3dB signal at LNB, enough for multiswitch?

[OldBen]

Right, still plodding away at my new solution since I moved months ago

Have a TD110 dish I plan to use for 28.5E, 23.5E, 19E, 13E, its been on patio stand out back for a few months as overkill for 28.5 with a single feed to freesat TV (no dropout in bad weather ;))

FINALLY got around to some testing with 23.5, as Astra A in particular 12525V for CSLink is fringe for my location (close to Reading) and using the Satlook Lite meter I get a reading of 3dB at the LNB. I realise this is subjective, but for comparison the main transponder one of the 3B ones on the euro beam programmed into the meter reads 11dB. LNB is Inverto Black Ultra single.

Now since my technomate died and I have been two tight to buy a new receiver until I have dish sorted (catch 22) I only had the TV for this test, but with my current cludge cabling for 28.2 which is 14m or so cable to loft and about 9 back down again (joined with screw f plugs in loft) it can receive the stations on this TP ok using the TV's very limited scan.

What I would ideally like to do is replace the single for a quattro and chuck it through a multiswitch in the loft. What I am struggling to understand is if I have enough source signal to do this, or the loss in the switch will kill my reception? Receiver with multiswitch would be a VU+ Duo most likely (TV only for freesat).

Anyone give me their experience of what 3dB plus 14m cable before switch (which I am assuming amps signal internally, so its signal at switch I am interested in) would be workable? looks borderline based on TV display of signal quality?

If not, would diseqc switch be likely to also loose too much to be workable as a solution?

I could dedicate a tuner on the Duo to 23.5, but that doesn't fit with my overall plan for world domination with an over-engineered solution ;)

 

[Huevos]

using the Satlook Lite meter I get a reading of 3dB at the LNB. I realise this is subjective, but for comparison the main transponder one of the 3B ones on the euro beam programmed into the meter reads 11dB. LNB is Inverto Black Ultra single.[...] Anyone give me their experience of what 3dB plus 14m cable before switch (which I am assuming amps signal internally, so its signal at switch I am interested in) would be workable? looks borderline based on TV display of signal quality?

3dB what? SNR? MER? C/N? Gross signal? dBuV? If it is 3dB MER or signal to noise it is well below the reception point.

 

[Robbo]

Yep, 3 dB signal level is meaningless. I suggest you look up the loss through the switch you intend to use, and calculate additional cable losses, then put an attenuator of equal value in there and see if your receiver still works, should give an indication that a multiswitch would work, as long as your SNR is not compromised.

The signal level on receiver looks quite high on the scale. Signal quality is not necessarily affected by IF losses, as long as they are not too much.

 

[OldBen]

Sorry, see you can tell I am not a pro here ;) its 3.1dB SNR indicated on the meter. The BER is 1.3E^-05. That's on the meter, and of course that may differ between meters? By comparison offset 28.2E is 8dB or so and the transponder programmed into the meter on 23.5 (which is focus) of 11973V is 11dB.

3.1dB can't be below reception point, as even after the cable run the TV can pick up the signal ok and I suspect its tuner is a lot weaker than a dedicated receiver as its just designed for freesat on 28.2. In fact the meter can lock the transponder down to an indicated 1.1 or 1.2dB so I would strongly suspect the SNR calibration of the meter is out versus your expectations Huevos.

Some of the switches I have been looking at 8 or 12 output switches and they typically quote 0dB insertion, but that does not seem realistic to me? Others seem to quote 2.5-3dB loss.

The previous screenshot was from the TV, I strongly suspect its not the last word in tuner sensitivity and that a dedicated receiver will be stronger. I was surprised Robbo how strong it shows the signal. Attached is the diag screen from the TV on a clear channel (will be getting genuine sub card once I am sure reception will be consistent).

(EDIT: Note BER is 5^-05 in the screenshot, and this is after cable run to loft and back & join)

Now you mention it I do have some attenuators in the box'o'bits I will have to check if they are VHF only or work at 2Ghz and perhaps try those inline.

The reason for the question is of course I don't want to buy a quattro's only to find the signal is too weak and I need quads and diseqc switching for main PVR, mind you they are 2-3dB loss spec sheets say!

Sounds like there is no more theory, just experimentation!

 

[Huevos]

its 3.1dB SNR indicated on the meter.

If so there is something wrong with the calibration of the meter. If it is a 2/3 fec transponder it would need at least 6dB SNR to get lock. The following is a quote from an Emitor manual: SNR. The signal/noise ratio should be as high as possible. A good signal should have at least 8.0 dB S/N-ratio.

 

[OldBen]

FEC is 3/4 on 12525V on 23.5 if that makes a difference?

No mention of level in Satlook Lite manual, just that they should be at maximum. Don't know anyone else locally with a decent meter or I would be able to compare. Did a friends dish with him recently and his Quattro on 28.2 was showing about 7.8db, that was with TP 11224V FEC 2/3.

Meter uses 11973V with FEC 5/6 on 23.5 (showing 11dB SNR) and the programmed 12525V FEC 3/4 I entered for CSlink TP was showing 3.1dB.

So what I have learned so far today is... meter SNR is incorrect, and I can't use that for calculating losses!

 

[satelliteman]

Yes 3.1dB S/N is way below any signal lock.

 

[ralphmagno]

hello,
is this a dish with a motor?
if you have a motor why have a multiswitch.
unless you are running several sat boxes in the house..most small multiswitches have a small loss.
but this is not enough to cause a problem.
if you are looking on a satellite receiver display those are not precise as a good tester.
a satellite signal transmitted from space looses about 120 db traveling from the satellite to your dish.
if you have say a 1.2 meter dish it has a gain of 42 db and the lnb has a gain of 54 to 60 db as well.
most satellite tuners will work on a signal of -30 to - 60 db.
if the multiswitch is giving you problems that it may have a defect.
ralph

 

[OldBen]

Hi Ralph, dish has gain of 40dB, LNB spec says min gain of 60dB, as per original post I am installing new switched system, dish with motor has been retired when I moved house. Reception is borderline for my location, I was wondering how much loss people expect through a switch.

 

[ralphmagno]

hello,
i don't think for than 1 db insertion loss.
and being your line is short and you have a 110 cm dish it should be ok.
if you want to mesure something pick a statellite and a frequency.
then put in the switch and use the same frequency same satellite.
ralph

 

[OldBen]

Thanks Ralph and others.

Going to buy a switch (might pick one up cheap on eBay for initial testing!) and give it a try.

 

[PaulR]

Just applying common sense and forgetting figures, a 110cm dish with an offset feed for 28E (what is the prime focus of the dish?) in the UK is going to provide plenty of latitude for signal loss in cable and multiswitch.

The rule of thumb is to go up a size of dish to provide extra signal for the increased noise floor, so a 60cm, or 80cm in the north, with a quattro is the usual solution for a multiswitch.

 

[satelliteman]

I was wondering how much loss people expect through a switch.

This will depend on the switch, some are active, some passive. A multiswitch will quote any loss or gain in dBuV.

 

[Huevos]

dish has gain of 40dB, LNB spec says min gain of 60dB

This is a common misunderstanding of digital systems. With digital the important thing is signal to noise ratio, not insertion loss. Putting a switch inline will cause a small insertion loss, just the same as adding a few meters of cable, but will make no difference to signal to noise ratio.

Common wisdom of going to the next dish size up comes from the analogue days where gross signal level was the all important factor.

 

[OldBen]

Huevos, I think you hit the nail on the head. If you look at the screenshot there is plenty of signal, its just poor quality (low SNR). If the switch drops the level slightly as long as the signal is there out of the noise I should be OK.

@satelliteman, looking at powered one (rather than line/drop fed from launch amp) as its just small domestic with short runs, so perhaps that's why it quote 0dB insertion loss as its active.

@PaulR 23.5E is prime focus as its borderline for TD110 on 12525V, everyone told me 1.2M is needed, but with Black Ultra and very careful alignment (dish is ground level, so opportunity to tweak all of the dish construction to max signal!) it seems to be fine. I figured 28.5/19/13 offset on a TD110 would be peace of cake (yet to try 13, 28 easy).

 

[satelliteman]

@satelliteman, looking at powered one (rather than line/drop fed from launch amp) as its just small domestic with short runs, so perhaps that's why it quote 0dB insertion loss as its active.

Yes, will be active. Some active switches do have a gain.