TV on different aerial causing interference?

"Ian Jackson" wrote in message
...
In message , Woody
writes
"Al" wrote in message
. 1.4...
Strange one this ...

Parents got a new TV for their kitchen recently (Samsung LE19R8) and
sure
enough their indoor aerial wasn't good enough as expected.

So, they had another aerial installed and a seperate downlead to the
kitchen. The aerials are both on the same chimney mast and the
downleads
run along side each other until they reach a lower level and go
their
seperate ways. (No, I don't know why they didn't get a booster and a
splitter).

2 TVs in the front room, one old analogue and an IDTV fed from one
aerial
with a passive splitter (yes, I know). There's a VCR in there
somewhere
also. Kitchen TV on it's own aerial.

Everything works fine ... Until the kitchen TV is put on ITV on
digital,
and then Channel 4 in the front room is unwatchable on analogue -
Snowy
vertical rolling. Fine on digital on the IDTV. Change channel on the
kitchen TV or go to ITV via analogue and everything is fine.

If I swap the kitchen TV and the analogue TV over there is no
problem.
It
sort of implies that there's something weird happening when the 2
digital
TVs are on different aerials.

I wanted to remove the VCR and the splitter and try some more
combinations
but the parents are paranoid that it won't work again (nice to be
trusted!).

I can't believe that the kitchen TV is putting interference up the
aerial
lead and that it's cross coupling with the other aerial. The coax
looks to
be good quality foil shielded and both aerials seem to be giving
good
signal strength.

I'm baffled

Al.



Likely that the local oscillator (or possibly the computer clock) is
getting back up the aerial and coupling across to the analogue aerial
or
downlead.

If you swap the TVs you said yourself that there is a VCR in there and
if the TV is the last item in the chain then there is no path back
through the VCR to the aerial - many VCR local outputs are amplified.

As others have said relocate one of the aerials, or if you have enough
signal fit an attenuator in the DTTV cable at the TV end. You will
then
maximise the interferring losses and possibly reduce it enough to
remove
the Ch4 problem.

For analogue channels, the 'N+5' and 'N=5' allocations were strictly
been abandoned? If so, I can see some muxes getting clobbered by an
analogue TV tuned to a channel five channels down.

But maybe they have still avoided this relationship? For example, I
see that, with the Crystal Palace allocation, no digital mux is N+5
wrt an analogue channel. However, there are three allocations where
there is something N+5 wrt a digital mux (25 on 30 analogue, 28 on 30
analogue, and 29 wrt 34 digital).

But do the digital STBs and TVs have the same local oscillator and IF
as analogue TVs - or do they use something different? If they are the
same, do the digital tuners simply have much less radiation of the
local oscillator?
--
Ian


Emley (which I use) is analogue 37, 41, 44, 47, 51 and digital is 40,
43, 46, 49, 50, 52.

My simple maths suggests that the N+5/N=5 rule is truly no more.


--
Woody

harrogate three at ntlworld dot com

Cross coupling does occur of course, I can hear it on two fm radios with
two aerial in different directions if I pull the plug on one, it affects
levels of noise on the other.
Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Al" wrote in message
. 4...
Strange one this ...

Parents got a new TV for their kitchen recently (Samsung LE19R8) and sure
enough their indoor aerial wasn't good enough as expected.

So, they had another aerial installed and a seperate downlead to the
kitchen. The aerials are both on the same chimney mast and the downleads
run along side each other until they reach a lower level and go their
seperate ways. (No, I don't know why they didn't get a booster and a
splitter).

2 TVs in the front room, one old analogue and an IDTV fed from one aerial
with a passive splitter (yes, I know). There's a VCR in there somewhere
also. Kitchen TV on it's own aerial.

Everything works fine ... Until the kitchen TV is put on ITV on digital,
and then Channel 4 in the front room is unwatchable on analogue - Snowy
vertical rolling. Fine on digital on the IDTV. Change channel on the
kitchen TV or go to ITV via analogue and everything is fine.

If I swap the kitchen TV and the analogue TV over there is no problem. It
sort of implies that there's something weird happening when the 2 digital
TVs are on different aerials.

I wanted to remove the VCR and the splitter and try some more combinations
but the parents are paranoid that it won't work again (nice to be
trusted!).

I can't believe that the kitchen TV is putting interference up the aerial
lead and that it's cross coupling with the other aerial. The coax looks to
be good quality foil shielded and both aerials seem to be giving good
signal strength.

I'm baffled

Al.

In message , Woody
writes
"Ian Jackson" wrote in message
...
In message , Woody
writes
"Al" wrote in message
.1.4...
Strange one this ...

Parents got a new TV for their kitchen recently (Samsung LE19R8) and
sure
enough their indoor aerial wasn't good enough as expected.

So, they had another aerial installed and a seperate downlead to the
kitchen. The aerials are both on the same chimney mast and the
downleads
run along side each other until they reach a lower level and go
their
seperate ways. (No, I don't know why they didn't get a booster and a
splitter).

2 TVs in the front room, one old analogue and an IDTV fed from one
aerial
with a passive splitter (yes, I know). There's a VCR in there
somewhere
also. Kitchen TV on it's own aerial.

Everything works fine ... Until the kitchen TV is put on ITV on
digital,
and then Channel 4 in the front room is unwatchable on analogue -
Snowy
vertical rolling. Fine on digital on the IDTV. Change channel on the
kitchen TV or go to ITV via analogue and everything is fine.

If I swap the kitchen TV and the analogue TV over there is no
problem.
It
sort of implies that there's something weird happening when the 2
digital
TVs are on different aerials.

I wanted to remove the VCR and the splitter and try some more
combinations
but the parents are paranoid that it won't work again (nice to be
trusted!).

I can't believe that the kitchen TV is putting interference up the
aerial
lead and that it's cross coupling with the other aerial. The coax
looks to
be good quality foil shielded and both aerials seem to be giving
good
signal strength.

I'm baffled

Al.



Likely that the local oscillator (or possibly the computer clock) is
getting back up the aerial and coupling across to the analogue aerial
or
downlead.

If you swap the TVs you said yourself that there is a VCR in there and
if the TV is the last item in the chain then there is no path back
through the VCR to the aerial - many VCR local outputs are amplified.

As others have said relocate one of the aerials, or if you have enough
signal fit an attenuator in the DTTV cable at the TV end. You will
then
maximise the interferring losses and possibly reduce it enough to
remove
the Ch4 problem.

For analogue channels, the 'N+5' and 'N=5' allocations were strictly
been abandoned? If so, I can see some muxes getting clobbered by an
analogue TV tuned to a channel five channels down.

But maybe they have still avoided this relationship? For example, I
see that, with the Crystal Palace allocation, no digital mux is N+5
wrt an analogue channel. However, there are three allocations where
there is something N+5 wrt a digital mux (25 on 30 analogue, 28 on 30
analogue, and 29 wrt 34 digital).

But do the digital STBs and TVs have the same local oscillator and IF
as analogue TVs - or do they use something different? If they are the
same, do the digital tuners simply have much less radiation of the
local oscillator?

Once again, correcting my mistake... Should be 28 on 33 analogue.

Emley (which I use) is analogue 37, 41, 44, 47, 51 and digital is 40,
43, 46, 49, 50, 52.

My simple maths suggests that the N+5/N=5 rule is truly no more.

You're dead right. A41 hits D46, and A47 hits D52. I'm surprised that
this does not cause the occasional problem. D46 also hits A51 but,
assuming that digital tuners are engineered to a much higher standard,
and don't radiate much local oscillator, that might be OK. Maybe the
whole N+5/N-5 was a complete myth!
--
Ian

charles wrote:
In article ,
Al wrote:
Strange one this ...

[Snip]

I can't believe that the kitchen TV is putting interference up the aerial
lead and that it's cross coupling with the other aerial. The coax looks
to be good quality foil shielded and both aerials seem to be giving good
signal strength.

not knowing where you live, and therefore which transmitter you receive,
make a proper diagnosis difficult. I would think that your kitchen tv is
indeed sending a signal back up the aerial lead and that is getting across
into the other aerial. This does happen, or certainly used to in the
analogue days. The solution is to move the two aerials further apart.


What would be a recommended minimum separation?

When some houses near my home were being re-roofed,
the contractors re-fitted aerials up to 6 to a mast,
barely a foot apart. They were all pointing at an
analogue relay within line of sight (and with no
Five), so there might have been less of a problem.
The greater problem was the masts all bent over in the
first gale, though the signal was probably still OK.

A similar query was posed some years ago and the answer then was that
when too many TV aerials are placed closed to each other they
interfere causing them, and I quote, "to detune each other".

Move the aerials apart, or remove one aerial and have both TVs fed off
the same aerial.

John

Ian Jackson wrote:


Emley (which I use) is analogue 37, 41, 44, 47, 51 and digital is 40,
43, 46, 49, 50, 52.

My simple maths suggests that the N+5/N=5 rule is truly no more.

You're dead right. A41 hits D46, and A47 hits D52. I'm surprised that
this does not cause the occasional problem. D46 also hits A51 but,
assuming that digital tuners are engineered to a much higher standard,
and don't radiate much local oscillator, that might be OK. Maybe the
whole N+5/N-5 was a complete myth!

No it's not a myth, but there are two things to remember. Firstly the
image rejection performance of modern tuners is very good, secondly the
whole rationale behind fitting DTT into the UHF band alongside the
analogue channels was to make use of what were previously 'Taboo'
channels. i.e. N+/-9, N=/-5, and indeed N+/-1.

"Woody" wrote in message
...
"Ian Jackson" wrote in message
Emley (which I use) is analogue 37, 41, 44, 47, 51 and digital is 40, 43,
46, 49, 50, 52.

My simple maths suggests that the N+5/N=5 rule is truly no more.

The n+9 rule hasn't been obeyed for ten years. Bilsdale analogue includes 26
and 35.

Bill

"Ian Jackson" wrote in message
...
You're dead right. A41 hits D46, and A47 hits D52. I'm surprised that this
does not cause the occasional problem. D46 also hits A51 but, assuming
that digital tuners are engineered to a much higher standard, and don't
radiate much local oscillator, that might be OK. Maybe the whole N+5/N-5
was a complete myth!

Some of these very cheap flatscreen supermarket sets have brought it back! I
always get the impression that the manufacturers know how to make a screen,
but have no idea about adding the RF bits! T'other day the customer had a
19" set which had cost £89.99. The performance of the analogue tuner was
truly dreadful. Incidentally, the customer thought (asumed?) that the set
was 'all ready for digital' but it didn't have a digital tuner. I added a
DTT set top box (because the picture on analogue was so bad) and bugger me
the picture via the (composite) scart had a pattern of fine lines (looked
like internally generated interference) and the RGB scart was very dull and
couldn't be adjusted.

Bill

"Jim" wrote in message
net...
charles wrote:
When some houses near my home were being re-roofed, the contractors
re-fitted aerials up to 6 to a mast, barely a foot apart.

Like this?

http://www.wrightsaerials.tv/roguesg.../061.html#img1

Bill

wrote in message
...
A similar query was posed some years ago and the answer then was that
when too many TV aerials are placed closed to each other they
interfere causing them, and I quote, "to detune each other".

Move the aerials apart, or remove one aerial and have both TVs fed off
the same aerial.

It won't help if the problem is IF going up the cable from one set.

Bill