X-pol or IF crosstalk interference on 11263MHz
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Charlie
Hi all, Wasn't sure whether to reply to one of the specific threads or just go with a new one - but going with the latter. On my previous Inverto White Tech C120 quad LNB, since replaced after finding the V pol was near on 2dB C/N weaker(!) than the H pol, didn't find much added noise between the different output ports. As an interim measure I cobbled a flange onto a Labgear/Visiblewave VK4L LNBF with the feed cut off - definitely weaker kit (<1dB typ LNB noise rating) but brings the V-pol into usable range for me. Really I should have tested before/after realigning the pins inside it - squared them up when doing the mod so no idea what the "out of the box" Ku stage x-pol performance would have been like. Only thing I've noticed is that if I use two ports next to each other, doesn't matter which combination, I seem to lose around 0.3dB of C/N on each! Two different types of cable in the test too, as ran the two extra cables out later whilst fitting a dinky "minidish" for TV. So I don't think it's in the cable run, which is very short anyway - the PC is probably even barely a metre in a straight line from the dish. Evidently there is very poor shielding between the different outputs on this very cheap (yet still PLL) LNB causing crosstalk at the IF stage. Not really a problem - just thought I'd share my experience in case it helps anyone tweak a last extra bit of noise margin out.
Charlie |
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On 23/11/2022 14:25, Charlie wrote:
Only thing I've noticed is that if I use two ports next to each other, doesn't matter which combination, I seem to lose around 0.3dB of C/N on each! Two different types of cable in the test too, as ran the two extra cables out later whilst fitting a dinky "minidish" for TV. So I don't think it's in the cable run, which is very short anyway - the PC is probably even barely a metre in a straight line from the dish. Evidently there is very poor shielding between the different outputs on this very cheap (yet still PLL) LNB causing crosstalk at the IF stage.Charlie, Fascinating! What you suggest is perfectly feasible - IF cross-coupling. Mentioning Sky, do they use cross-polarised LNBs (I see two leads coming from mine) and do they have channels frequency offset between V and H, or co-frequency? I'm wondering how they might avoid the problem as I can't imagine they use the very best LNBs! David -- SatSignal Software - Quality software for you Web: https://www.satsignal.eu Email: david-taylor@... Twitter: @gm8arv |
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Ernst Lobsiger
On Wed, Nov 23, 2022 at 06:25 AM, Charlie wrote:
Wasn't sure whether to reply to one of the specific threads or just go with a new one - but going with the latter.Charlie, I'm not sure I understand very much of your HF tech talk. I for one see no problem with H+V on my Gibertini OP 125L and Inverto Black Ultra QAUD. I have 4 cables in a rather tiny tube that goes out 25m into the garden. The only thing that can be related somehow is my LNB switch ON/OFF issue: https://groups.io/g/MSG-1/topic/76210431#29731 Best regards, Ernst |
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Charlie
On Wed, Nov 23, 2022 at 02:48 PM, David J Taylor GM8ARV 🏴 🇪🇺 wrote:
Mentioning Sky, do they use cross-polarised LNBs (I see two leads coming from David,
Sky Q uses "wideband" LNBs that just have a H and V output of the full band with one LO frequency - incompatible with the old diplex, triplex with terrestrial TV etc as it spans 290-2340MHz! Older Sky/Sky HD etc and 'regular' Freesat is just standard "universal" LNBs the same as we're all using for this. There are only two pairs of TPs on there (Astra 2G, EU wide beam - 11265 H/V Astra 2E, UK spot beam - 11386H/V) on the same frequency that I can see but plenty are close enough to be otherwise overlapping in part of the bandwidth (I think 36MHz is standard?) They just get around it by blasting the signal down at levels we could only dream of - hence the ability to use the tiny mesh "Zone 1" 59x43cm dish, at least down here in London (I understand the "Zone 2" 77.5x62cm dishes are installed as a rule in Scotland due to the lower elevation to keep the rain margin up...). Unfortunately the Hauppauge card I use for that (and don't own a separate meter) only reports SNR in %... but it pegs the meter on the UK spot beams and hits 80%+ on the weakest (2G wide!) with that puny dish. And another one of those Labgear LNBs sold as "Sky compatible" despite having a circular feed not optimised for the elliptical dish. I believe it's something along the lines of 57 dBW EIRP on the UK spot and 54 dBW on the Europe wide... dizzying compared to what Eutelsat 10A affords with a meant-to-be 48dBW but I'll be damned if it is! Charlie |
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Charlie
On Wed, Nov 23, 2022 at 03:02 PM, Ernst Lobsiger wrote:
I'm not sure I understand very much of your HF tech talk. I for one see no problem with H+V on my Gibertini OP 125L and Inverto Black Ultra QAUD. Ernst, I believe different receivers interfering is a bit of a "known problem" in the TV world, particularly when it comes to faulty set top boxes. Not wholly surprising as the power has to be effectively commoned inside the back of the LNB... can see how that would give a "blip" when you turn one on/off. Just not for the duration you showed there. Certainly intriguing... Charlie |
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geojohnt@aol.com
Charlie, David and All,
Regarding the recent discussions, back in the good old days of analogue satellite TV, the H and V channels all had considerable frequency offset - but still overlapping.
I've been having a look around and see that now 'very small' frequency offset still seems to exist between some channels.
I don't see that many channels on 'well known satellites' are using exactly the same transmission frequency as EUMETCast do.
Having said that, Flysat list HVS-2 as 11.261 V and BS/HVS-1 as 11.263 H.
Is this a small degree of frequency offset?
I also found that Inverto seem to have updated some of their range of LNB's.
I don't see Black Ultra quad any more but a new version:
https://www.inverto.tv/lnb/447/quad-high-gain-low-noise-40mm-pll-lnb.
I can't find the specification of my Black Ultra quad LNB so cannot compare this new version.
Regards,
John.
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Charlie
John, I think that might be an error on Flysat's part - the Spectrum Spy screenshots that David posted a little while back look to be on the same frequency. As to the Inverto LNBFs - yes, there is an updated model and the widely-praised "Black Ultra" version has been discontinued. I have a single-output version of the new one and very underwhelmed (substantially outperformed by the aforementioned Labgear cheapo); many people on TV forums reporting that it is a dud too. Luckily for now the original style is still available where stock remains. I would try converting a new one to C120 to see if it's just the feed that's poor (I have a hunch it is illuminating far too much, on my Triax dish I had to run it pushed as far in as it would go) or if it's the actual LNB... but they have a square waveguide that complicates matters somewhat! |
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geojohnt@aol.com
Charlie,
>I think that might be an error on Flysat's part - the Spectrum Spy screenshots that David posted a little while >back look to be on the same frequency.
What was I thinking about?
It states quite clearly on EMETSAT's HVS-2 migration page that both V and H share the same frequency.
Regarding your comments on the new version of the Inverto Black Ultra LNB, this is a bit worrying.
I might just gently have a word with Inverto, who I did have quite a long series of contact with a couple of years ago, about this.
Regards,
John.
-----Original Message-----
From: Charlie <charlie.johnson119@...> To: MSG-1@groups.io Sent: Thu, 24 Nov 2022 14:40 Subject: Re: [MSG-1] X-pol or IF crosstalk interference on 11263MHz John,
I think that might be an error on Flysat's part - the Spectrum Spy screenshots that David posted a little while back look to be on the same frequency.
As to the Inverto LNBFs - yes, there is an updated model and the widely-praised "Black Ultra" version has been discontinued. I have a single-output version of the new one and very underwhelmed (substantially outperformed by the aforementioned Labgear cheapo); many people on TV forums reporting that it is a dud too. Luckily for now the original style is still available where stock remains. I would try converting a new one to C120 to see if it's just the feed that's poor (I have a hunch it is illuminating far too much, on my Triax dish I had to run it pushed as far in as it would go) or if it's the actual LNB... but they have a square waveguide that complicates matters somewhat!
Charlie |
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On 24/11/2022 13:44, geojohnt via groups.io wrote:
Charlie, David and All,John, Looking at this morning's plot, if someone said the red (vertical) was a little lower in frequency than the cyan (horizontal) I would not immediately disbelieve them. I understand the transponders are analog ones (not digital) I guess it would be easy to tweak the uplinks by +/- 0.5 MHz without causing major problems. Looking on the spectrum analyser at the output of a TBS 5925 tuned to 11263 MHz, it's really difficult to judge, but I /estimate/ that the V transponder is a couple of hundred kHz higher in frequency than the H, so the opposite of what I saw on the CrazyScan plot. I did notice that V is not pure 16APSK2/3 but appears to switche (like HVS-1/BAS) to 8PSK3/5 - perhaps during gaps in the data.... Cheers, David -- SatSignal Software - Quality software for you Web: https://www.satsignal.eu Email: david-taylor@... Twitter: @gm8arv 
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