Earlier today, I had started to draft a post here basically saying that except for the circular/linear capability, you'd get more bang for your buck with a cheaper lnbf. My example was going to be the Extreme II (or III, I can't remember), which cost me about $19, and has been an excellent lnbf. So I pulled up the specs for the two lnbfs, and they were pretty much the same, except for 2 things. The Extreme had more gain, which given the fact that they have equal noise figures and drift parameters, would suggest that it might be a better lnbf. However then I noticed that the Invacom had better cross polarization rejection. This made me think about a problem I've had with AMC21, in that I've been having a hard time with the horizontal side of that sat. So I decided to compare my Extreme to my spare Invacom. I was going to do this on my fixed Primestar which is aimed at AMC21. Only problem is that it's mounted on a PVC pipe bolted to an old log just sitting on the ground, so it isn't very stable. Rather than drag out a receiver and TV, I decided to take my computer out, and monitor the signal through my wireless LAN, watching the signal from my Twinhan on a desktop PC. Only problem with this is that I can't see the screen of my laptop in full sunlight, so I took out one of those picknik table umbrellas to provide some shade. Unfortunately, the umbrella fell, and knocked my not so fixed dish off the sat, so I had to find the sat again from scratch, which could have been hard using a Twinhan, but it worked out OK.
Anyway, I tuned in one of the AMC21 transponders, and was getting a good signal from the Extreme on my Twinhan, I can't remember, but it was something like 60/50, which is good for the Twinhan. Then, I switched to the Invacom. The signal went down to about 30/30, still good, but it "seemed to be" worse. I was tempted to just quit at that point, and say that the Invacom wasn't as good, however I decided to switch to the horizontal side, which was my reason for trying this. Previously, the 12150 transponder had been something like 35/30 with the Extreme, however with the Invacom, at first, I wasn't even getting a lock. However I played with the polarity a bit, and played with the aim, and I got it to lock, and managed to get the signal up to something like 30/25 , which is OK for the Twinhan... it usually loses lock somewhere down around 16-18 or so. So, again, the Invacom didn't seem to be performing quite as well as the Extreme.
HOWEVER, I decided to go inside, and look at the reception on my Diamond 9000. I looked at the S/Q on the 12150 transponder, and it was about the same that I had been getting before with the Extreme. However then I switched to the Lousianna PBS channel, which I hadn't been able to lock at all today with the Extreme, and have never been able to get a solid lock on it. Well, it is now giving me a solid 66/66 lock . The first time I have EVER been able to get a solid signal on that transponder!
So basically, this seems to demonstrate that different parameters are important for different things. While the Extreme seems to give me better performance on most QPSK transponders, and due to it's higher gain, seems to give higher S/Q readings, apparently the S/Q isn't that important when it comes to locking an 8PSK transponder. I'm not sure what the difference is, phase noise or cross polarization interferrence, or what, but the Invacom does seem to be better than the Extreme on 8PSK transponders.
Anyway, I set out to prove that the Extreme was better, and ended up convincing myself that the Invacom is better, even though it's a bit low on gain. And I'm happy about being able to actually watch the LaPTV channel, except when the wind blows, and tips over my log a bit. As soon as I find a suitable place to plant it, where I'm not blocked by trees or telephone poles, I'm going to mount the Primestar on a metal pole in concrete. Where I have it now, it's partially blocked by a tree, so I think I'm going to lose AMC21 when the leaves come out. I've already lost it on my motorized Fortec dish. I had AMC21 last week, but the leaves have started to come out, and now it's gone. (It's more than one tree with the Fortec, and some of them are maple trees, which I don't like to cut because they give me syrup. And the tree blocking the Primestar is also a maple.)