Loft aerial shorting?

[DaveK95]

Hello all,

So my TV signal has been terrible for the last couple of days.

I decided to check all the cables / connectors using a multimeter on continuity, making sure the shield isn't touching the copper core. They were all failing detecting a short.

I've traced it back into the lofts aerial and removed the cable tested it then and it was fine. So I put the cable back in and it's now shorting again.

I took the cable out again and tested the terminal that holds the copper core, cable clamp that holds the cable / shield, it's showing a short.

So probably a dumb question but before I buy a new areial, are these connectors in the attached photo meant to be connecting? My understanding is that having them touching would cause issues?

Any help would be much appreciated 

Thanks! 

 

[ProDave]

Yes quite normal.  Just because they are a short circuit at DC does not mean they are a short at RF frequencies.

So you have tested that the coax is open circuit on it's own. that is good,

Now check that the coax, at the tv, becomes an aparent short circuit when you re connect the aerial.

Are there any aerial amplifiers etc anywhere? they are prone to failure.

 

[Evans Electric]

That would be my understanding too.    The clamp with  two screws fits onto the braid  ...the centre core  in the terminal  , they don't touch  as far as I know . 

The clamp may be connected to that large section of aerial   and the core to the fins ,  I don't really know .  

 

[kerching]

Aerials are a total black art to me, sorry

back in the day my mate customised his escort van....porthole side windows, awful paint job, massive CB rig with associated antenna 

anyway, magnetic mount failed and it fell off the van roof   Ended up in A&E with a very nasty flesh wound,  Consultant reckoned it was worst case of Van Aerial disease he had ever seen!

eye thank yowe!

 

[roys]

Nice one Kerch 

 

[DaveK95]

So done some more research, apparently lots of aerials will come up as they're shorting under a continuity test. So I scrapped that idea and went back down the cables, until I found a 3 way splitter that had corroded nicely. I took it out and just connected the cable straight to the aerial and boom it's working! It's even now picking up HD channels

Thanks for the help everyone 

 

[Geoff1946]

The receiving element is that loop of aluminium the junction box is mounted on. Think of the loop aerials which used to come on old portable TVs;  - It's just that located remotely.  All the other bits of the toast rack are either reflectors or directors and work magic on the airwaves which few can understand, but make it directional.

Something to bear in mind is that the co-ax deteriorates with age, even if it looks OK. It's semi-air-spaced and gradual moisture ingress into the air spaces make it progressively more lossy. Marginal signal strength can sometimes be fixed with a new length of decent quality cable.

 

[Evans Electric]

So done some more research, apparently lots of aerials will come up as they're shorting under a continuity test. So I scrapped that idea and went back down the cables, until I found a 3 way splitter that had corroded nicely. I took it out and just connected the cable straight to the aerial and boom it's working! It's even now picking up HD channels

Thanks for the help everyone 

Great to see problem sorted