Odd satellite reception from behind glass

timo_w2s

Last night I was testing a dish setup on a balcony which has panes of glass to close it off and turn it in a mini-conservatory. Location Helsinki, southern Finland, clear skies.

I was a little surprised by the results and wondered if anyone else has experienced this.

The dish was looking at quite a steep angle through the glass for the satellites at 28.2 to 13 degrees east. Using a 75cm dish on all these satellites I was getting decent strong signals from all horizontally polarised signals through the glass (quality of about 70-80% on a TM1500). With the glass removed signal quality increased by about 10%.

However, this is where it gets weird. I was getting no usable signals at all on any vertical transponders through the glass. The receiver would not lock on to anything no matter how I tried to fine tune the dish or skew the LNB. As soon as I removed the glass, signal jumps to 80%+ quality like on the horizontal transponders.

The glass panels can be removed in sections. What I found even stranger was that if I only half covered the dish with glass I'd loose all reception from horizontal as well. I would have thought V channels would start coming in a bit and it wouldn't have effected the H channels, but no, I get nothing.

So to sum up...

- Through glass I could get horizontal signals only with minimal loss in quality.
- With no glass I can get both H and V signals as normal
- Half covered by glass I get nothing at all, just as if I was standing in front of the dish blocking the signal.

When I tried picking up Sirius and Thor I was getting similar things through glass except I could just about get a weak lockable signal on the V channels of around 30% and near full again on the H channels.

I guess this is probably down to the stronger signals of these satellites in my area and perhaps helped a little by a more favourable angle of the dish looking through the glass (the balcony faces west so in Helsinki Astra 2 is almost due south and the rest are west of south).

So it seems like the glass is polarised. Presumably for sunlight but why would it also effect radio waves? I kind of assumed I would either just get no signal or some signal but not with such a huge difference between polarisations.

I suspect this might be a silly question, but is there any way to get vertical channels through the glass without removing it? Or will my satellite viewing be restricted to horizontally polarised signals only during bad weather (ie most of winter!)?

Tivù

I always enjoy reading about this kind of thing.

There are as many opinions about the relevant factors and constraints as there are holders of opinions.

I've found in the past that making even relatively qualified and sensible input is often trumped and defied by the practical experiences of others, so I'll just go into "sponge" mode on this Thread

Key Buzzwords:

Manufacturing Process
Polarisation
Permeability
Refraction
Diffraction
Reflection
Permittivity
Attenuation
Scattering


...................... and many others!

timo_w2s

Thanks, they all sound like good reasons!

I've now been looking at a LX2000 Pipe Antenna as it only has a 16cm diameter which I could poke through a small gap in the glass to get the verticals for one satellite but they aren't cheap and I've read they aren't particularly good in weaker signal areas like Finland (I'm thinking for Astra 1 or Astra 2 northern beam only).

Vipersan

...absolutely fascinating ..
..and fwiw I agree this does indeed sound like the glass is acting as a polarization filter ..
..not unlike the old polaroid sunglasses ..
When you think about it ..
..light and radio waves are literally just seperate bands within the same electromagnetic spectrum ...so no reason why treated glass couldn't behave in this way ..
Chances are if you removed a pane and rotated through 90 degrees ...the missing polarity signals would appear ..and the current ones vanish ..
rgds
VS

Topper

I agree with Gordon on this matter, there are many reasons why this could be happening, you have to remember that a large proportion of window glass that is used in double glazing is treated to allow heat to pass through in one direction and reflect it back from the other, indeed IIRC this was invented for cold countries such as Finland. The characteristics of these coatings and their effect upon signal attenuation is wide and varied dependant upon manufacturer, type and correct manufacture and installation. Removing the glass unit and reversing it will give more than likely give a different result, of course they may have been installed incorrectly and all the heat is going out , the permutations are endless. I would certainly have thought that 75cm was too small for sufficient reception through glass from your location.

War does not determine who is right, it determines who is left!

Formerly toppervte33h
whose six pack has turned into a keg

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BombedOne

Plain, cheap glasses (ones we poor countries use), affect both polarities in same way...

timo_w2s

I thought the same but as I'm 22 floors up and it's a long way down I didn't fancy trying to remove the heavy sheets of glass off the tracking to test the theory.... It's scary enough just looking through the glass without hanging on outside trying to unscrew it.

I think you are right, but it was just a very cheap and nasty spare dish I had lying about that was useful for testing. Although to be honest I'm not sure I can physically fit anything much bigger than an 85-90cm anyway. I really wanted an Inverto MultiConnect multi-LNB system on a SatPlus 85cm Transparent Dish but now I'm wondering if this will cause problems especially with some of the outer LNBs.

I've already resigned to the fact that I'll only get Astra 2 north beam but I can get Astra 1 (inc Polish beam) on a 45cm dish here (with no glass!). Hotbird is a bit weaker.

That's what I was expecting here too!