Hi everybody,
After remaining unable to find out why my DMS LNBF most of the time won't switch from horizontal to vertical and back I used the advice I got earlier on this board and ordered a Norsat 8515 LNB.
Subsequently I followed tvpro's advice and mounted it on my brandnew National ADL RP1C dual hybrid mode feedhorn. It wasn't easy because the Norsat was delivered with a rubber isolation that actually was too small for the groove, but eventually it worked.
Today I went up to the roof to mount it into my 10 ft Unimesh dish. And there the problems started: the scalar rings and the feedhorn are made in one piece. Initially it just meant making a deep cut into the base of the hood of the dish, no big deal.
But then: the Unimesh dish has four legs to support the LNBF that are mounted like a cross on the dish. But the ADL only allows for screws on legs that are situated North-South and East-West. Sure, you can turn the feed and the legs will move along to allow for this so the LNBF ends up in a proper horizontal position. But that gives you no option whatsoever as to the distance between the LNBF and the dish center.
With the DMS LNBF I had done extensive tests to see what really gave the optimal result in terms of quality reception, but now I had to accept that the feed opening was a full 2 inches closer to the dish.
I know, I can try and work this out by accepting that in normal H or V position the dipole is at a 45 degree angle and then correct it by skewing, but it still feels strange. Besides, the larger diameter of the ADL scalar rings play a role as well, I don't think that I can really get the feedhorn at the same distance to the dish as the DMS was.
But..... Immediately I saw a huge improvenent! The DMS should have been equally good as the Norsat (both claim 15 degrees K) but the first result was staggering: on 55 West I received Rodnoy Telekanal very poorly, always freezing partially and now I had a 78% steady signal. Later on when I placed the teflon slab that was reduced to 70% but I guess that's normal.
Normality also came back in another way: where the DMS feed kept receiving circular signals with the teflon slab removed, with this installation the polarity issue seems to be restored: very little reception without the slab, not even on 40 East but once the slab is mounted at the first blindscan for Yamal at 49 East I get a handful of stations, mostly undisturbed. With the DMS and also with the combination of a Chapparal adjustable feed or a Chapparal Corotor combined with a Gardiner 25 degree K LNBF I only once during exceptional condition I managed to get a single channel from Yamal and that happened to be encrypted so this is really the first time I can actually watch tv and hear radio programmes from that satellite.
Exceptional results, thanks all for your useful advice. The only question that remains: should I leave things as they are, or yet later on try to experiment by increasing the distance between dish and feedhorn? This can't really be done the easy way because adjustment of the legs means at the same time a turning of the feedhorn. I thought of putting 1 inch spacers between the legs and the feedhorn but the feedhorn and the Norsat LNB together are so heavy that it might end up bending out of position rather than focusing perfectly well into the center of this dish.
I am tempted to leave it the way it is, hoping/assuming that the manufacturers of the dish and the feedhorn somehow were in tune with one another when producing their stuff. The f/d ratio of the dish is .40 and the recommended f/d rate for the use of the ADL feed is between .38 and .42 so actually things should be pretty good as they are. I'm just not used to not-measuring when I install a dish.
Well, further indoor experimenting will have to wait until tomorrow, in about an hour the first part of the Eurovision Song Festival from Düsseldorf will start and that's something that many of us don't like to miss.
After remaining unable to find out why my DMS LNBF most of the time won't switch from horizontal to vertical and back I used the advice I got earlier on this board and ordered a Norsat 8515 LNB.
Subsequently I followed tvpro's advice and mounted it on my brandnew National ADL RP1C dual hybrid mode feedhorn. It wasn't easy because the Norsat was delivered with a rubber isolation that actually was too small for the groove, but eventually it worked.
Today I went up to the roof to mount it into my 10 ft Unimesh dish. And there the problems started: the scalar rings and the feedhorn are made in one piece. Initially it just meant making a deep cut into the base of the hood of the dish, no big deal.
But then: the Unimesh dish has four legs to support the LNBF that are mounted like a cross on the dish. But the ADL only allows for screws on legs that are situated North-South and East-West. Sure, you can turn the feed and the legs will move along to allow for this so the LNBF ends up in a proper horizontal position. But that gives you no option whatsoever as to the distance between the LNBF and the dish center.
With the DMS LNBF I had done extensive tests to see what really gave the optimal result in terms of quality reception, but now I had to accept that the feed opening was a full 2 inches closer to the dish.
I know, I can try and work this out by accepting that in normal H or V position the dipole is at a 45 degree angle and then correct it by skewing, but it still feels strange. Besides, the larger diameter of the ADL scalar rings play a role as well, I don't think that I can really get the feedhorn at the same distance to the dish as the DMS was.
But..... Immediately I saw a huge improvenent! The DMS should have been equally good as the Norsat (both claim 15 degrees K) but the first result was staggering: on 55 West I received Rodnoy Telekanal very poorly, always freezing partially and now I had a 78% steady signal. Later on when I placed the teflon slab that was reduced to 70% but I guess that's normal.
Normality also came back in another way: where the DMS feed kept receiving circular signals with the teflon slab removed, with this installation the polarity issue seems to be restored: very little reception without the slab, not even on 40 East but once the slab is mounted at the first blindscan for Yamal at 49 East I get a handful of stations, mostly undisturbed. With the DMS and also with the combination of a Chapparal adjustable feed or a Chapparal Corotor combined with a Gardiner 25 degree K LNBF I only once during exceptional condition I managed to get a single channel from Yamal and that happened to be encrypted so this is really the first time I can actually watch tv and hear radio programmes from that satellite.
Exceptional results, thanks all for your useful advice. The only question that remains: should I leave things as they are, or yet later on try to experiment by increasing the distance between dish and feedhorn? This can't really be done the easy way because adjustment of the legs means at the same time a turning of the feedhorn. I thought of putting 1 inch spacers between the legs and the feedhorn but the feedhorn and the Norsat LNB together are so heavy that it might end up bending out of position rather than focusing perfectly well into the center of this dish.
I am tempted to leave it the way it is, hoping/assuming that the manufacturers of the dish and the feedhorn somehow were in tune with one another when producing their stuff. The f/d ratio of the dish is .40 and the recommended f/d rate for the use of the ADL feed is between .38 and .42 so actually things should be pretty good as they are. I'm just not used to not-measuring when I install a dish.
Well, further indoor experimenting will have to wait until tomorrow, in about an hour the first part of the Eurovision Song Festival from Düsseldorf will start and that's something that many of us don't like to miss.
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I also upgraded from a cheap CAD$50 LNBF to a ortho c-band chaparral feedhorn and 2 Norsat 3220 hi-stability LNB's. The performance gains were significant and similar to yours since I am now able to lock onto channels I couldn't before. I think it is mostly due to the extra stability of the L.O. in the LNB. Noise temperature is fine for comparing LNB's but L.O. stability is also very important.
