Strange aerial connection problem

Magilla Gorilla

My DTT signal level dropped recently for no apparent reason. I have direct line of sight to Kippure and all connections seem fine etc. After a lot of faffing about and replacing various cables, I have isolated the problem.

When the connector (standard RF Belling Lee) is pushed fully into the TV aerial socket (or at the wall socket end) the signal level drops to about 40% and very high error levels are showing. When I pull out the connector so that it very lightly touches the socket (at either end) the signal level jumps to 75/80% and there is no error reading.

The cable is prone to falling out because it's barely touching. Can anyone explain what is going on and how I might solve it?

The Cush

Magilla Gorilla wrote: »

The cable is prone to falling out because it's barely touching. Can anyone explain what is going on and how I might solve it?

What type of aerial are you using? Is there a masthead amplifier or distribution amp somewhere is the setup?

Magilla Gorilla

Hi Cush.

My set-up is quite complex but I haven't changed anything.

Kathrein VHF and basic Maxview UHF aerials on roof with Triax diplexer. Cable down runs to a mains-powered distribution amp because of cable length due to very big dormer roof (two TVs). Both exiting cables are then diplexed with satellite signals (Global diplexers). Screened high-quality wall plate diplexer to separate tv/sat signal. Finally, UHF/VHF splitter to separate signals to FM tuner/digital TV (i.e. tuner built -in).

If I leave out the TV/FM splitter, problem persists. No problems with satellite at either location. The other TV is fine for DTT signal too, so I'm confused.

The Cush

Magilla Gorilla wrote: »

My set-up is quite complex but I haven't changed anything.

Kathrein VHF and basic Maxview UHF aerials on roof with Triax diplexer. Cable down runs to a mains-powered distribution amp because of cable length due to very big dormer roof (two TVs). Both exiting cables are then diplexed with satellite signals (Global diplexers). Screened high-quality wall plate diplexer to separate tv/sat signal. Finally, UHF/VHF splitter to separate signals to FM tuner/digital TV (i.e. tuner built -in).

If I leave out the TV/FM splitter, problem persists. No problems with satellite at either location. The other TV is fine for DTT signal too, so I'm confused.

Can you bypass the distribution amp to test the signal to the TV? What type of amp are you using and how many outputs?

Magilla Gorilla

Yes, I can do that fairly easily. It has four outputs but I'm using just two. I'll report back.

What are you suspecting? Signal overload?

The Cush

Magilla Gorilla wrote: »

Yes, I can do that fairly easily. It has four outputs but I'm using just two. I'll report back.

What are you suspecting? Signal overload?

Possibily, maybe test the other outputs too. How close are you to the transmitter? Some tuners I believe can be more sensitive than others.

Magilla Gorilla

Hi Cush, if you're still following this, I have an update and thanks for the help so far. I am 35km from Kippure as the crow flies, with clear line of sight.

1. Removing the distribution amp stopped the signal problem at the TV. I put a standard splitter in instead to allow the two TVs to operate. I was able to push the connection in fully and I'm getting a 70% constant signal level.
2. My FM signal went to hell when I did the above. So I put the amp back on the system after the TV/FM diplexer and all is as it should be there.
3. I found an ancient, less powerful Labgear distribution amp. When I put it on the system, the TV signal level dropped to 40% but no errors were showing. This seems to doubly confirm that the original amp was overloading the signal at the TV.

Would you have any idea as to why this has happened? I didn't change anything on the system and I was getting 85% signal previously?

The Cush

Magilla Gorilla wrote: »

Would you have any idea as to why this has happened? I didn't change anything on the system and I was getting 85% signal previously?

I don't know, how close is/was the distribution amp to the problem TV? Difficult to know what the TV % meter readings actually represent in signal strength (dBuV) and quality (BER) without a proper digital meter.

Do you have a separate FM aerial for the FM tuner?

Now that the VHF signal is about to be switched off the VHF aerial and diplexer can be removed and run the UHF aerial feed direct to a splitter (or maybe new distribution amp), any loss through the diplexer will be removed (increased signal strength).

What type of UHF aerial are you using for Kippure - standard contract/grid/other, wideband or grouped. Maybe a slightly higher gain UHF aerial and passive splitter might remove the requirement for a distribution amp as your pretty close to the transmitter.

Magilla Gorilla

TV is maybe 8 metres of cable away- hard to say as it's a dormer so I'm not sure how directly the cable runs to where it comes down the wall.

I'm using the VHF TV aerial for FM and plan to keep it that way so the diplexer has to stay. Would there be any advantage in vertically polarising the aerial for FM afterwards? I can already receive all the local stations (I'm based in mid-Kildare) and occasionally even pick up Shannonside (Athlone) and Southeast (Waterford).

UHF aerial is a contract wideband (Maxview brand). Starting to fall apart a bit so I was thinking of a log periodic to replace it. The splitter I'm using is unpowered- is that the same as "passive"?

Ronnie Raygun

Magilla Gorilla wrote: »

Would there be any advantage in vertically polarising the aerial for FM afterwards?

If you're going to go to that trouble & want to pick up other transmitters, as well as Kippure, just replace it with an FM (band II) dipole rather than using the directional band III aerial.