Attenuation By Mould

Lazarus

Lazarus

Retired Moderator
My Satellite Setup
80cm Motorised.
Several small Dishes.
Much else.
My Location
North York Moors
Some years ago I set up for SWMBO an old "Sky Analogue" Mesh (Oh yes) dish with a Monoblock for 13/19E and an offset LNB for 5W.

Never touched it since, but this weekend herself was watching the newly FTA French HD Channels on 5W and complained that the picture was blocky .

It was drizzling outside (Fortunately not inside), but when it stopped the signal became stable.

So, loss of rain margin.

Misalignment or something else? Signals on 13/19E remained full bore, though.

Something else.

Discovered that the LNB feedhorn cap was covered in a substantial layer of mossy green mould.

Cleaned it off and the previously iffy signal reverted to its usual robust parameters.

It seems mould is an Attenuator, with the effect clearly progressive over a number of years, finally getting to the point where extra malign influence like rain pushed it into unacceptable territory.

One of the oddest faults I've come across but also one of the easiest to rectify. A bit of Flash All-Purpose and an old Toothbrush!
 
Interedasting. I had a similar issue with a C120 LNB, where I didn't remove the plastic protective film and the adhesive on the back of it melted and turned opaque, resulting in reduced signal. Removing the film solved the issue.
 
I have had problems in the past with the color green affecting microwave signals.

Years ago (when I was still working as an engineer) I was shop testing a TV microwave link (21 GHz I think) as I reviewed the performance logs I saw a major dip in the test signal at the receiver.

What the heck I said, so looking back I see nothing on the day before or the day after......Hummm, now what caused the drop outs???

I came to light that that day was St. Patrick's day here in the states, and anytime someone walked between the antennas (200 mW test signals only) wearing a green "T" shirt the signals would drop out.

My boss thought I was crazy on this one, when I showed him, I wore a standard white shirt and walked between the antennas, no drop out (not enough to show as a big drop on the test equipment) then changed to a green "T" shirt and low and behold the signals dropped out.

So to be sure it was the color green I used some craft paper of different colors, held them up between the antennas and it looks like the 21 GHz signals did not like the color green in several shades.

So...Green vegetation and microwaves, they don't get along.
 
Very interesting, Terry.

I wonder if one of our Forum boffins might start a Project to quantify the Green Effect .......... I am very happy to donate some sludge!

Other than colour, I did wonder if the water retaining properties of mosses, lichens and other growths might be a factor.


Edit: Dratted speel-chock. Deleted testing and inserted retaining.
 
Last edited:
Lazarus said:
Very interesting, Terry.

I wonder if one of our Forum boffins might start a Project to quantify the Green Effect .......... I am very happy to donate some sludge!

Other than colour, I did wonder if the water testing properties of mosses, lichens and other growths might be a factor.
Click to expand...

Are you suggesting Terry's shirts would be white if it were not for a layer of mould and lichen within the fibres ?

(As for the other 'growth' getting in the way, best not go there)
 
All my "T" shirts are now woodland or desert camo, that way I don't have to worry about the bleach during the wash, and I don't have to try and think as to what type of food or drink was spilled on them.
 
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