5G Network interference:

[armadillo_115]

Interesting question.

Isn't it reciprocal for receive and for blocking?

I'm guessing mesh size has to be LESS than 1/2 the wavelength to begin ANY shielding. The lesser the better or some signal may still get through. Especially for stronger signal levels.

As an example:: Take an old C Band dish that has mesh too large for adequate Ku frequencies. It will STILL receive some Ku signal. And the stronger the signal, the more will be received.

Waiting to hear the correct answer.

 

[primestar31]

3.8GHz is about 8cm wavelength so do the holes in the mesh just need to be less than the wavelength of the signals?

That's EXACTLY correct! IF the holes are smaller than the wavelength, that frequency and below would be blocked or reflected from going through. How much so, depends on the hole size compared to wavelength.

 

[N6BY]

What's the technical theory on an RF fence? 3.8GHz is about 8cm wavelength so do the holes in the mesh just need to be less than the wavelength of the signals? Does anyone understand the science behind it?

SE dB = 20*Log10(λ/(2L))

Shielding effectiveness (in dB) is calculated using the above formula where λ is the wavelength and L is the size of the largest hole.

Assuming a mesh size of 1" (or 2.54cm) for chicken wire and a 3.8 GHz signal with a wavelength of 8 cm, the shielding effectiveness works out to 3.9 dB which would not block out enough 5G.

But 1/16" mesh would yield 28 dB of attenuation. Probably enough.

Chicken wire
20*log10(8/(2*2.54)) = 3.9 dB

1/16" mesh
20*log10(8/(2*0.15875)) = 28.0 dB

But how would you design the RF fence? What geometric shape would it be and how many square feet of mesh would it take?

 

[armadillo_115]

While searching fruitlessly for an answer I found something interesting on Wikipedia.

Concerning reception on parabolic:
For a MESH dish to equal a SOLID metal dish, the mesh has to be smaller than 1/10 wavelength. Assuming both dishes are perfectly parabolic, etc etc.

 

[Tower Guy]

SE dB = 20*Log10(λ/(2L))

What geometric shape would it be and how many square feet of mesh would it take?

It would look like a small backstop for a baseball diamond. The 1/10 wavelength rule is true, so 1/4” hardware cloth would be the material of choice. The size would be slightly larger than the area of your dish and feed horn.

 

[N6BY]

It would look like a small backstop for a baseball diamond. The 1/10 wavelength rule is true, so 1/4” hardware cloth would be the material of choice. The size would be slightly larger than the area of your dish and feed horn.

Would it be in front of the dish or behind it? A drawing might help.

 

[primestar31]

Would it be in front of the dish or behind it? A drawing might help.

It would have to be around the rim. Like the outer rim of a steel-walled swimming pool.

Or IF you know exactly what direction the 5G is coming in from, you might be able to put it up in the air like a billboard, just to block that signal direction. But in a way that wouldn't block the satellite signal.

 

[Tower Guy]

Would it be in front of the dish or behind it? A drawing might help.

It goes between the dish and the 5 G cell tower.

 

[N6BY]

It goes between the dish and the 5 G cell tower.

Of course, but 5G is all over the place here. I like primestar31's idea. I already have some wire mesh but I am not sure of the best way to form it into a cylinder that would attach to the rim of the dish.

 

[primestar31]

Of course, but 5G is all over the place here. I like primestar31's idea. I already have some wire mesh but I am not sure of the best way to form it into a cylinder that would attach to the rim of the dish.

Cut it as tall as you think you'd like or need, and make sure it's long enough to make it all around the entire rim, and maybe a little overlap. Buy some BIG head sheet metal screws. Start at the bottom edge of the dish, whereever is handy. Put in the first screw or two, and slowly make your way around the dish rim, screwing in screws to hold it. When you finally get all the way around, overlap a little bit and use picture hanging wire to stitch it up that entire edge...

If it's not as stiff as it should be, you might have to use some metal weatherstripping (or reasonable facsimile thereof) for the screws to go through first, then the mesh, then into the dish rim.

 

[Titanium]

I would only affix shielding to the rim of a fixed dish, when you know the signal is coming in from the side. In my opinion, it is a waste of money and time to install on the rim of a motorized reflector.

I doubt that the 5G interference is coming in from all over the place. 5g 3ghz mid band interference is likely to be arriving from one direction as the geographical coverage is cellular and typically used for fixed service such as home internet. Determine where the interfering signal is coming from and place the rf shield beween the source and the dish. The signal may be reflecting off of the dish surface, a single or multi bounce reflection from a nearby surface or entering directly into the feed.

You don't always need to construct a big rf shield to reject interference. Example: I once affixed a 6" square piece of hardware cloth to the outer ring of the scalar to prevent a terrestrial signal from entering the feed when the motorized dish was pointed in one direction. Yes, I could have built a 10 foot or larger mesh rf wall to shield the entire dish, but watching the spectrum analyzer as the dish rotated, showed the interference was only a problem for two satellites. Since I had already identified the interference source, it was as simple as holding a baking sheet in several positions to find the best spot to install a shield, used some aluminum foil to test then drilled riveted on the hardware cloth shield.

Maybe it is time to plant a living RF hedge or install a "privacy fence" to increase the "WAF" = Wife Approval Factor of the BUD and also RF shield the dish. 3ghz signals are easily attenuated. Many satellite dish owners can relate to c-band signal attenuation and loosing reception of their favorite satellite during the summer months when the leaf cover arrives.

 

[N6BY]

Cut it as tall as you think you'd like or need, and make sure it's long enough to make it all around the entire rim, and maybe a little overlap. Buy some BIG head sheet metal screws. Start at the bottom edge of the dish, whereever is handy. Put in the first screw or two, and slowly make your way around the dish rim, screwing in screws to hold it. When you finally get all the way around, overlap a little bit and use picture hanging wire to stitch it up that entire edge...

If it's not as stiff as it should be, you might have to use some metal weatherstripping (or reasonable facsimile thereof) for the screws to go through first, then the mesh, then into the dish rim.

I have 34' of 3 foot wide 1/16" wire mesh, which is a little more than enough to encircle my 10' Unimesh dish rim. But the mesh is not even close to being stiff enough to stand on its own. I would need to screw support arms onto the dish rim and wrap the mesh around them.

I bought the mesh a few years ago for a LOT less than what it costs now. I cannot believe how expensive it is. Because of the cost, if I didn't already have the mesh I would not try this experiment. And it is just an experiment since I already have a Titnium C138 LBNF which works fine. (Will do the testing using an older LNBF without filtering, of course).

... As for where the 5G is coming from: I took a C-Band LNBF (without a dish) and hooked it up to my TBS6983 satellite tuner card and did some testing with the mouth of the LNBF pointing in various directions. I did spectrum scans every 45 degrees and saw 5G signal spikes on all of them.

 

[Titanium]

I have 34' of 3 foot wide 1/16" wire mesh, which is a little more than enough to encircle my 10' Unimesh dish rim. But the mesh is not even close to being stiff enough to stand on its own. I would need to screw support arms onto the dish rim and wrap the mesh around them.

I bought the mesh a few years ago for a LOT less than what it costs now. I cannot believe how expensive it is. Because of the cost, if I didn't already have the mesh I would not try this experiment. And it is just an experiment since I already have a Titnium C138 LBNF which works fine. (Will do the testing using an older LNBF without filtering, of course).

... As for where the 5G is coming from: I took a C-Band LNBF (without a dish) and hooked it up to my TBS6983 satellite tuner card and did some testing with the mouth of the LNBF pointing in various directions. I did spectrum scans every 45 degrees and saw 5G signal spikes on all of them.

An open feedhorn without the focusing provided by the parabola has a very wide beamwidth. Like using a machete instead of a scapel for a surgery. It will provide a general idea of the signal presence and general direction. I would expect to see spikes of varied amplitudes when using an open feedhorn, strong signals from direct line of path and weaker from reflected. The weaker signals are increasing the noise floor, but are not likely to a level to swamp the lnb conversion or tuner.

 

[N6BY]

An open feedhorn without the focusing provided by the parabola has a very wide beamwidth. Like using a machete instead of a scapel for a surgery. It will provide a general idea of the signal presence and general direction. I would expect to see spikes of varied amplitudes when using an open feedhorn, strong signals from direct line of path and weaker from reflected. The weaker signals are increasing the noise floor, but are not likely to a level to swamp the lnb conversion or tuner.

The beamwidth necessary to illuminate my dish is approx. 120 degrees. So by doing the open feedhorn test I know that there is 5G in at least 3 directions. And there will be more -- I recently received a postcard from Verizon advertising 5G home internet for $25 a month, so there will soon be 5G coming from nearly all direc†ions, as I am surrounded by homes on the ridges above my house.

They can (and will) install 5G small cells on streetlights in as little as 15 minutes: AT&T is Using Streetlights to Boost 5G Deployments . Most streetlights already have a power connection at the top. That is why 5G snuck up on me so fast -- I didn't see any new cell towers so I thought I was fine.

 

[N6BY]

I took a close look at my Unimesh 10' dish today and it already has unused holes drilled around the outer rim. Looks like it came that way from the factory. Not sure why? So all I have to do is get 16 3' long sticks of wood and 16 screws that fit the existing holes along the outer rim. Then I can wrap the mesh around it and see what performance I get with an unfiltered LNBF.

I think there is about a 30% chance that this will work. Will find out in a day or two.....

 

[Tower Guy]

If your shielding of the dish doesn’t solve the problem you could also try shielding the feedhorn. A cylinder made of hardware cloth might do the trick.

 

[primestar31]

I took a close look at my Unimesh 10' dish today and it already has unused holes drilled around the outer rim. Looks like it came that way from the factory. Not sure why? So all I have to do is get 16 3' long sticks of wood and 16 screws that fit the existing holes along the outer rim. Then I can wrap the mesh around it and see what performance I get with an unfiltered LNBF.

I think there is about a 30% chance that this will work. Will find out in a day or two.....

Don't use wood, it'll swell when it gets wet and cause issues. Also, those may be weep holes for water, so it doesn't freeze in Winter and bend the rim. Though I think you are in California, so don't need to worry about freezing.

 

[N6BY]

If your shielding of the dish doesn’t solve the problem you could also try shielding the feedhorn. A cylinder made of hardware cloth might do the trick.

That was my first attempt. Unfortunately it didn't work. The only solution so far is the Titanium C138. But I am going to attempt a 3 foot high ring around the dish (just as an experiment).

Don't use wood, it'll swell when it gets wet and cause issues. Also, those may be weep holes for water, so it doesn't freeze in Winter and bend the rim. Though I think you are in California, so don't need to worry about freezing.

It doesn't rain in my part of California anymore.

Back to serious - I'll see what I can find at Home Depot for cheap. If I can find metal bars I'll go for that. Otherwise its going to be wood, which I can paint for some protection. I don't plan on leaving it installed over the winter because the wind will send it flying, and its going to be very ugly.

 

[N6BY]

Don't use wood, it'll swell when it gets wet and cause issues. Also, those may be weep holes for water, so it doesn't freeze in Winter and bend the rim. Though I think you are in California, so don't need to worry about freezing.

It will be waterproof. I bought some 1/2" PVC and screws. I got the PVC cut and drilled and installed 8 of the 16 pieces on my dish last night before it became too dark to continue. Will finish this later today and test it.

 

[N6BY]

Today I built and tested a 3 foot high rim around the dish using 1/16" mesh and it failed to keep out 5G interference.

I think I can see why it's failing -- the mesh on the bottom side of the dish needs to be taller. And maybe I don't need any on the top.

If your shielding of the dish doesn’t solve the problem you could also try shielding the feedhorn. A cylinder made of hardware cloth might do the trick.

Although I tried something similar to this a couple of months ago, I think I did it wrong. For my next attempt I am going to make a 120 degree cone out of mesh and put it over the feedhorn, as you suggest. Hopefully it won't "shadow" too much of the dish or create unwanted reflections. Will know tomorrow....