So when a larger dish popped up on the local Facebook for sale ads for £25 I bought it. With 1.2x1.15 and twin stabilizing arms and a decent 'tilt' mechanism (unlike the Triax) it looked good. So I duly fitted it and despite my finest tweaking, I can't get it over 7.8dB. The adjustment is noticeably finer but I was using my phone to remote access my desktop so could see the tiniest tweak making a difference. I wasn't expecting much improvement (as a percentage extra catchment area I'd hope for SOMETHING) but not a decline.
So maybe not all dishes are created equal.
Picking up another surplus dish next weekend, this time a 1.5M. I really WOULD hope for an improvement with this one!
Then there phase noise. With the same dish and feed I get 10 dB MER on BBC Arabic with a GPS locked PLL LNB vs 13 dB on a DRO LNB. That's a wideband signal, but illustrates the point that the far out phase noise of these locked PLLs is not all that good. Close in they are much better than DROs but still not perfect. So if you get good results on narrow signals but not on the beacon, its probably phase noise.
How do I know I'm looking at the transponder noise floor? On my SDR I get a raised 'HUMP' in which I see the edge beacons and other ops signals. I'm assuming that's it, so bigger isn't better, although I'm assuming it would reduce required uplink power?
- Pressed steel not so good as aluminium unless it has been copper plated, or solver plated - unlikey for the cheap ones.
Channel master solid dishes are not really solid, they are actually mesh dishes encapsulated in fiberglass. Still good but not if the mesh has corroded over time. If it has lived in a damp climate it might not be as good. Tin foil might fix but probably its scrap.
Mesh dishes in general are likely to be a bit down on solid ones - and remember wind loading for a mesh dish is not reduced as you might hope above a windspeed threshold.
The focal length and position of a suitable feed are very important, you can easily lose many dB by not being at the focus and the efficiency will be poor if the feed does not match the focal length.
There is often a good reason something is cheap.