Signal Strenth VS Signal Quality

[AcWxRadar]

This was an old post originally, couldn't reply to that, but I thought it was important......

Don't even pay attention to the signal strength ,it means nothing ... it's all about Quality

as jayelem said dont worry about signal.....quality is all you need to worry about

Jayelem and Iceberg,

I need to jump in here and disagree with you "slightly".

There is a definite difference between the "signal level" and the "signal quality" that you read off of your FTA receiver.

Your FTA receiver has two graphical bar graphs which display two different items, one displays signal level and one displays signal quality. They are both important indicators.

The signal level is basically a measure of the RMS current that is carried throughout your cable from the receiver to the LNBF and back. The minimum is just the basic noise floor from the LNBF itself. If you have a good LNBF and just lay it on the shop bench, you should detect some level of signal here. It will be in the red zone, but something should be present and it should not be at zero.

If it is at zero, the LNBF is dead or the receiver parameters are not set up to match the local oscillator of the LNBF.

The signal quality is a measure of the digital signal quality of the received signal from the satellite and reveals how high above the noise floor the transmitted satellite signal is. The higher this bar graph reads, the better or greater the signal from the satellite is over the basic noise floor of the LNBF itself and any additional noise from external terrestrial interference or solar interference sources.

You need to monitor the signal level just as well as the signal quality to ensure that your entire system is properly connected and fully operational.

Therefore, the signal level is not entirely meaningless. It is an important indicator and an important troubleshooting tool.

If the signal level reads very low or is non-existant, you might have too long of a cable run, an open circuit, a defective LNBF or a LNBF parameter set incorrectly, something that doesn't match the LNBF that you are using.

If the signal level reads very low, it might also tell you that your DC voltage at the dish motor or the LNBF may be too low to control either device, so be aware of that as well.

Normally, we ignore the signal level because we don't generally run into a problem with it. However, it is still very critical and therefore you must monitor it. If this shows too low or is at zero, you won't even be able to detect your signal quality.

Jayelem and Iceberg, you are not stating anything wrong, but you are not stating the most accurate overall picture. There is a definite reason for having the signal level meter. Most often we overlook this and just expect it to be something that is taken for granted, but for those who are new to this realm, we should explain a few of these items with more detail. Just so they understand the reasons why. I hope you guys don't mind my constructive critisicm.

AcWxRadar

 

[Mr Tony]

The only time I look at the signal strength meter is when I am ghetto moving the C-Band dish, the Pansat 1500 fluctuates between 69-85 when I am near any satellite but lowers to a reasonable 72-73 when its locked on the correct transponder. Stgrenght on a LNB usually shows at the same no matter where the LNB is..if its no where near the dish or not aimed at a satellite.

I've seen the Pansat show signal strength of 65 or so and quality of 99 with a Universal LNB. Dont ask me why it does that but the signal strength is whacked with a Universal

If the signal level reads very low or is non-existant, you might have a LNBF parameter set incorrectly, something that doesn't match the LNBF that you are using.

Pansat shows the same level regardless of LNB LO whether it be a KU LNB set to 10750, 10600 or 5150. I just wont get any quality unless its set properly

 

[Hermitman]

I respectfully disagree. The signal quality is not a measurement of RF energy but of the amount of error correction occuring, thus indicating the quality of data flow. For example, if the signal quality is 100%, that means that 100 percent of the data flow received is being processed without any error correction having been applied. If the signal quality is 50%, then only 50 percent of the data blocks are being processed without data error correction. (These numbers vary among receivers) In other words, if you strive for the highest number on signal quality, you'll get a better picture because of less error correction. And it doesn't really matter what your signal level reading indicates (as long as you have something normal) when you look for the highest signal quality. Good luck.

 

[AcWxRadar]

I respectfully disagree. The signal quality is not a measurement of RF energy but of the amount of error correction occuring, thus indicating the quality of data flow. For example, if the signal quality is 100%, that means that 100 percent of the data flow received is being processed without any error correction having been applied. If the signal quality is 50%, then only 50 percent of the data blocks are being processed without data error correction. (These numbers vary among receivers) In other words, if you strive for the highest number on signal quality, you'll get a better picture because of less error correction. And it doesn't really matter what your signal level reading indicates (as long as you have something normal) when you look for the highest signal quality. Good luck.

Hermitman,

You misread what I was stating. The SIGNAL LEVEL is an indication of the RF signal (noise and carrier both). I was not referring to the signal quality.

The SIGNAL LEVEL is a measure of the total RF signal. If it is high and in the "green" then the actual RF carrier signal from the satellite is above the general "noise floor" of the internal amplifier within the LNB and any TI or solar radiation noise that the the receiver might also be reading.

If it is high, but still displayed in RED, then the receiver is not discerning that the signal is anything valid, but rather just more noise.

The point is that SIGNAL LEVEL should not be ignored completely as it is a measure of a valid signal. It is total RF signal (general amplifier and background noise AND the RF signal from the satellite). If the receiver displays this SIGNAL LEVEL with a high "green" indication, then that means that the receiver is able to identify the RF carrier signal which is above the noise floor.

Your SIGNAL QUALITY will be meaningless if the receiver cannot pick the SIGNAL LEVEL out of the noise level to begin with.

The SIGNAL LEVEL is also a good indicator of your cable or LNB quality as you should be able to compare a short run of cable against a long run of cable and measure a difference, whether you are comparing just the amplifier noise and background noise or a valid carrier signal. If the cable length is very short, you should detect a fairly strong noise floor. If you add 200 feet of cable, you should witness this level decrease.

If you are aimed at any satellite, you should detect the RF carrier and the receiver should be able to identify it as a valid signal and not just more noise. If you add more cable length, then obviously this signal will decrease, so it is a good indicator of your overall cable and switch and LNBF health and whether or not the cable length is too great for your receiver's tuner to handle.

The main point or objective of my post was to clarify that the SIGNAL LEVEL display has a purpose and should not be completely ignored. It does inform you of something that is important. Also, the signal quality reading would be meaningless IF your receiver cannot pull out the signal level from the noise to begin with.

Therefore they both go hand in hand, but each signal representation is a valid indicator of something slightly different and the SIGNAL LEVEL readout should not be ignored.

Radar

 

[pendragon]

The signal quality is not a measurement of RF energy but of the amount of error correction occuring, thus indicating the quality of data flow. For example, if the signal quality is 100%, that means that 100 percent of the data flow received is being processed without any error correction having been applied. If the signal quality is 50%, then only 50 percent of the data blocks are being processed without data error correction.

Perhaps this is true for some receiver(s), but I would be reluctant to generalize. I was reading through the tuner driver for the DVB World 2104 USB box and it appears there are several parameters available from the hardware registers:

1. Signal Strength, derived from current AGC value
2. SNR, in units of 0.1 dB with maximum of 30.0 dB
3. BER (bit error rate), units of 1.0e-9 (this number is a bit of conjecture)

The second appears to be the one normally associated with signal quality. For a given modulation type, symbol rate and FEC one can calculate the SNR required to produce a desired BER. I am inclined to believe many receivers provide some scaling of SNR as the SQ.

 

[Mr Tony]

Heck some of the Fortec receivers dont even have a signal strength meter....just quality

 

[pendragon]

You misread what I was stating. The SIGNAL LEVEL is an indication of the RF signal. I was not referring to the signal quality.

The SIGNAL LEVEL is a measure of the total RF signal. If it is high and in the "green" then the actual RF carrier signal from the satellite is above the general "noise floor" of the internal amplifier within the LNB and any TI or solar radiation noise that the the reveiver might also be reading.

If it is high, but still displayed in RED, then the receiver is not discerning that the signal is anything valid, but rather just more noise.

For most, if not all, receivers the signal level is the amount of energy in the passband, regardless of whether it is the desired signal or noise. I can point my dish at dark space and crank up the gain of my amplifiers to boost the background noise to get any signal level reading I want, including "green". This is an important value, though, because if there are too many losses in the distribution chain from the LNB, your receiver will not have sufficient signal level to compensate with its AGC. Signal quality on the other hand represents some form of SNR and indicates the actual quality of reception.

 

[melgarga]

Signal Quality, be it an inverse representation of raw BER, S/N, some factoring of agc (analog rx's use the agc to indicate relative strength) , or a calculated value using all available data, it all basicly gets you the same result, the greater the displayed value, the less prone to loss of video caused by inclimate weather or other uncontrolled occurances.
As to Signal Strength, I have never liked that tag for this indicator. I prefer the label LNB/Cabling/DC Power health indicator and as AcWxRadar said, is a very basic, but relevant go or no go indication of the hardware status. The 'variance' seen is based on total lnb power loop current. Of course the longer the run, the higher the 'loop resistance", the greater the voltage drop resulting in less current draw. If you tweak to the edge of a usable Quality value (using variable polarity, azimuth whatever), and unless it is already saturated ( beyond the measurable scale) you can see a slight shift (increase) in "Strength" as the signal quality indicator increases. The lnb is loading, ie; working, and is drawing add'l current. On the other hand, cycle thru the available LO's and you can watch a diminishing "Strength" reading, as the LNB becomes more mismatched (unloading) and uses less current.
The absense of a "Signal" indicator on the Fortec is an unfortunate design flaw. As has been presented here, the "Signal Strength" is so taken for granted, it is often overlooked, yet is a valuable status indication when troubleshooting.
If you dont 'know' your LNB/Cabling/DC power is in good working order, you could spend hours trying to positition an antenna assy that is essentially non functional.
I just wish the industry had used a better description of what this feature actually is. The term "Signal Strength" is quite misleading.

 

[glen4cindy]

Heck some of the Fortec receivers dont even have a signal strength meter....just quality

True. My Classic NA only has 1 meter. My Lifetime Ultra has both and the Twinhan has both.

 

[B.J.]

While I generally ignore signal level and concentrate on the quality reading, I agree with those who say that the signal level is quite useful at times, and for many reasons, many of which were mentioned above.

Re zero signal... I agree that this is a good indicator of either a bad coax, switch or LNB. I've had several occasions where suddenly I was getting zero signal, and found that my LNB had been fried, and a couple other times when my switches were fried, and the zero signal is a quick indicator of a severe problem.
Also, the background signal level at the low end of the band vs high end of the band is often an indication of the quality of the coax, and/or switches. Ie I create these spectrums of the band with a BL-1030 and a program called BLSCAN, which creates a chart of frequency vs signal strength. I look at two things, the height of the signals above the background noise, which is indicative of how strong the signal actually is, but I also look at the slope of the background signal floor. Generally, on Ku, as you go from say 11700-12200, the background noise or the valley floors between the peaks, generally decrease as you go up in freq, due to signal loss in the cable and other components (this is generally reversed on C-band since the LO freq is above the signal frequency). I don't worry about slopes resulting in a loss of 5-10%, but when it becomes greater than that I begin to suspect that I have a problem with the cable or switches. In my system, I usually see a background around 45-50%, with peaks up into the 60-70% range on strong signals, ie I like to see signals that are 10-20% above the noise floor. Recently, I've noticed that my noise floor is pretty flat up to about 12100 on Ku, and then falls off pretty rapidly, sometimes down to as low as 10-15% at the high end, so I clearly have some issues at the higher end of the band. I haven't had time to diagnose it yet though. I've also noticed that I have a lot of zero signal level situations on the Ku on my BUD, and I think that this is related to a problem with the lnbf voltage on my Drake receiver on Ku.

Signal level is also important, when blind searching for a satellite, before you are close enough to see quality. Generally, even though you tend to get a signal level reading even when not aimed at the sat (and I have not observed that it is flat when not on the arc, but instead I have observed hot spots where I get quite high readings when aiming much lower or higher than the arc, which gets confusing at times), when you start getting close to the sat you're looking for, you'll usually see the signal level increase, helping you find the sat. The thing about receiver signal levels vs the hand held meters is that receiver meters are generally looking just at a transponder, while thos hand held meters indicate over not only the whole 500 MHz IF band, but also at least 500 MHz above this, so that it registers both the regular Ku band as well as the DBS above it, so hand held meters are often hard to use to locate the lower power regular Ku band. One thing that I've done is to use an OLD analog receiver that has a feature where it runs through the 24 channels at relatively high speed, continuously, this receiver also has a signal level connection on the back to which I can connect a voltmeter. When I'm searching for a sat with a fixed dish, I set that receiver in the fast scan mode, and watch the voltmeter, and when no-where near a sat, the voltmeter just sits there hardly moving, but when it gets on or near a sat, the voltmeter starts jumping up and down, indicating signal over floor. This has been very useful at times.

Another senario where signal level is important is when there are signals of the same freq/SR on two adjacent satellites. If you're tuning in using just quality, often times you get higher quality when you are actually moving the dish off peak aim, since you are taking the dish away from the interfering signal on the adjacent sat. In this situation it may well be that you want the aim to be off a bit, but the point is that using signal level AND quality allows you to at least figure out why you're getting unusual readings.

Anyway, while in general, I ignore signal level when peaking on a sat, signal level is quite important for a lot of reasons.

 

[AcWxRadar]

While I generally ignore signal level and concentrate on the quality reading, I agree with those who say that the signal level is quite useful at times, and for many reasons, many of which were mentioned above.

Also, the background signal level at the low end of the band vs high end of the band is often an indication of the quality of the coax, and/or switches. I create these spectrums of the band with a BL-1030 and a program called BLSCAN, which creates a chart of frequency vs signal strength.

This is very interesting! I can perform a simulated signal sweep with my Super Buddy meter that I think is somewhat similar to what you are doing above. I need to purchase a noise generator in order to do this properly, but I believe I can use the L-Band signal direct from the LNBF that is aimed at a known good carrier in about the same manner, just to get a general idea of the quality of a single cable drop.

http://www.appliedin.com/www/assets/products/SuperBuddy/downloads/SuperBuddy_CableSweep.pdf

Signal level is also important, when blind searching for a satellite, before you are close enough to see quality.

One thing that I've done is to use an OLD analog receiver that has a feature where it runs through the 24 channels at relatively high speed, continuously, this receiver also has a signal level connection on the back to which I can connect a voltmeter. When I'm searching for a sat with a fixed dish, I set that receiver in the fast scan mode, and watch the voltmeter, and when no-where near a sat, the voltmeter just sits there hardly moving, but when it gets on or near a sat, the voltmeter starts jumping up and down, indicating signal over floor. This has been very useful at times.

B.J., that is a really cool idea! Nice little trick!

Anyway, while in general, I ignore signal level when peaking on a sat, signal level is quite important for a lot of reasons.

I do monitor the signal level reading on my Coolsat, even though I have my fixed and motorized dishes already aligned. Every once in a while I take a peek at the signal level and compare it to what I had originally to monitor for any abnormal changes.

I started doing this because I had a run of bad luck with some DiSEqC 4X1 switches. I found (by accident) that port 3 of the switch would begin to fail early in the switches life and the signal level would steadily drop until it died, then port 4 would start exhibiting similar symptoms until it became totally unusable, too.

I began to test each port of the switch with the same L-Band freq before I permanently installed the switch. By observing if there were any changes in signal level on port 3 or 4, (or any port for that matter) I wouldn't use the switch. After ordering several DiSEqC switches, I finally found four which showed equal and strong signal level on all four ports. These four switches are still running OK five years later.

I also monitor the signal level when we have really wet weather or when the temperature is fluctuating and causing a lot of dew in the morning. I use silicone dielectric grease on my connectors to deter any moisture entry, but sometimes I still find problems. I can tell when it is degrading by monitoring the signal level.

Radar

 

[melgarga]

One thing that I've done is to use an OLD analog receiver that has a feature where it runs through the 24 channels at relatively high speed, continuously, this receiver also has a signal level connection on the back to which I can connect a voltmeter. When I'm searching for a sat with a fixed dish, I set that receiver in the fast scan mode, and watch the voltmeter, and when no-where near a sat, the voltmeter just sits there hardly moving, but when it gets on or near a sat, the voltmeter starts jumping up and down, indicating signal over floor. This has been very useful at times.

That's pretty neat, like a po' boys analog display spectrum analyzer. That gives me some ideas..........lol

AcWxRadar,
Have you seen any consistancy in failure rate vs mfgrs of the DiSEqC switches you analyzed? I know the cheapie 2 for $5 deal ones cant be all that, but the Cheitas are supposed to be pretty reliable, and electronicly 'rugged'. What brand did you finally settle on for 5 years of reliability?

 

[AcWxRadar]

That's pretty neat, like a po' boys analog display spectrum analyzer. That gives me some ideas..........lol

AcWxRadar,
Have you seen any consistancy in failure rate vs mfgrs of the DiSEqC switches you analyzed? I know the cheapie 2 for $5 deal ones cant be all that, but the Cheitas are supposed to be pretty reliable, and electronicly 'rugged'. What brand did you finally settle on for 5 years of reliability?

Melgarga,

Most of the "el-cheapo" switches that I received (like the ones you get as a freebie with the purchase of the receiver - like a prize in a box of Cracker Jacks) were about as good as the quality of the prizes in those boxes! Many of these were dead right out of the box or had some defect to them.

However, the specific switches that I was experiencing this "oddball" failure with port 3 and port 4 just happened to be Chieta switches and the ones that I have currently and still running after five years are also Chieta brand and the same model.

I hate to mention that this was the brand that I was having trouble with, because now I have had such good luck with this brand ever since.

I suspect that they may have had a bad production run as all of the bad switches were from the same source at the same time, so possibly something went wrong with that run or lot number or they were somehow exposed to some very strong ESD that was sufficient to cause them damage. There were four to maybe as many as six of these switches that failed in exactly the same manner.

However, I still personally use and recommend the Chieta brand.

Radar

 

[Blue Crystal]

All I know is that I use a Captive Works 800 receiver with my 10ft c/ku dish. I move it gheto style because the motor and arm is broken. I do not have an in-line signal meter. I use the "Satellite AV" print out of the sats that I can hit from my location.
I site with my compass and adjust my elevation according to to the print out. THEN I watch my signal strength meter on my receiver. I fine tune my dish until I can reach 70 or better signal strength. In most cases my quality signal increases with my signal strength. I then blind scan. When the receiver finds and programs a channel I then reset my receiver on the transponder where a channel was programed and then readjust my dish by watching both the signal and quality strength. I then blind scan again and usually pick up more channels.
Not the best way but it works.

 

[melgarga]

You bear the marks of a true sat hobbist Blue Crystal, but why pray tell are you continually adjusting the elevation on a polar mount dish? Once set to track the arc, setting and locking down the inclination, declination, and centered on your true south positition, the only adjustment necessary is to 'pan' E<---->W to the proper azimuth.
Are you are spinning that thing on the pole and using it as a 'zero skew' 1st generation DTV style dish? I cant see any other reason you would need to move the elevation (inclination) setting to tune to a different bird. If that is indeed how you are moving from one sat to another, we need to get you fixed up with the ARC!
All things said, points given for your diligence and resourcefulness, not to mention patience.

 

[Blue Crystal]

You are right, I am spinning the dish around.
Before my actuator arm broke it worked fine, right on track.
When the arm went and then my receiver shortly thereafter I decided i would go with a new receiver, first.
I have my eye on a few used arms around the area.
I'll be back to normal before long. I guess "normal" is a good way to describe me.
I know I'm having a lot of fun.
My only gripe is that out of several hundred channels, most of them are in Spanish

 

[nhulst]

The signal level is basically a measure of the RMS current that is carried throughout your cable from the receiver to the LNBF and back. The minimum is just the basic noise floor from the LNBF itself. If you have a good LNBF and just lay it on the shop bench, you should detect some level of signal here. It will be in the red zone, but something should be present and it should not be at zero.

If it is at zero, the LNBF is dead or the receiver parameters are not set up to match the local oscillator of the LNBF.

If this is the case, should it not be true that when I have the dish pointed correctly, LO set correctly, and frequency/polarity set to an active transponder, but symbol rate set wrong, that I should get high signal level in spite of zero quality? I'm pretty sure that has never worked for me... will try when I get home tonight.

FWIW, I'm using a Mercury II with the 1.53 firmware. I've noticed that when you're not on a satellite, the signal level bounces between 0, 1, 40, 41. Nothing in between.

 

[AcWxRadar]

If this is the case, should it not be true that when I have the dish pointed correctly, LO set correctly, and frequency/polarity set to an active transponder, but symbol rate set wrong, that I should get high signal level in spite of zero quality? I'm pretty sure that has never worked for me... will try when I get home tonight.

FWIW, I'm using a Mercury II with the 1.53 firmware. I've noticed that when you're not on a satellite, the signal level bounces between 0, 1, 40, 41. Nothing in between.

Nhulst,

That is precisely correct. But allow me to ensure that I explain it appropriately.

If all the satellites were to fall out of the sky suddenly overnight, so there is no chance of you detecting any valid signal whatsover... Then, when you connect your dish and aim it anywhere throughout the Clarke Belt or anywhere in the sky, you should read something on your signal level indicator graph (provided your receiver has one).

Obviously what you would read is simply amplifier noise from the LNBF and any solar radiation or TI interference noise. The signal level bar graph on the receiver will basically show it as such. Just some random and general background noise in RED ZONE. Nothing that the receiver can do anything with other than show you that you are detecting noise.

Now, put a satellite right in line with your dish antenna and purposely set the TP frequency correctly, but you set the SR incorrectly and far enough off from what would be appropriate. Now there is obviously MORE RF signal present overall, but since the receiver cannot identify it correctly, then it is just treated as "more" noise and therefore the signal level reading will be higher., but still not in the "GREEN" zone.

Therefore, the signal level should increase to some extent and normally to a noticeable extent if everything else is set appropriately.

If you are looking for this change or increase, you will notice it. But, it does have limitations and a lot of that is based upon your receiver and how it processes any signal.

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AcWxRadar

 

[nhulst]

Fortec Star must be doing something goofy in the Merc software because it doesn't work the way that it should per AC's description. My test case was ONN on H2 (actual symbol rate 6616 according to Lyngsat.) When locked, meaning any symbol rate I give it that's good enough to lock it, I get level in the high 80's and quality around 50. Going downward in symbol rate, 6400 is the first value low enough to cause it to lose lock. Immediately, level drops to 40 and quality drops to zero. No middle ground, and no variation other than a step function between locked and not locked.

So, in conclusion, I'm going to say if you specifically have a Mercury II with the same firmware I have, don't bother with the signal level.

 

[B.J.]

Fortec Star must be doing something goofy in the Merc software because it doesn't work the way that it should per AC's description. My test case was ONN on H2 (actual symbol rate 6616 according to Lyngsat.) When locked, meaning any symbol rate I give it that's good enough to lock it, I get level in the high 80's and quality around 50. Going downward in symbol rate, 6400 is the first value low enough to cause it to lose lock. Immediately, level drops to 40 and quality drops to zero. No middle ground, and no variation other than a step function between locked and not locked.

So, in conclusion, I'm going to say if you specifically have a Mercury II with the same firmware I have, don't bother with the signal level.

While I don't think that it is unusual for FTA receivers to jump from 40-0-40, or something like that, there have been numerous posts about the Mercury jumping around wildly in signal level. Mine used to do that occasionally, but what really bothered me was that when in one of the tuning menus, the level would just go to zero and stay there whenever you'd try to move the dish to peak a sat. I read other people posting about similar situation, particularly about the signal meter being innoperative in certain tuning menus. I found that when peaking a sat, the signal indication would go away, and I'd have to leave the menu, and come back in again to see the signal level, until finally I noticed that if I switched polarity on the signal I was tuning to, and back again, the signal would come back usually.
Then I was out at the dish with a hand held meter, and noticed that it wasn't the signal that was going away, but that the Mercury was actually cutting off the lnbf voltage, and the only way to get it back was to switch to horizontal polarity and back to vertical. I then noticed that when watching programs on vertical polarity, that they would go dead, and again, if I switched polarity, and back again, it would come back to life.

Anyway, since I've seen other people post about similar symptoms, I came to the conclusion that there are some serious problems with the Mercury, particularly with respect to it losing signal apparently due to it just randomly turning off lnbf voltage. It starts out looking like the signal level just jumping around at times, or going away in tuning menus, but it can get worse.