Mains interference: Digital TV problems

Hi, New to this group.
    We have the now common set-top box for digital terrestrial TV and
radio.
    We get a lot of intereference: Picture break-up and loud clicks in the sound. Sometimes making a programme unwatchable. We have managed to reduce this: The aerial has been upgraded, and there's a filter on the mains socket supplying the AV equipment.
    However, we get serious problems when we have a fan running, the washing machine is on, or we run the hot tap (It's one of those that turns on a heater to heat the water as you use it).
    I'm not sure whether the appliances concerned are generating radio waves, or are spiking the mains supply.
    From the research I've done, the next step to getting a clean signal is upgrading the aerial cable, filtering the appliances in question, or providing a dedicated (shielded) ring main for the AV equipment.
    The first and last options are going to be a bit tricky, since the aerial cable is routed in walls and all sorts, and I'm not convinced that a decicated ring main will be cost-effective.
    Is it possible to put chokes or filters of some sort on the offending appliances? If so, advice on how to do it would be most welcome (240v 50Hz supply).
--
Regards,
Dave
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 10 Jun 2006 13:38:33 GMT, Dave Ryman

My "off air" HDTV reception is fine using a set top antenna. Try one. You mat find that your in wall post wire installation of your antenna feed has some "RF holes" in it. At least big enough to let the noise from an AC appliance affect it.
Rabbit ears work great on my HDTV off air tuner.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Gave us:

I don't think we'd get enough gain from such an aerial - our geography is such that an aerial on the ground floor probably won't be high enough.
--
Regards,
Dave
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 10 Jun 2006 19:29:02 GMT, Dave Ryman

OK, then is the coaxial cable run from you antenna to your tuner a "home run"? That is a single cable run, with no breaks (unions) in it. You have at least ONE as you are getting it from a wall outlet. If you have enough slack in the wall, remove the wall plate, and bring the cable out "flying lead" style.
Each break costs a couple db.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
(snip)

That's interesting - mind you, I always thought that standard coax connectors were a bit hopeless. Any thoughts on BNC connectors?
Looks like I'm going to try replacing the whole length of cable - wish me luck!
Thanks for all the advice.
--
Regards,
Dave
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

its also bullshit. conector loss might be about .1 dB.... granted having as few splices as possible is a good thing.
mind you, I always thought that standard coax

check the easy stuff first.... look for an open balun on the antenna.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
(snip)

Just looked "balun" up. Our aerial is a new one. Am I right in assuming that, in our case, the balun is the small plastic box on it within which the coax attaches? If so, ours is fine. If I'm talking B*llocks, then someone please let me know!
--
Regards,
Dave
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave Ryman wrote:

restating the problem:
" We have the now common set-top box for digital terrestrial TV and radio.
We get a lot of intereference: Picture break-up and loud clicks in the sound. Sometimes making a programme unwatchable. We have managed to reduce this: The aerial has been upgraded, and there's a filter on the mains socket supplying the AV equipment.
However, we get serious problems when we have a fan running, the washing machine is on, or we run the hot tap (It's one of those that turns on a heater to heat the water as you use it)."
to me this sounds like some kind of ground loop issue.
just try this: get 2 low cost baluns. they have an F connector at one end and 2 spade terminals at the other. solder or bolt the spade lugs to the matching lug on the other balun. this gives you a 75 ohm F connector at each end. add a short male - male cable and insert at the receiver.
if this does not help then you can proceed to more drastic and expensive measures.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That sounds like it's worth a try. I've being researching baluns, and my head now hurts.
Thanks.
--
Regards,
Dave
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave Ryman wrote:

i had assumed that you had a solid signal except for the interfearance problem.
another possibility is to add a inline amplifier at the antenna. this boosts the signal a bit. it is then attenuated by the length of coax. a inline section is added at the receiver end to power the amplifier.
it looks something like this http://www.audio-discounters.com/bia-20.html
check to see if there are any splitters in line and remove if possable.
i understand you have to license TVs in the UK. would that apply to the digital box too?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Got an in-line amplifer already, thanks.

Need an inline spliiter, I'm afraid - these digital boxes only give one output, so you need more than one digibox if you want to record a program whilst watching another.

Yep, any TV that's capable of receiving and displaying a TV picture.
--
Regards,
Dave
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
(snip)

I've just tried this, and it works an absolute treat!! The Lion's share of the interference has gone. Such a simple thing - I'm not even going to try to pretend to understand the physics, I'll just apply Arthur C. Clarke's definition of "Magic"!
Thanks very very much.
--
Regards,
Dave
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave Ryman wrote:

sometimes you get lucky with an easy fix. of course the first time i ran into a goofy situation where an audio production studio just had to have a cable installed and it created a buzz in the audio i was beating my head against the wall (figurititivly) until i hit upon this workaround.
some additional info can be seen here http://www.epanorama.net/circuits/antenna_isolator.html
next step is to eyeball the coax cable and see if there is a grounded (earthed i guess you would say) feed through 'block' somewhere outside. if not add one. something like this http://www.dxengineering.com/Parts.asp?ID $5&PLID&SecIDH&DeptID&PartNo=PPC-IS-75FB%2F18
the idea is to try and keep lightning outside your house and anything you touch (like the connector) at ground potential.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 21 Jun 2006 02:03:25 -0400, "TimPerry"

Your goddamned link should be E-SPAMorama!
It spammed me with pop ups!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

it was not intentional Roy, i use a proxy server to block pop-ups and banners (proxomitron) so i had no idea it would do that.
the site does have a visual drawing of the balun arangements i was discussing.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 21 Jun 2006 20:08:49 -0400, "TimPerry"

I know it's hard to tell, but I was just being facetious... :-]
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave,
I assume you are in the UK.
It's possible that the signal strength of the digital signal is marginal - which would cause the symptoms which you describe.
The digital transmitters run at much lower powers (~10kW ERP) as opposed to the analogue transmitters (can be up to 1MW ERP) and although you may be getting a satisfactory analogue signal the digital signal may well be near to the receiver's threshold.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It all comes down to bit-error-rate with digital. Once it gets above ten percent, anomalies start to appear. Picture gets artifacts, sound drops out... entire image goes blank, no sound.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yep, in the UK. I suspected the power used to transmit digital was poor, but didn't realise it was just 10% of the analogue signal - no wonder there's problems! And they want to turn the analogue off in a few years: They must have shares in the companies that make aerials, coax and connectors.
--
Regards,
Dave
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I live in a margin area and the digital signal does tend to drop in and out exactly as you described in your OP. It's also weather dependent - the hotter summer months are worse than the cooler winter/spring/autumn.
I would firstly check all your connectors and ensure the centre of the coax is soldered to the centre pin of the plug (for our US readers we don't use F type connectors for Terrestrial TV, they're only found on satellite equipment).
Then if the connections are sound, try to get the aerial checked by someone who is competent - look for someone who is a member of the CAI Confederation of Aerial Installers.
Like you I'm also wondering about the analogue turn-off. Hopefully they may be able to up the power of the digital transmitters once the analogue TXs are turned off and the spectrum is freed up.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.