Signal Attenuator location

mrwrighty

Standard Member
I currently have a loft aerial feeding 5 TV's. I live high up on a hill and have virtually line of site the the Transmitter which is about 8 miles away. Originally I had an active splitter powered via one of the Coax leads but was getting pixelation across a couple of the TV's, namely a Panasonic and an LG 24". Both of which actually use the same base TV platform (Not that that matters, but noticed different manufacturers but effectively the same TV). I removed the Active splitter and put in a passive splitter as I believed the signal was too string. Generally this did improve things, but the Panasonics and LG still suffer the odd pixelation so I'm thinking the signal is still too strong.

I'm thinking of buying a adjustable attenuator. All connections are F Type at the aerial and passive splitter.

Can I install the Attenuator between the aerial and the splitter thus reducing the signal strength across the board? Would this have the desired affect?

Thanks.
 

Rodders53

Distinguished Member
In short yes.
Aerial, attenuator, splitter (-4dB, 2 way: -8dB 4 way, -12dB 8 ways), TVs.

In long:
With a passive 4-way (-8dB loss per way) and a 2-way on one of those outputs (-12dB total on those two) to feed 5 TVs, I wonder why you need more attenuation.

Lets assume your amp had a low +8dB gain. By changing from amp to passive that's -16dB or -20dB signal level. That the sets are still exhibiting issues (and the other three TVs not??) suggests something else to me.

What signal strength and quality readouts on the various TVs for all received muxes?

Check for potential mobile phone interference at Restore TV | TV Signal Interference | TV Filters

Approx location (nearby postcode of shop, pub etc.,.) to allow signal level prediction?

Check out fly leads, hand made connectors, hdmi cables near the aerial leads on affected sets. Swap out with alternative cables. Check if wallplates are screened or unscreened (bypass/remove any unscreened ones?)
 

mrwrighty

Standard Member
Thanks @Rodders53.

I probably over did the aerial in the loft. I got it cheap and I think a High Gain type which is probably overkill given the location of the transmitter. Not all TV's are running together, perhaps 1 or 2 at most, depends which room we are in at the time. The Main TV downstairs is on a separate aerial from the rest. I have replaced cables made by me with ready made cables and also tested my cables with a meter to ensure there is no short across the copper and all are good. TV sockets are shielded. Pixelation comes and goes which I think is atmospheric rather than physical connections. Bear in mind this only affects 2 of the 5 TV's as I mentioned in my OP, so they are likely more sensitive to the higher signal strength. I've ordered a variable attenuator so will see how that goes.

Thanks for your reply.
 

Rodders53

Distinguished Member
Do your predictions:
Detailed transmitter information for industry professionals for interference predictions
wolfbane.net for signal (field) strength. Reduce height to 8 metres as in the loft not outside and report the numbers (and if starred).

Lofts: materials attenuate the signal cf outside by about 10dB --- aerial gains are often quoted as dBi rather than dBd to give a bigger number but rarely do you get more than 12dBd gain. So basically make up for the roof materials losses. ATV aerial gain tests : all the gain curves - A.T.V. Poles, Brackets, Clamps & Aerials

So were at the 4-way splitter and a -16dB gain difference with amp/without. T
But the S and Q numbers from the affected TVs and another TV set for comparison might give some better clues (confirm or refute)?

Try the TVs on the main TV aerial to see if they react the same way? Is that external? What type/gain?

Which TV channels are affected - it would be most unlikely to be all if an atmospheric issue.
What transmitter BTW?
 

mrwrighty

Standard Member
Main TV Aerial is external. Transmitter is Malvern, line of site approx 8 miles and we are on side of hill facing the transmitter so no access to an alternative. Malvern is linked to Sutton Coldfield both of which are listed as poor, however I'm getting all channels include HD, although I did struggle with one TV before I removed the Active splitter.
 

Rodders53

Distinguished Member
Malvern is one of the smaller 81 or so 'Main' transmitters (duplicated kit, 6 mux, line fed).

Only 400 Watts erp so 8 miles away isn't going to be overload without massive amplification in use.
Field would be circa 46 dBuV/m at 8 miles with clear line of sight. So I'm unsure how you are receiving from it with that much attenuation and a loft aerial.

DTV Receivers require 45-65 dBuV to work well.

Malvern: Cross-rods would be Vertical along the horizontal boom arm.
What frequencies are tuned?
Malvern is 41, 44, 47, 29, 31, 37.

Those TV meter numbers would be very illuminating?
 

mrwrighty

Standard Member
What do you mean by TV meter numbers, sorry for my ignorance. DIY'er here so not use to the terminology.

External Aerial is set with rods vertical.

Screenshot 2022-04-26 at 14.17.21.png


Loft Aerial is similar to set vertical.

Screenshot 2022-04-26 at 14.19.00.png
 

The latest video from AVForums

Samsung S95B QD OLED Review - A Quantum Leap for OLED!
Subscribe to our YouTube channel
Support AVForums with Patreon

Top Bottom