Well that was a fun exercise...
Some 18 years ago I put up a new aerial (group B with some bits hacked off on Bill's instructions to tune it to act more like a group E). Decent Proception masthead amp and power supply, 5 way inductive splitter inside, and then runs off to various TV points. Pointed at Sudbury some 35 miles away.
It has worked flawlessly ever since, not even phased by the various bouts of Freeview channel shifting. Art least, that was until a couple of days ago. Mother's TV was glitching and dropping out on most channels. So fearing some woe had befallen the aerial or a co-ax, I got out Terry, my trusty UHF signal meter, and plugged it into the drop wire from the aerial, turned on the meter's 12V power supply, and low and behold, six muxes, all at a solid 72 to 84dB, and all showing a "Pass" quality.
So rejigged to allow the normal PSU to feed the masthead amp and measured again - same result. Connected the splitter up and looked at the output. Again a fine display of passes and levels showing 67 - 76 dB. Seemed pretty reasonable after a 5 way split. Then metered the aerial socket near the TV, again spot on. Plugged it into the TV, glitch city...
Noise getting in? The flylead was a cheap thin premade jobbie. So I made up a nice new one with some WF100 double screened co-ax, and no better. It was beginning to look like it might actually be a tuner fault on the TV. Fortunately there was a spare one that I had recently pulled out of an office prior to a re-furb. So I got that, set it up expecting better results, and nope, exactly the same symptoms. Too much signal? Added a
6dB attenuator inline - nope that was worse.
I was now entering the clutching at straws phase. Could the amp's PSU be injecting noise (18 year old caps and all that)? So I pulled that out looked at its output on the DSO - smooth as a baby's bum.
Scratching my head trying to think what has changed in the last few days? Then it dawned on me that I had finished installing a new wifi access point at the back of the house a few days ago (long way from the TV), however that also supported mesh operation, so I enabled that, and then turned on the 5GHz wifi on the main router (previously I had that turned off since it was tricky to get it to play nice with other 5GHz access points without a mesh capability). So out of curiosity, I turned off the 5GHz network on the main router, and tada! Problem sorted.
Odd it could upset two different sets placed about 6m and a couple of walls away from the router, yet it did not upset the network TV tuner sat 500mm away from the router (which I only thought to check later!) Both oldish LG sets, but of different vintage.