Channel Master Upgrade Project

[Tron]

Got an interesting item in the mail today. It's an honest-to-goodness Channel Master feedhorn (the model made for the 1M and 1.2M dishes that many of us have). Got this with a Norsat LNB attached to it on E-Bay for $32.25 shipped. Please see the pics below...

I bid on the item for the feedhorn alone, but the LNB seems like it may be worth something as well. It's a PLL (Phase Lock Loop) LNB, the kind used for data and broadcast video applications. See the Norsat 11009LA at http://www.sateng.com/catalog/category_mfg_search.asp?category=LNBs&mfg=Norsat

This LNB retails for $189.00, which was rather surprising to me. What makes this LNB different from most of the standard LNBFs out there is that it has an extremely high L.O. (local oscillator) stability. The L.O. stability on this LNB is +/- 100khz, as opposed to +/- 1mhz as typically found on LNBs such as the Fortec FSKUv. The down side is that PLL LNBs typically have a higher noise figure. This particular one is .9 (OUCH!!!)...

The question is, which is more important... low noise figure or high L.O. stability... in terms of low BER and high signal quality? This is a question I hope to answer tomorrow when I install this beast on my 1M Channel Master dish which is aimed at G-10R. I will post the results here. Note that this LNB is a single-polarity model, so I'll be stuck with the vertical transponders (no big deal, there are only 3 horizontal channels on G-10R that are FTA). If the performance of the Norsat is not satisfactory, I'll take it off and replace it with a C-120 flanged Invacom.

 

[Dishpointer]

Good find. Let us know how it works.

 

[Tron]

I don't have much time to work on it until later tonight/tomorrow, but I just removed the Fortec FSKUv and replaced it with this feedhorn/LNB. Within a couple of minutes (and without much peaking at all, its still not properly aligned) I'm getting a steady signal quality of 45-50 on The Tube. This is equal to the best I've been able to get on the Fortec.

Again, I need to take the receiver and monitor up there to peak it, this is just putting it up and playing with it for a couple of minutes. This is a .9 noise factor LNB!!!

 

[Stefan]

I don't have much time to work on it until later tonight/tomorrow, but I just removed the Fortec FSKUv and replaced it with this feedhorn/LNB. Within a couple of minutes (and without much peaking at all, its still not properly aligned) I'm getting a steady signal quality of 45-50 on The Tube. This is equal to the best I've been able to get on the Fortec.

Again, I need to take the receiver and monitor up there to peak it, this is just putting it up and playing with it for a couple of minutes. This is a .9 noise factor LNB!!!

I think the reason the noise figure is so high is simply because it's an old LNB. You can certainly get PLL LNBs that have noise factors as low as non-PLL LNBs. They're just really expensive. If it hadn't been for the noise figure of this LNB being that high, I'm sure youd have had to pay alot more for it. As for what's more important noise factor or LO stability, that's an interesting question and the answer probably depends on other factors like the symbol rate of the signal your trying to receive. It would be very interesting to see a comparision between your Norsat PLL LNB and an Invacom. I'll bet the results might be surprising to some.

 

[Tron]

Well, before I left I climbed back on the roof and turned the LNB a bit more. Got up to 61 quality on The Tube (with the level staying almost always in the 50s) before turning everything off.

One thing I have to check on also is the orientation of the probe on the LNB. If its installed for horizontal, which it may be, the feedhorn isn't performing at its best since I have it in a vertical orientation. I'll need to take it off and check on that before proceeding further.

 

[Tron]

I took the CM feed and Norsat LNB combo down this morning to check the polarity slab position. It was incorrect (angled instead of aligned correctly with the arrow on the feedhorn). So I took the LNB and waveguide off of the feedhorn and oriented them properly.

After re-installing the assembly and setting my skew at +43 (the proper skew for my location on G-10R) I was able to pull in a signal with a constant quality in the lower 50s and high of 60. This outperforms my Fortec LNBF, but only by about 10 quality points or so.

My conclusion is that the increase in quality I am experiencing is due to the fact that I'm using a matched feedhorn with the Channel Master. The Norsat LNB, while a PLL LNB, is probably not outperforming the Fortec. It's close, but the high noise factor of .9 on the Norsat is probably evening out the higher performance of the local oscillator.

The next step would be to replace the Norsat LNB and waveguide with an Invacom polarity-switching LNB with a C-120 flange. I don't have the budget for one of these right now, but I will keep my eyes open. With the C-120 Invacom, I will be comparing apples to apples with regard to the LNBs, since the feedhorn would be the same.