Question Coaxial cable aerial issue

the groundsman

Established Member
I follow the Hifi forums on here and as people are helpful there with dumb questions I'm hoping for the same patience here. I

I have 2 TV aerials one directly above of another on a bar in the loft. I didn't erect them they were here when I bought the house. One feeds the main TV in the living room and has worked just fine for years ( decades ) in fact. We can almost see the transmitter from the house and the signal strength is good. When I bought a new TV I wanted to re-purpose the old one in an upstairs bedroom.

I have run coaxial cable from the TV via a plastic conduit into the loft and wired into the spare aerial. Connecting the copper wire sticking out of the plastic sleeve to one terminal and twisting the whispy copper outer part to the other.

On the TV the picture is pixelated and the sound choppy. The TV says the signal strength is good but the quality moves between 75% and 50%.

I have a Humax PVR in there too and when I connect that the picture is OK, So I watch the TV using that connected to the TV with a Scart cable.

Any ideas what might be wrong here. Could the aerial be defective in some way ( its just a lump of metal really isn't it so I Thought that unlikely)
Last edited:


Prominent Member
9 decades? 90 years? That's before TV broadcasts began in 1936? What sort of aerials are these? Please describe them if you do not know the technical descriptions

the groundsman

Established Member
Typo should have been in brackets *(Decades) now corrected :)

They look a bit like this


  • Screenshot 2020-09-16 174208.jpg
    Screenshot 2020-09-16 174208.jpg
    16.3 KB · Views: 59


Distinguished Member
It might be overload (too much signal) the varying quality with high signal is a classic symptom.

An attenuator is required between the aerial and TV.
Disconnect the aerial cable from the aerial. Strip it back so the inner and braid are each around 4 inches long and form into a T-shape. That will act as a crude dipole aerial. This is the one behind my upstairs bedroom TV. It's based on the one made by a colleague when we moved into White City.
UHF dipole.jpg

Does the TV now work OK?

Aerials must be spaced at least a metre apart. Otherwise the bits of metal can interact and cause all sorts of problems.
Contract aerials (as pictured) are the worst aerials known to man (after set top room aerials).


In memoriam
Cheap flimsy contract aerials, Replace with one of these. You will need to fit a screw on f connector to the the coax and ideally use double screened coax cable like Webro WF100

Amazon product

You might need a cheap plug in signal attenuator.


Distinguished Member
@the groundsman I'd really not recommend spending money on a new aerial.

While contract aerials are a variable feast they work OK for an enormous number of people and the main one has done so for decades for you, so no need to replace... Just use it for both TVs:

The one that feeds downstairs can be passively split 2 ways losing a tad over half the signal to both (-4dB) which might well be enough to resolve the problem on the bedroom set.

(Assuming the lounge is 10 metres of cable longer than the bedroom cable the loss in that would be around 2.5 to 3 dB... and the bedroom TV worked fine with that arrangement before being relocated.)

It will just need a suitable metal bodied splitter and the connection plugs made off properly.

Splitter - internal F connector type c/w plugs - A.T.V. Poles, Brackets, Clamps & Aerials if the cables you have are suitable or Splitter - internal 2 way CoAx type - A.T.V. Poles, Brackets, Clamps & Aerials using Belling Lee TV plugs (NB the input from the aerial is a male plug so will need a cable socket or female-to-female back to back joiner with a cabled plug.)

Wiring up plugs, aerials and wall plates - A.T.V. Poles, Brackets, Clamps & Aerials is a useful read.
Last edited:

the groundsman

Established Member
Thank you for all this information.

Trouble is I'm too scared to mess with the main TV. If that didn't work I think the sentence might be crucifixion. I know you will say it's fool proof, but just can't take the risk :)

To be honest I only started thinking about this again when I had an aerial installer guy out to fit a bird guard to the chimney at the start of the week. I have an FM aerial on the chimney which is redundant but the wiring it feeds are for conveniently situated face plates. I asked him about replacing the FM with a TV aerial and his advice was to split the loft aerials and dispense with the outside stuff. He said he do it all for me for £50; quite a bargain I thought. I can watch TV fine via the humax PVR but only in SD, so would quite like an HD set top box.

So if I got one of these Attenuator

and a couple of these F Plug

I might be home and dry for less than £10?.

Job for tomorrow is to try the the crude Dipole approach.

I really appreciate your help btw.


Distinguished Member
An aerial installer who sidelines in roofing work is a new one one me. My bird guard was installed by a local chimney sweep.

:devil: Man with van with ladders (and stetson?) :devil:

PROception F-Plug CU/CU CT100 Cable are the F-plugs I'd probably choose over your link - they look to have a bigger 'nut' like the ones Justin at ATV aerials sells. But screw on F-plugs do need to match the cable diameter so double-check that!

the groundsman

Established Member
By way of update. I tried the variable attenuator thing, but it didn't appear to make any difference what so ever. I think If I'm serious I'll have to get a professional in.


Distinguished Member
Lets get methodical.

Humax PVR (exact model number?): that works well via the second contract aerial and cable with no breakup.
Check all multiplex frequencies tuned on it and report the signal level and quality readings.

TV connected via the RF passthrough from the PVR:
that is an amplified splitter plus perhaps an analogue modulator inside? - if so that RF out frequency may need moving away from a transmitter multiplex frequency that it is causing interference to?

Possible that the Humax amplification overloads the TV?:
Try the TV tuner direct fed from the aerial.
Is that OK? Use the TV meter to report signal level and quality on each received / tuned multiplex.
If yes then use a passive 2-way splitter to feed both the TV and Humax 'direct'?


Distinguished Member
Not entirely clear from the OP & I've only skimmed the replies, but are getting the issue with the aerial directly connected to the TV or through the Humax with the Humax in standby? Humax PVRs generally have a setting to allow passthrough of the signal in standby (or not), tied to a low power standby mode. By default the low power option is often "on", which means passthrough is disabled.

the groundsman

Established Member
OK - this is the weirdest thing.

I just turned the TV on to get the details @Rodders53 was asking about and the picture and sound were perfect on all channels. I tried the aerial in the PVR (Humax 9150T) with pass through and also directly in the TV and the results are all fine. So what has changed? I then remembered I moved my Google Chromecast dongle last week as i needed it on my living room TV. It's been plugged in there all week.

When I reconnect the Chromecast dongle to either of the HDMI sockets the TV picture is distorted again. Even just having the Chromecast powered at the rear of the TV (not even plugged in to the HDMI) causes the issue. IT caused no issues on my living room TV.

I am perplexed.


Outstanding Member
Anything connected by HDMI cable to a TV can cause interference and block certain channels.
The HDMI cable radiates spurious RF.
Try an HDMI extender cable on your Chromecast and keep it as far apart as possible from the aerial cable.


Distinguished Member
Better screened hdmi lead (not possible with Chromecast TV unless using an extender lead).
Proximity to the aerial cable (also difficult to move without an extender).
Better screened aerial cable (try other fly leads you have to see if it helps) or remake any TV plugs if loose or the screen isn't well clamped it will let in interference.

Try not using a TV USB port to power the Chromecast but a separate USB charger-type supply? (Or vice versa)?

At least you've discovered the cause of your problems! :clap:


Novice Member
Hello sorry if this is slightly off topic and a dumb newbie question. But I want run my aerial on my existing virgin media cable to the TV which is at the other side of the room. Can I just unplug the coax cable that runs to my TIVo 6 from the splitter and attach the aerial cable to it and plug it into my Panasonic TV to get all the free channels. I will clearly need to bring the cable into the home.Or does it need to be a particular type of cable. I tried to follow the debate above but got lost in what I might need .


The latest video from AVForums

Samsung & LG UK TV Prices 2023; Amazon Fire TV Cube; Calibration Tools of the Trade + AV news
Subscribe to our YouTube channel
Support AVForums with Patreon

Top Bottom