Even if it’s been split already?
You raise a valid point; several in fact from previous posts.
Even where you have strong/good signal, the total number of splits that can be made with either passive or powered splitters is limited, but for different reasons.
With passive splitters, the limit is the power of the signal direct from the aerial.
Each time the signal is split two ways, the power drops by half. Using a 4-way splitter is very much like cascading an extra 2-way splitter on each leg of the a previous two-way split. The signal is halved again: 100% goes to 50% and then drops to 25% on each of the four legs. An 8-way splitter reduces each leg by half again. Now you have 12.5% of the original signal on each of the eight outputs, and this is regardless of whether there's a TV hanging off the socket or not.
Percentages (or fractions) makes the relative signal levels easy to get our heads around, but isn't so useful when trying to sum the effects of all the various losses and gains in an aerial system. Decibels (dB) is more useful.
Every time the signal is halved, the dB level drops by 3.5. Halving it again is another 3.5dB reduction. The total is 7dB. That would be the effect of a 4-way splitter. Halving again gives a total reduction of 10.5dB which is what you get with an 8-way splitter.
Talking about losses and gains in dB is useful because it's easier to work out the cumulative effect of all the devices in the signal chain. Splitters, amps, filters, attenuators etc all have their losses or gains quoted in dB. Even cable -
or the decent stuff at least - has its loss quoted. Webro WF100 (good cable) has a loss of 0.15dB per metre, so 10 mtrs knocks 1.5dB off the signal's power. Cheap aerial cable can be way more lossy than that.
The point of knowing how much the aerial system will lose is that it becomes possible to work out whether there's enough signal to stand up to splitting, or, how much signal is needed from the aerial in order to accommodate some level of splitting. However, you need a reliable way of measuring the signal level directly at the aerial.
For the tuning and reception in a Freeview TV to work properly, it's recommended that the signal level at the TV's aerial input is somewhere in the region of 50-65dBuV. Working back then towards the aerial, and including 20 mtrs of cable and a single 8-way passive splitter, we'd have 3dB for cable losses and 10dB for the splitter. That's a total of 13dB. Add that to what the TV needs, then at the aerial we would need it to produce 63-78 dB of signal. In a strong signal area with a good aerial then that would be achievable.
Your system already has a splitter on the downlead from this difficult-to-access aerial. If you're thinking of splitting one of the legs, then you're working with as little as 25% of the original signal (-7dB), and so splitting that again another 4-ways (because most stores sell splitters in 2-way, 4-way and 8-way steps), then the splitter losses alone will be 14dB. You then have the cable run losses plus 1~1.5dB if you're using wall plates.
I mentioned that cheap/poor quality coax can be very lossy. Well, if you want a real horror story then the measured losses from those pre-packed aerial fly leads are a complete nightmare. Make your own fly leads from good coax. It's no more expensive, and you'll avoid a lot of the signal problems that plague folk using those poorly-shielded leads.
The bottom line is that splitting like this is very likely to put too much of a loss on the signal for the new TV points. Your plan for a second aerial dedicated to those points is the way that I would go. This, or put in a powered splitter up at the old aerial, but that just feels like the wrong course of action given what's happening with the retunes to accommodate the 4G/5G sell-offs.
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