Co-Channel Interference

Tom Slick

I know analogue TV is dying out (especially the VHF variety) but I have what appears (to my untrained eye) like co-channel,especially on VHF channel F. I could hardly be further away from other Txs using this channel. Can adjacent channels cause this patterning (dark horizontal/diagonal lines) or is it some other source? There are less noticeable patterns also on UHF Divis, but those frequencies are all occupied.(digital,analogue;Divis & Brougher). I know this is all more complex than my understanding.

Local radio broadcasts including mobile phone cells.
Water damage to cables.
Nearby electrical equipment
Wifi gear.

Amongst other things can all cause that.
You need a very good insulated aerial cable if you are experiencing it.

STB

A masthead amp set to high can pull in all sorts of crap, including electrical products.

Badly screened poor cables can do the same with baby alarms, wifi, mobile house phones. Anything really.

It can be as bad as having someone running a 150w FM transmitter next door thats all over the shop.

watty

Never have mast amp more than 3dB higher than loss of cable, connections and splitters after it.

Use double screened Sat cable. Not for low loss, but for isolation. Regular coax can have only 20dB isolation down to 10dB. Sat cable has over 80dB isolation.

If the braid has inner core insulation visible, then it's rubbish. You need foil + solid coverage braid.

Any loose or corroded connections (even on aerial elements) can increase ingress and corrosion can even act as semiconductor mixer such that out of band signals picked up only on aerial are mixed into the band or modulate the desired signal.

Tom Slick

Thanks for all that. Have been meaning to replace some of my less accessible cables. (maybe not today, wet & windy).
BTW have no masthead amps, only old, unscreened diplexer (in loft) and low-gain distribution amp.

deaglan169

hi tom i think from your previous posts that your located in monaghan, im in monaghan town and the vhf relay at aghabog is next to useless, i have line of sight from my house to it and i always got ghosting/co-channel even my neighbours do and even on an indoor antenna. im not sure what causes it but most of us have opted for rte via clermont, i get a grand analogue picture but digital is very hard for me to get, but neighbour across road about 80ft away gets perfect dtt

John mac

if you have good analogue you should have perfect digital.

Tom Slick

deaglan169 wrote: »

...the vhf relay at aghabog is next to useless, i have line of sight from my house to it and i always got ghosting/co-channel even my neighbours do and even on an indoor antenna. im not sure what causes it but most of us have opted for rte via clermont, i get a grand analogue picture but digital is very hard for me to get, but neighbour across road about 80ft away gets perfect dtt

VHF relay is actually closer to Corcaghan (highest ground to south of town). NGR is; H 634 267. RTE call it Lugad Hill.

Are you thinking of NI DTT (Freeview)?

What about TV3 from Clermont (C66)?

When I said "co-channel" I meant, I think "adjacent channel" i.e. channel E (Kippure RTE1) interfering with "my" RTE2 (channel F).

but......my understanding here is limited.

Mike 1972

Ghosting is almost always going to be more of a problem on indoor aerials regardless of how near one is to the TX

It could be that the ghosting is occurring on the input signal to the relay (affecting everyone who uses it) although its not very likely.

deaglan169 wrote: »

the vhf relay at aghabog is next to useless,...... most of us have opted for rte via clermont,

TBH Where possible its usually better to source yout TV from a main TX rather from a relay. Quality is better (although if the relay is well set up/maintained the difference should be small) and if a major transmitter breaks down RTE are going to be in more of a hurry to fix it.

Oh and most relays dont have TV3 (although some would say its not much of a loss)

Antenna

Tom Slick wrote: »

(dark horizontal/diagonal lines)

Its likely something in your own house causing interference - plug out from the mains or completely switch off (don't just put in standby) everything else electronic in your house one by one - satellite receivers, DVD, down to clock radios and see if there is any difference to the reception.

Does the interference vary if you move about the aerial cables behind the TV?

Tom Slick wrote: »

When I said "co-channel" I meant, I think "adjacent channel" i.e. channel E (Kippure RTE1) interfering with "my" RTE2 (channel F).

Adajacent Channel interference is only going to be a problem if the adjacent channel signal is stronger (not the same strength or weaker).

Tom Slick

Have tried all that.
Must be something external. I may need better cables.
Thanks anyway.

lucernarian

I've heard of TVs causing interference to some parts of the spectrum, particularly VHF. In the case I heard, it was a flatscreen. The problem wasn't noticed for a long time as the TV being switched on to check signal would show interference on Channel E in the first place. If you move your aerial away from the house, say hold it in the garden and check that way, you could more conclusively rule out interference from the house.

Trying at ground level may sound self-defeating, but VHF aerials aren't so affected by height like UHF ones are.