit.

Ahh, nostalgia. It ain’t what it used to be :smiley: :smiley:

ADS-B/Mode-S on 1090 MHz is transmitted at up to 500 W actually.
But you probably were referring to the other radio stuff?

Yes we were just referring to 2-meter band and generally reminiscing :wink:
But I hadn’t realised up to 500 W was used at 1090 Mhz. Thanks.

The Italian TV reception on 50 MHz would have been via Sporadic E, most likely sometime between late May and mid August or, less likely, late December to early January.

Likewise, exceptional distances in June and July can be worked for short periods of time on several occasions on 144 MHz via the same mechanism. In the US, Es has also been observed on the 220 MHz band on a few rare occasions. That’s about the limit.

Troposperic ducting is more of a late summer, autumn, early winter thing as it is atmosperic rather than ionosphic. On the other hand, there is speculation that Es has connections with both meteor showers and thunderstorms.

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An interesting aspect of anomalous propagation is that it tends to be within a layer of the atmosphere, and often not very high. That would explain seeing helicopters at 300 ft across a distance but not seeing a big jump in range for, e.g., aircraft at much higher altitudes.

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I didn’t know that, interesting, that behaviour has indeed been seen.