Well the questions keep coming in. So, I decided to write a post for the question. What is better, a bullet shape LNB or the conventional LNBF. Lets compared the GeoSat pro SL-1 Bullet (the worlds smallest LNBF that I know of) and a conventional linear LNBF. This topic has motivate us to produce a video in the near future, but for now here are the test results. We took the DMX-521 LNBF 70 db gain typical, L.O. Freq 10750, C/N .2 db typical and the GeoSat pro SL-1 LNBF 55db gain typical, L.O. Freq 10750, C/N .4 db typical. Right of the get go, the conventional design proved to have better reception (22% difference) It seems that the extra cone surface in front of the LNB does help? How do I know that? Well, I formed a cup shape with my hands in front of the Geosat lnb and my db gain went up 6 db’s. I took that a step further and made an aluminum funnel (cone shape) that emulated the conventional LNB design (to be fair) and placed it in front of the geosat LNB. This produced a 12 db increase. That would take the Geosats gain from 55 db gain to 68 db. That was a 20% increase.
Test number 2: Using a 36″ KU band dish, I measured quality and db strengths on a clear day. Test location North Idaho, azimuth 138.5 magn, elevation 31.0 degrees, skew -16.7. My Trimax SM-2200 reveled the following data with a pre-aligned satellite dish aimed at G-19 single LNBF. Test results: DMX-521= quality 89-91%, 89-90 db’s
GeoSat LF-1= quality 67-70%, 70-86 db’s the signal tended to jump around more.
Test number 3: Picture quality on both LNBF’s was good! All the transponders looked good (full spectrum results viewed with the Trimax sm-3500), no tiling, etc.
Test number 4: What remains? A good weather storm to run tests on stability for both LNBF’s.
Living in North Idaho I have been using my dual output DMX-522 lnbf, same specs as the DMX-521 and I have yet to loose signal with up to 4 ft of snow, heavy rains, hail, etc. It has proven its reliability beyond our expectations. We have great news, technology keeps getting better & better. We have the new line of LNBF’s the ESX-521 with 75db of gain. As soon as I get the new LNBF’s I will run another test to compare.
Single Output LNBF
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The cone at the front of an LNBF is not for gathering more signal. The larger white cap is actually covering the scalar, which looks like rings sitting inside larger rings. The scalar purpose in this larger conventional LNBF is for rejecting unwanted side lobes and preventing over illumination on the dish (the LNBF receiving unwanted signals or noise because it sees beyond the edges of the dish). The SL1 Bullet has been CAD designed to minimize the side lobes and properly illuminate the GEOSATpro 90cm dish without requiring the larger scalar. The conventional type of LNBF simply uses different technology to accomplish the same purpose. We have a beta project that adds an adjustable and positioning scalar to the GEOSATpro bullet LNBF and the result increases approximately an 8% Signal Quality gain on specific problematic frequencies. Other frequencies are marginal gains. A 12db or 20dB gain would be fantastic if that were possible, but that would be a whopping 400% to over 600% gain!(each 3dB of gain is equal to a doubling of power).
Cupping your hands or creating a cone in front of any LNBF will change the amount of area of the dish surface that is able to reflect signal into the LNBF. If the dish is experiencing interference from an adjacent satellite, limiting the area of surface reflecting that unwanted signal will increase the Signal Quality, but on other frequencies that are not experiencing interference, the Signal Quality will be reduced. There is a fine line between gathering as much desirable signal while rejecting unwanted signals that degrade picture and Signal Quality.
Signal Gain is a result of amplification, a scalar or cone does not amplify or produce gain. Scalars direct undesired signals away from the feed horn throat and if placed properly, deflect out of phase signals. They are passive devices that can increase signal thresholds, but not increase gain.
It must be noted that an increase in Signal Gain does not translate into better Signal Quality. Signal amplification actually reduces Signal Quality in a properly installed system. Signal Quality is usually much better on a lower signal gain LNBF because less noise is generated by the amplifier. Old LNBFs with 50 dB gains and 0.8 NR will normally outperform newer LNBF designs with higher signal amplification. Signal Gain is achieved by electronically amplifying any signal that is gathered in the feed horn. This means that both unwanted noise and desirable satellite signals are amplified. Higher Signal Gain does help overcome the loss of long or poor quality cables, but it does not provide higher Signal Quality readings or more reliable picture reception.
When measuring or comparing LNB or LNBFs performance the critical measurement is not how much Signal Amplification or gain an LNB cranks out, but rather the C/N (Carrier to Noise) ratio. CNR is a measurement of the ratio of good desired signal compared to the noise or unwanted signals either gathered or generated by the LNB. A LNB will have poor performance if it has high amplification or gain, but does not attenuate unwanted noise while increasing desired signals.
It is also extremely important to test LNBF performance across the entire frequency range and not just on a single transponder. A great LNBF will have uniform performance on all frequencies and not favor low, mid or high frequencies. It is also important to test how the LNBF performs on strong vs weak transponders. Often a LNBF which performs well on weak signals will get swamped and have poor performance on strong transponders or perform well on strong signals but have poor CNR on weaker.
In testing comparisons, optimize the dish aiming for each LNBF and quickly perform all testing in a very short period of time. Satellites are not completely fixed and are in constant movement or drifting within a defined area of the sky. Testing on a fixed dish without constant optimizing of the dish aiming will provide incorrect data. Be sure to list the frequencies tested, your location, the weather conditions, temperature (as these will greatly affect the signal quality) and document the CNR and raw BER readings. You will also note that a LNBF that gives great performance in one geographic area or temperature may not perform as well in other regions or conditions.
The gain or noise rating of an LNBF has minimal affect on reliable reception during inclement weather. The main reason that signals are lost or pictures break up during snow and heavy rain is the result of either an incredibly dense cloud mass which severely attenuates the KU band satellite signal or more likely rain or snow collecting on the LNBF cover.
Tip: Apply some Kings Rain Shield (No, not trying to sell you anything as we don’t sell it…… available at Best Buy or Sears for $9) or Rain-X to the face of the LNBF cover. Water will immediately bead off and not reduce the Signal Quality or decrease reception. Please note: Don’t use petroleum or vegetable based water repellents. these will attract dirt and can turn rancid!
Hope that this helps everyone understand what is happening beneath the white plastic cap!
Brian Gohl
Excellent brake down, thanks for taking the time to write this comment.
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