Weather and Reception

[mezoo]

Hi Everybody,

I see a strong influence of the weather, particulary rain and overcast conditions, on the reception range.
Is this normal or is my antenna 'getting wet'.

Last month when the weather was perfect (high pressure, sunny and clear skies) my range went up to 120NM.
Now with stormy and rainy weather it is down to almost half that.

I know this problem from SAT-TV reception and do know the high frequency radio waves are absorbed by water (otherwise the microwave oven wouldn't work  ) but just wanted a confirmation that it is normal behaviour and not a hardware problem.

I am using the GNS USB receiver with the supplied antenna elevated as far as possible over my roof window.

Cheers
  Mezoo

[Anmer]

Is the supplied antenna outside?

In 7 years I can't say I've noticed the weather making my range reduce.

[junglejet]

Half the range due to weathe sounds not plausible to me.
A little less may occur, but this sounds like water getting into the way somewhere.

Andy

[Anmer]

I agree Andy.  I don't think the supplied antenna is for outside use?

[mezoo]

Ok. Thanks for the quick reply.

Well the unit is primarily for mobile use and I've read reports of people having it on their car roof when spotting.
It actually has a magnetic base making the car roof an ideal base.

So I assumed that the antenna is suitable for outside use.
During my summer vacation in Ireland I did not see this problem - with the antenna outside as well !
And Irland had plenty of rain during our stay.

Looks like somethings gone wrong.

[Anmer]

Magmounts aren't intended to be left outside for long periods of time.

Over the years I've seen numerous reports of reduced range when using a magmount outside for a long time.

Replacing this one may not be too easy as it has a non-standard connection.

[mezoo]

Looks like it was a false alarm.

In the last weeks I had 'developed' a nice pole extension for the antenna in order to get it as high as possible with the attached cable while still keeping the unit inside. This dramatically increased range and coverage.

However I have not yet figured out how to fix the support base to the roof, so it just stands on the roof by weight alone. (The support is the base of an small garden sun umbrella - about 10kg !)

Not trusting this construction with the higher winds in the last few days I replaced this with a shorter pole.
This lower antenna elevation dramatically cut the range.

Today with calm weather the long pole is out again and range is as usual.

But taking up your comments I have taped all connections to keep out any water, maybe that helps as well.
I will also remove the magnetic base.

Thanks for your comments.
From my experience with SAT TV reception I had expected a larger influence of rain and moisture in the atmosphere on the signals.

[OH7HJ]

Hi Everybody,

I see a strong influence of the weather, particulary rain and overcast conditions, on the reception range.
Is this normal or is my antenna 'getting wet'.

Last month when the weather was perfect (high pressure, sunny and clear skies) my range went up to 120NM.
Now with stormy and rainy weather it is down to almost half that.

I know this problem from SAT-TV reception and do know the high frequency radio waves are absorbed by water (otherwise the microwave oven wouldn't work  ) but just wanted a confirmation that it is normal behaviour and not a hardware problem.

I am using the GNS USB receiver with the supplied antenna elevated as far as possible over my roof window.

Cheers
  Mezoo

Hi Mezoo,

In what kind of surrounding you live? Plains, sea, suburbs or forests around?

Yes, these GHz waves really are absorbed by wet trees. I have observed weather attenuation in these deep northern forests for decades during my ham radio activities. It always goes the same way: When forests get wet, UHF signal levels and reception ranges dramatically decrease. Even by half.

That is true to any close to GHz range signals, not just these ADS-B. On still higher SHF bands like the SAT TV even atmospheric humidity decreases signal levels as you have found out. My SAT reception freezes due to thick rain clouds, too.

As soon as the weather dries the woods again, the ranges again increase. Also when the weather freezes in winter, my ADS-B reception range increases quite like with dry weather. A 'dry' frozen snow and ice does no absorb RF.

However, as soon as ther weather warms up and the forests start to melt, the reception range again dramatically decreases! That is why cold freezing winter is usually the best weather up here for long range UHF reception.

So the ADS-B range of reception work like a barometer or weather station. Read the humidity and temperature of surrounding forests from the ADS-B range! 

In plain or urban environment the humidity of surrounding environment may have very little effect. The weather related UHF signal loss is characteristic for QTH's surrounded by natural vegetation or cultivation.


- Juha -

Pics below: A moderate wet October max reception range of 75 nm compared to max range 140 nm in dry freezing winter weather in November.

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[Smokey]

Question if I may ...

whats the effect of silicone spray's & water repellent sprays etc on/inside RF connectors at this freq ?

will they have adverse effects ?

[OH7HJ]

Question if I may ...

whats the effect of silicone spray's & water repellent sprays etc on/inside RF connectors at this freq ?

will they have adverse effects ?

Hi Smokey,

Any dielectric insulator, solid or liquid, between coax center lead and braid absorbs RF field - meaning they attenuate. The dielectric losses increase with frequency. That is why foam insulated coaxes are preferred for long feeds - say more than 10 ... 20 meters -  on 1 GHz ABDS-B band. 

However, a mere connector is a very short section of coaxial feed line, so you do not need to worry about spraying it. The dielectric loss in a connector is so minute that it can not be noticed.

It is quite another matter if a long length of coax gets soaked from between braid and center insulator. Water leaking in is of course the usual dielectric to cause coax soaking. A few meters of wet coax may increase attenuation on this 1GHz band by several decibels. However, soaked coaxes may still perform quite well on lower freqs like on HF and low VHF bands, because dielectric losses are marginal down there.


- Juha -

[mezoo]

Hi Juha,

sorry I did not see your original reply to my post.
Thanks for confirming my suspicion.

I live on the outskirts of a large city - near EDLW.
To the north are the german lowlands, which on a good day gives me a range of up  to 220Nm.
Then I can see the planes flying in from Scandinavia while they are still over the Baltic sea near the border to Denmark.
On a wet and foggy day like today I get about 180Nm range.

I also get the impression that the number of planes for which the position data is received seems to drop off.
The total number of planes detected seems to be the same, but during wet weather position data is only received for about half the planes is received.

To the west I am blocked by the local terrain, houses and trees.
To the east and south there is a hilly wooded area which reduces the range considerably, About 80Nm.
Unfortunately that is also the approach to EDLW so I only see the planes just before landing.

Attached is my cumulative plot from SBSPlotter.

I am still using the mobile rod antenna and the antenna cable as originaly supplied with my GNS.
But I am looking into getting an antenna more suitable to continous outside use.
Any recommendations would be most welcome.

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[viking9]

An area of high atmospheric pressure (1028 hPa) is moving towards the British Isles from the south west bringing with it some mild to strong tropospheric ducting and associated increase in VHF/UHF/Microwave propagation over today and tomorrow.

http://www.dxinfocentre.com/tropo_nwe.html

[OH7HJ]

Hi Mezoo, 

Yes, your plot shows finely your clear reception area to northwest and the shaded area to southwest!

My own practical experiments building and comparing 1 ... 16 element 1090 MHz aerials would suggest that aerial height appears more important than its gain in obstructed surrounding like residential area, hills or forest. Aerial gain sure increases distance of reception on 1090 MHz but not always as much as raising it above surrounding terrain and obstacles.

If feed line length extends to about 20 m or so when raising aerial, one may of course need to purchase expensive low loss foam filled coaxial for it.


Hi Viking9,

Weather phenomena like tropo scatter do really extend 1090 MHz range, too!

If the high pressure is associated with inversion, meaning a layer of air with higher humidity and temperature than the air below near surface, we may be lucky to get an inversion tropo scatter which bends VHF (30 - 300 MHz) and UHF (300 MHz - 3 GHz) and even SHF (3 GHz - 30 GHz) waves back down beyond radio horizon in the boundary or the dry low air layer and the high humid air layer.

These inversion tropo scatters are usually associated with calm and clear autumn and winter days. A visible sign of inversion layer are smokes from high chimneys suddenly bending on their way up. The smoke trail bends when it hits the inversion layer.


Pics below: First pic is an example of my 1090 MHz reception range extended to west, south and north by a humid air inversion layer. The humid air layer was told in this case to have drifted from Lake Ladoga to over Finland. The inversion layer did not reach east so my reception range is not affected there. I confirmed the scatter as a tropo inversion by extended range of reception on ham 2 m VHF band, too.

Lower pic shows the reception range derived back to usual after wind blew the inversion layer away.


- Juha -


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[viking9]

Hi Viking9,

Weather phenomena like tropo scatter do really extend 1090 MHz range, too!

- Juha -

Yes, I know. That's why I included MICROWAVE (1GHz to 300GHz) and posted here