New LG OLED TV picture breakup on Freq Channel 23


Standard Member
Looking for some help with the following;

Have just purchased an LG OLED55C9PLA (2019) OLED HDR 4K Ultra HD Smart TV, 55" with Freeview Play/Freesat HD. It is configured to use Freeview.
The aerial configuration is;
2 external digital aerials on outside of house. One pointing at Mendip (West) and the other pointing at Pontypool (Wales)
Connections from each pass through a diplexer and input into amplifier located in the attic. Outputs from amplifier via coax to other TV outlets located around the house.

I am experiencing picture/sound breakup on the new LG TV on PSB1 (Frequency channel 23 – 490.2 Mhz). This has been manually tuned. If I plug another TV into the same wall socket, I get no issues with channel 23. Other TVs around the house (connected as outputs to the amplifier) have no issues with BBC Wales – SD (frequency channel 23 - Pontypool transmitter)
No issues with other PSB Frequency channels from Pontypool
PSB 3 (Frequency channel 29 - 538.2 Mhz) and PSB 2 (Frequency channel 26 – 514.2 Mhz) on any TV including the new LG one.
Have noticed that the signal strength on the new LG TV is at 100% when on channel 23. The signal quality is all over the place – hence it looks like interference from somewhere is affecting it on this TV only!
Thought the problem might have been down to over amplification so took the amplifier in the attic out of the equation. (Basically, took the input into the amplifier and joined it directly to the coax in the living room). This made no difference – still had picture break up.
Could this be the TV?
It was purchased from John Lewis and they won’t replace as I have had it over 30 days.
I have read about 4G interference? The amplifier I have has no filter but still getting issue with no amplifier in place.
I have removed all HDMI cables from the new LG TV – made no difference



Distinguished Member
The classic description of too much signal in to a TV tuner. 100% signal and fluctuating quality.

But you have tied to eliminate that as a cause by bypassing the amplified splitter.
Did you measure the signal/quality when direct connected to the (combined two) antenna? If not, repeat that measurement - it is possible that the set is still receiving too much signal for its' tuner.

A simple attenuator could cure that? Splitters, amps and diplexers - A.T.V. Poles, Brackets, Clamps & Aerials You must, however, ensure that all other wanted mulutiplex frequencies (muxes) are received OK still (use the metering to check levels of each mux).

Pontypool and Mendip with digital is not simple to combine properly (i.e. using filtered combiners). {Although for analogue and post-DSO for a time that was possible - Ponty being group A and Mendip group C/D.}

Using a wideband combiner will likely result in unusual effects of frequency selective cancellation and reinforcement between the two aerials - one horizontal, the other vertical - for the two transmitters. This may explain an unusually high level for ch23 that is upsetting the TV?

If the combiner is also in the loft it may be worth experimenting with one aerial at a time connected to the LG?

4G interference is well above the highest frequencies in your location and would not affect ch23 only, nor only one TV in the home.
Hdmi cables need disconnecting at BOTH ends if interference is suspected; not just the one on the TV.

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