Well… you have to connect something to it or it’s just a splitter sitting on a shelf! 
Coax in… and both outputs get dropped about 3.5db. So whatever you connect to either of those (or both) has the lower db. You can use it like an attenuator to test, but if the second “out” port is unused you should stick a terminator on it… eventually… should be fine for testing purposes though
My advice from 3,000 miles away:
After running a TVFool reception report, pay attention to the NM (noise margin) number reported for the channels that you’re interested in receiving. That value MUST be over “zero” for reception, and for reliable reception, should be above +15.
Build an insertion loss budget worksheet. Essentially, calculate the amount of signal loss (in dB) along the path from your antenna to the tuner. This should include:
a.)the loss at the balun (matching transformer)
b.)the loss from the coax cables (there are tables on-line that will show you the dB loss per 100 ft of RG-6) which include the down-lead from the antenna to the pre-amp, the drops from the pre-amp to the tuner
c.)the insertion loss at each splitter port in the path of the signal (that is, the loss through one port of the splitter- although a three way splitter will have a higher loss at each port than a two way splitter
d.) the insertion loss from any barrel connectors, cable joiners, or wall plugs (typically -0.5 dB each)
e.) the insertion loss from any attenuators installed
f.) insertion losses from lightning arrestors installed
g.)Noise factor created by the pre-amp and/or distribution amplifier
You should also have at hand
h.) the gain, at frequency, from the antenna
i.) gains from pre-amplifier and/or distribution amplifier
3.) With those figures at hand, plug them into the spreadsheet posted on this link:
Once you have the Net Margin, evaluate the result, and play some what-if scenarios, removing the preamp from the model, adding attenuators, etc. A noise margin number over 70dB is significantly overloaded, and 60-70dB are possible overload candidates. Net Noise margins from 40-60 dB will typically not need amplification.
It’s just my perspective, but a +30 dB preamp invites significant signal overload.
Finally, take a look at your coax plant. Terminate all open ports. Torque down coax connectors on non-electronic devices to 20 inch-pounds (10 inch-pounds for connections to set top boxes, Tablo DVR’s, televisions, etc). Replace any coax where the shielding is split or exposed. Waterproof outdoor connections to the best of your ability. All of that is just best practice for creating reliable reception.
As a very rough, but still close estimate, I come up with a Net NF of 24db w=for WESH, which is the weaker of the major channels at 15.1 NM per tvfool.
It’s just as important, if not more so, to check the strongest station in the antenna beam direction, as that’s where an overload condition is more likely to occur. Spurious secondary signals from an overload can cause problems not just with the desired channel, but peripheral station reception problems as well, dependent upon the selectivity/sensitivity of the tuner.
Removing the preamp gain and associated NF leaves a Net Noise Margin of 13 dB (NM(air) + Antenna Gain - Distribution Losses - Tuner NF). That’s on the borderline of reliable, but also shows that a 30 dB gain preamp is overkill for even the weakest station. A smaller distribution amp (carefully selected to overcome downstream loss) would be more suitable in this environment.
I guess it depends on what we consider is the weakest signal. The strongest signal coming from the direction my antenna is pointing is NM=18.9, which I do not include in my desired channels; I’m sure that doesn’t matter though that I do not include it.
The highest NM for a channel I include is FOX, Channel 35.1, at NM=16. Here are the results from tvfool:
Is it not possible to offset the preamp with attenuators and get a good signal and good reception?
I have a 3-db and 10-db attached to my tablo right now, and a 6-db still to be delivered.
It is easier for me to add attenuators than it is to replace my preamp.
My confidence in the results from tvfool are not very high right now. I am not even seeing ABC, channel 9.1 WFTV, in the results for my address. I live in a very new area, my house was only completed last September, so I wonder if it is even using the correct location?
I don’t think tv fool is correct. They have me mostly in gray area, but I am not tech enough to figure it out. also want to let you know WESH is saying there doing ota antenna changes on June 10th. We will need to rescan, there site says.I hope its for the better, don’t know.
Thanks Jim! I saw that as well and they actually announced it this morning when I was watching their local news. We can sure hope they make a change that works in our favor.
Not to be vague or misleading, but the answer to using attenuators and the preamp is “yes and no.” The amplifier is making up for the downstream loss- in other words, the distribution losses and insertion (splitter) losses are cancelled out by the amplifier. If you add the attenuation loss into the distribution loss figure in your worksheet (from 7 to 20) you’ll note that the Net NM doesn’t change.
Given the TVfool report, I don’t think overload is necessarily the issue, assuming your loss budget is correct. The improvement you observed after installing the attenuators may be coincidental.
You may have done so and reported earlier in this very long thread, but can you hook your antenna directly to a TV that has a digital signal monitor? I’m not so interested in the numbers (although the installation/removal of the attenuators would be demonstrated there). I’d be more interested if the signal strength numbers are bouncing around at the time when you are observing macro-blocking/pixellation. A rapid bounce in those numbers are typical for a local multi-path condition. Given the low noise margins to begin with, a change in the received signal strength before it hits your antenna could drive that below the margins for consistent reception.
Unfortunately I don’t see where my TV has any sort of signal meter. I have a Sony XBR-65x930d, one of the newer 4K TVs. I am surprised that it doesn’t.
I’m going to go out on a limb and say 99% of TVs don’t have a live “signal meter” and work similarly to Tablo though their scan might be quite a bit faster. But usually after doing a TV scan, I have to go in and edit/delete channels (again). My own observations over multiple TV brands.
That is to say, feel free to recommend the TV that has a live signal meter.
My LG SJ8500 has an active meter. I can move my antenna position and the signal strength readout will change.
I can only dream. My channel scan is fairly rudimentary. I guess they expect more people to stream or use cable/satellite? I’m actually kind of surprised as Sony “used” to be one of the better brands that you would see something like a live signal meter.
So I guess I will pretty much have to feel my way around in the dark and try and resolve through trial and error. Hoping also that there is no major fluctuations going on…
My preamp is way up on the antenna tower, why it is non-trivial for me to replace. The attenuators are both connected directly to the Tablo and the antenna cable connected to them. So the attenuators are last thing going into the Tablo.
Tablo support monitored my signals last week and said most of my channels were at 100, and that means they could be 100 or something greater than 100. FOX, channel 35, he said was definitely over-tuned.
If the attenuators are helping, keep going. Doesn’t make sense to me that they should, but I could be missing something.
I hear you on the mast mounted equipment- I have a six foot mast on my roof, so no real issues for me, save getting up on the roof and not falling off.
I have a very old 25" Sony XBR (from like 2004) that has a live scan meter. Surprised that didn’t carry forward, but to your point, I guess they figure most folks weren’t bothering with OTA reception. As Vizio demonstrated a couple of years ago, the set has to have a tuner in order to be marketed as a “television” in the US.
My LG (one of those cheapo OLED ones) I don’t has this.
I have 2 Samsungs, an older Magnavox, and a Sansui. They all have live signal monitor. You may have it but it’s buried in a menu somewhere
I have a samsung and a magnavox, they also have signal meters. Have to change source on remote to antenna.
