Satellite Dish Fade

[ChiefEngineer]

Here's one and I ask your help with thanks in advance.

Until 3 days ago dish was flawless through winter and even with some snow in it. Despite wind, etc, worked great.

Zenith C Band dish with XDS on it. XDS has a usable 6.0 signal that sometimes cuts in half with a fade effect. Up and down. No wind issues. Tightened all bolts, aligned, replaced lnb, checked alignment of feedhorn and 3 guy cables, checked cable to lnb then replaced for the fun of it. New cable new connectors to receiver.

Dish 5 feet away receives Unity 4000 on another bird. (AMC Something) No fade, no problem.

Up until last year the problem dish was retired as a new dish was placed for the unity 4000. At certain times of the year signal issues were noted, similar to what is happening now. Seemed as if this happened when least needed but could not trace to snow, rain, wind, or any other regular problem. (Checked for bees nest too and this isn't the problem) New dish was installed. Old dish was pulled, bolts tightened, new mount, new lnb, etc.

This is a Zenith dish. Has 3 guy cables for the single pole that protrudes from center of dish with a circle that is tightened by multiple bolts at center of dish. There is a center pole and the feedhorn pole comes out of this. (I wondered about grounding so drove a bolt through the center of the two poles and tightened like crazy.) I am sure they are well bonded now. Didn't seem to make any difference daytime. Bolts for panels are all tight. Has a ring that connects around outside of dish.

Problem started 2 days ago and we have had leaves on trees for weeks now. Odd thing is the issue starts at dark seemingly now (past 2 nights) and eventually goes away. First night I thought I had it fixed after checking the problem then it came back. I finally went to bed but later in the night the problem cleared on it's own. The problem returned at dusk. (if it was dew why now? Why does it clear after a few hours?)

Unity is aimed same direction as it was on old dish, no TI. 5 feet difference in location between Unity dish and XDS. XDS was flawless until 2 days ago. This is an issue I believe with the dish. It has no regular resolution.

Because the problem had been there in the same form with the Unity 4000 and was there twice a year I am wondering if anyone has any possible thoughts on fixing the problem?

 

[PTBoardOp94]

XDS has a usable 6.0 signal that sometimes cuts in half with a fade effect.

6.0 dB of signal? You should be getting at least 10 dB on that readout, more like 14-15. The XDS will fluctuate about 1 dB in normal operation, and something like 5.5 dB is the minimum to receive any programming.
Troubleshooting is another problem altogether. My first stop would be to ensure the dish is still properly aligned with one of those satellite field strength meters.

 

[joep]

Odd thing is the issue starts at dark seemingly now (past 2 nights) and eventually goes away. First night I thought I had it fixed after checking the problem then it came back. I finally went to bed but later in the night the problem cleared on it's own. The problem returned at dusk.

Have you actually been there at dusk to observe the antenna assembly? It's not always bees, and the critters don't always want to make the feedhorn a permanent home. I've had birds decide they want to perch themselves in the feedhorn at dusk..... they only stay a few hours, then they go away. They also seem to be creatures of habit, so it happened on a daily basis.

 

[Lazy J]

XDS has a usable 6.0 signal that sometimes cuts in half with a fade effect.

6.0 dB of signal? You should be getting at least 10 dB on that readout, more like 14-15.

I agree, you should be getting an eb of 14-15. I have installed many XDS receivers and I won't accept less than a 10. What size is your dish? It should be at least a 2.5 meter (8 feet) dish. Also, are you using the same LNB from the old dish? You may want to try a new LNB.

I use a Sat Buddy to peak in my signal.
http://www.appliedin.com/www/products/SatBuddy.html

I also use dish pointer to get my Azimuth and Elevation.
http://www.dishpointer.com/

 

[CaptBob92]

I thought I was the only one having a problem with the XDS-pro . I had a similar experience.

I'm running a 15 foot dish, peaked it up, adjusted the lnb, replaced connecters and jumpers. Cleaned and covered the poloroter, trimmed the trees around it etc. My old Starguide III runs fine as does an ABR200 also on the dish. The first XDS -pro I got was on a Citadil carrier and I got a 10 to 11 edno on it at maximum peak. However, the second XDS I got was on a Clear Channel carrier and ya, I get only slightly better than a 6 on it. I tried everything, in line amp, tieing it directly to the dish and bypassing my multi output unity gain amp, even bought a new multi output amp with one port feeding at a higher level out than the others. Still never got the XDS-pro on CC to go above 6 and ya, it does occasionally fade in the evening. I'm out of ideas and low and behold I'm now told another one is coming to replace the ABR200.

BTW I even had them ship in another XDS-pro also on a CC carrier to check and it did the same thing.
I'm stumpted. Anybody help?

 

[ChiefEngineer]

First off, yes, would LOVE to have a better signal. Another XDS here in Indiana is also similarly low signal. No one can explain it. The low elevation does bring trees into play at my site. We have a 10 foot dish. 50 rf 6.0 EBNO. Squelch is 3.5.

At the last site, same rotten EBNO, it is a 10 foot dish on a roof. This site doesn't have the fade issues though.

I have the good fortune of living at the site. The dish is outside my back door. We are non com and the house is also the studio.

I have replaced the LNB and feedhorn. Literally the only thing left is the dish. I sit and watch the receiver fade and go look at the dish. I look off the end of the dish to see...nothing. Look in the feedhorn too. Nothin. This is a Citadel feed. Floodlight, Ryobi portable flashlight, etc. to look at everything. No idea.

I can beat the crap out of the dish components with a pvc pipe and get no measurable changes that affect the signal. (Checking for loose stuff) During the day I checked all the bolts AGAIN, looked at anything that might be involved and no luck. The Amityville Dish. Cable and connectors are new. We are on cable 3 to this with no change. I can put the receiver at the dish and get the same results.

Should the single pipe feedhorn be grounded to the dish? I beleive so. The other dish we use has 4 metal pipes that meet at the feedhorn from the dish perimeter. This has the pipe from the middle of the dish.

 

[rfburns]

I would look at the signal with a spectrum analyzer. You will be able to verify azmuith, elevation and feed polarity. Adjust polarity for best compromise between best on-transponder signal and least adjacent-transponder signal.

RFB

 

[Lazy J]

My general troubleshooting modus operandi is this. If possible, take the XDS receiver out to the dish. Make a good coax jumper and connect the receiver directly to the LNB. Then, begin by adjusting the azimuth (horizontal) until I find the peak. Next, adjust the elevation (vertical) for a peak. If needed, go back and for between azimuth and elevation until you find the highest peak possible. Next, move on to the LNB. There is usually a polarity adjustment somewhere on the feedhorn. Rotate for a peak. The receiver will only lock on it's assigned transponder, so no need to worry about peaking in the wrong satellite.

That should give you your best possible signal level. If you still have poor signal, measure the dish to see if it's warped. Measure from rim to rim horizontally and then vertically. The measurements should be basically the same. If the dish is warped, it will spread out your focal point and lower your signal level. Still no luck, I usually try a new LNB. Also, inspect the feedhorn assembly for water or dirt build up.

Worst case scenario, I call another station in town and test my receiver on their dish. This will verify if my receiver is bad.

 

[boiseengineer]

Premeire seems to normally run less than ABC. WWOne also.
During sun fade ABC hangs in there a lot longer than any of the others.
ABC's Starguide used not drop out at all. (3.8 M Comtech)

 

[ChiefEngineer]

Premeire seems to normally run less than ABC. WWOne also.
During sun fade ABC hangs in there a lot longer than any of the others.
ABC's Starguide used not drop out at all. (3.8 M Comtech)

You mentioned sunfade. What a hoot. Sunfade on this was less than the AMC Dish. Still noting spotty reception. I guess if it gets bad enough this will create a total failure.

 

[Doctor_Technical]

Lazy J has a good outline to follow. Some finer points to consider:

You say your feedhorn is guyed. Is it possible that unbalanced guying has pulled the feedhorn off center, twisted it somehow, or has it pulled the feedhorn inward (toward the reflector), the results of either being that the feedhorn is no longer in the proper focal point? There is a reason that pro dish makers use multiple fixed spars to precisely locate the feedhorn.

Did you replace the feedhorn with the same model? What about your replacement LNB, is its performance as good or better than the previous unit?

To amplify on how Lazy J is suggesting to test the reflector geometry: stretch two lengths of string from edge-to-edge across the dish in a "X" pattern. If the rim is round and true, the strings should touch where they cross. I have seen this one time on a very-large (5-meter) uplink dish, where the fix was to "re-bend" the dish via a guying system. Gave us our missing several db of gain back.

You mention:

The low elevation does bring trees into play at my site.

Either they are or they are not. Yeah, I've shot through towers and a few tree limbs when there was no other choice, but I also ate up all of my fade margin. Remember Fresnel zone clearance rules apply to microwaves, too, meaning you may need to chop a wider "hole" through the trees than you think (or raise the whole dish via a pedestal or tall pole).

Finally, can you take big swing at the problem? Can you drastically move the dish (or get a loaner) to another part of the property? This gets into sat-math well beyond my pay grade, but I recall from my SCPC days that we were sensitive to a thing called "ground noise", meaning interference and reflections from anything not in the sky.

Just some ideas. Let us know what you find.

 

[littlejohn]

And, when you do the 'string test', be sure to reverse the strings if they touch the first time... that is, restring with the initial top string on the bottom. It is possible for the top one to be pulling the bottom one down instead of just touching it, and it doesn't take much warp to kill the signal significantly.

 

[ChiefEngineer]

I am legally blind and use my son to help. He is 13. He has also run wires, wired punch blocks, and is willing, if not all the time, at least part of the time. This is our family ministry so he isn't quite as enthusiastic as I am about this. I AM excited about the nuts and bolts part of this.

The original strings are with the dish. The nylon used was covered well with, something. I replaced two of the 3 because some parts were brittle. We had gone through and re-tightened all the bolts and nuts. The dish was originally bought in pieces, and moved. We replaced rusted hardware when installed several years ago. Regularly brush rusty areas and repaint the galvinized hardware. Surface is aluminum so that has no irregularities.

Last night we pulled the feedhorn again and tore apart the electric "polaroter". Found it was not always going in the correct direction when 9v was applied. It sometimes switched direction. We put the whole thing back together today and then tweaked polarity. Tried 2 lnb's with the same result. During the day we tweaked it for the same signal we have always had. (6.0). (Maual rotation.)

We have had the same signal from day 1. Just now, at night and sometimes when it rains, we have lost signal. Found no moisture in anything. We didn't get an increase in signal but my 13 year old suggested music on hard drive. My wife wants to know why in the age we are in are we still using something akin to WW2 handitalkies. (old 20 lb portables.) Hams use circular yagi arrays. Wouldn't that look better on the roof as opposed to big dishes in the yard????

It is officially past the time we normally loose the signal. I wonder of the figure 8 movement of satellites has some relationship to the problem as it was great and just started. I installed Muzak dishes years ago and have run into many issues noted. Thanks for the help. Will post tomorrow with the results.

 

[ChiefEngineer]

The end result of all the tweaking was a 56 signal, up from 50. This did not affect the overall ebno. The ebno is at 6. something during the day now.

After my last post I checked the night time signal and found it had drifted to a 4.4 and would hit a 4.2 at times. If it is like the past few days I can expect it to drift back up during the day. The good news is that it did not drift low enough to mute the signal.

Having been doing engineering for 30 years I am very much perplexed by the problem. Despite my visual issues I can find no problem that would indicate the reason for the problem. I have never seen rf change at night. The trees that are at a distance do not wave as the signal does at night. clearly they do not mobe. My wife points out that from the dish angle they should not be an issue. Unlike the current Huskvarna commercial the trees do not grow at night.

I am tracking the AMC signal on the other dish 5 feet distant and no change.

The signal fade has been noted when the sun sets. Because this has also been when it rained the previous few days that was also at question. We are in a residential area. Anyone have issues with any computer generated wifi devices? My avcom spectrum analyzer was borrowed and broken, won't make that mistake again. I do not see the signal change though.

 

[ChiefEngineer]

A link shows that 4g is operating in the C band spectrum.

http://www.nd.edu/~mhaenggi/NET/wireless/4G/

So now the answer is not if but when? I guess because of the low elevation and the mutiple notes that this could be a problem means it will be.

 

[kenglish]

Have you removed the feedhorn and checked the inside (throat) of it and the LNB?

I've seen instances where bees and other vermin build their nests inside the feed. Then, when they return "home" for the night, their bodies absorb quite a bit of signal. Also, if there's a shroud (protective cover) over the LNA and waveguide assembly, look there for bugs...they can build up quite a bit of insulation in there, and cause some temperature-related issues.

You might want to look around a bit first, to see if you'll need protective wear. Think "beekeeper".
(You're not in dirt-dobber country are you?)

 

[ChiefEngineer]

Have you removed the feedhorn and checked the inside (throat) of it and the LNB?

I've seen instances where bees and other vermin build their nests inside the feed. Then, when they return "home" for the night, their bodies absorb quite a bit of signal. Also, if there's a shroud (protective cover) over the LNA and waveguide assembly, look there for bugs...they can build up quite a bit of insulation in there, and cause some temperature-related issues.

You might want to look around a bit first, to see if you'll need protective wear. Think "beekeeper".
(You're not in dirt-dobber country are you?)

Bees and hornets used to bee (pun intended) my best moneymaker on Sat Dish problems. I would have thought this the problem if I didn't know better. Did pull the feedhorn and took it entirely apart. (I use a protective cover on it btw.)

I am wondering about 3 or 4 g networks now though.

 

[kenglish]

Good though. Any wireless routers near the dish?
The ATSC guys say they are MAJOR sources of interference to DTV reception.

Are you using C-Band/Ku-band (with heliax, maybe), L-band (950-1450), or what?
Also, I remember the Cable head-end having a problem with a light dimmer or photoelectric switch on the light at their back door, just about ten or twenty feet from their dishes. The noise started at dusk, travelling down the coax lines' shields.

 

[Lazy J]

I know you said you tried another LNB, who is the manufacturer and what is the Noise Temperature of the LNBs you are using? If you get a lot of fade at sunset and night, it might be the LNB or the dish getting cooler.

 

[listner1]

Just another voice to say I've seen the same thing at several sites. Citiadel carrier with an ebno of 10 or 11, and Premiere around 6. One site has a new 2-degree compliant dish, and they get about a 14 on the Citadel carrier and about a 10 on the Premiere. So for whatever reason, the transponder that Premiere is on does not send out as good of a signal as Citadel's. Also, the Dial Global carrier seems to be nearly the same ebno as Citadel, although the downconverters in those receivers very a good bit from unit to unit. Westwood One's MAX uses a "signal quality" reference, so it's hard to compare, but during sunfades, WW1 seems to go out first, followed by Premiere. Quite often now, Citadel's carrier will stay on throughout.

However, I do not see much of a fade at night. These signals stay reletively close all hours.