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Strange Signal Problem
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Well so far I have changed the cable to super high quality stuff, have put up a high gain ariel and removed my b & q's crappy amp and replaced it with a 24db gain adjustable masthead amp. It kind of fixes the problem but also creates its own.
The problem I was having was that discovery used to break up now and again and sometimes the screen would just go black for about 5 secs with no sound then come back.
I fixed this by putting the masthead amp on but the problem is when the amp is cranked up it also amplifies the signal from the other mast in my area so that bbc 1,2,3,4 and itv2 are all cancelled out by signals being picked up from both masts.
When I turn the gain down the bbc channels come back and work as normal but the random break ups on discovery also come back.
The guy at the local tv shop thinks that the signal from discovery is coming off the bottom of the mast and so is weaker and loosing strength compred to bbc ect off the top ?.
Is there anyway round this problem, it seems to be a bit of one or another, is a pain, is there anyway I can shield the back of the antenna array so to block the pickup from the other mast ? so that I can crank up the gain so to bring up the signal from discovery and block the signal coming off the back of my ariel ?.
Cheers
Iain
The problem I was having was that discovery used to break up now and again and sometimes the screen would just go black for about 5 secs with no sound then come back.
I fixed this by putting the masthead amp on but the problem is when the amp is cranked up it also amplifies the signal from the other mast in my area so that bbc 1,2,3,4 and itv2 are all cancelled out by signals being picked up from both masts.
When I turn the gain down the bbc channels come back and work as normal but the random break ups on discovery also come back.
The guy at the local tv shop thinks that the signal from discovery is coming off the bottom of the mast and so is weaker and loosing strength compred to bbc ect off the top ?.
Is there anyway round this problem, it seems to be a bit of one or another, is a pain, is there anyway I can shield the back of the antenna array so to block the pickup from the other mast ? so that I can crank up the gain so to bring up the signal from discovery and block the signal coming off the back of my ariel ?.
Cheers
Iain
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Comments
Which transmitter do you receive from, and what's the first part of your post code (e.g. DN16)
NG32
When the amp is turned up full it kills all the bbc channels but discovery is 100% perfect quality, but when you turn it down, discovery starts to play up but bbc comes back to normal
You shouldn't need such a high-gain amplifier at 12 miles from Waltham, unless:
- there is something blocking the signal (trees, buildings, hills)
- there is something very wrong with your cables/connectors/aerial
If it's the former, then try Belmont instead but bear in mind that you need a Wideband aerial.
We have tried using belmont before with the digibox but the signal is really bad and breaks up a lot.
The reason I suspected it was interfering from the other mast is because when you put it onto normal tv with the digi box off and turn the gain up on the amp you can see two channels in one, as it seems to ghost another channel over the top from the other mast.
The wire up should be....
Aerial - signal amp - set top box (freeview) - tv
*Make sure the signal amp is plugged in and switched on. If you wan't to try without the amp, dont just switch it off - it breaks the aerial connection. In that case, you should "bypass" the amp - usually by joining the aerial wires together with one of those little back to back plugs.
**If the signal is really strong where you live, maybe you could remove the signal amp, and plug the aerial direct into the freeview set top box. If you experiment like this, after making any changes, you would need to do a channel scan.
Dave
ARIEL ~ MASTHEAD AMP ~ MASTHEAD PSU ~ SET TOP BOX
Then the scart from there goes to the tv, then the second output from the digi box marked video goes to the video recorder and dvd which are on standby or off anyways unless they are being used.
The thing about taking the amp off and trying it without it is that when you turn the amp down to its lowest point discovery signal is crap but when you crank it up it is perfect, this would point to poor signal though wouldn't it ?.
The only problem being is that this overpowerful signal seems to kill bbc ect, I need a way of like selectively amplifying channels or something, very confusing
Not sure what the area & transmitter locations are like, so its difficult to say for sure. A channel re-scan might help to remove the weak signals and replace them with the same thing from the local mast (with the strong signal).
If it is co-channel signals being picked up, it might be possible to block the unwanted signals with a signal blocker, or maybe even use a "low gain" Grouped aerial to null out the unwanted signals. A "focused" aerial which need good alignment might also help as it would be less prone to side pick up.
Dave
You're problem is cross modulation caused by the amplifier.
Although you are boosting the digital signals, you are also boosting the much stronger analogue signals which is causing the cross modulation and degrading the signal quality of the weaker digital signals.
Looking at the channel list for Waltham, the digital signals are between ch23 - 49 but the analogue channels are between ch54 - 64.
It is possible that if you change your aerial for a Group A one and use the amplifier that it may solve your problems (but it's not guaranteed).
I suspect that the output from the amp is overloading the digital box and your Tv tuner, so you could try a 6db in-line attenuator at the Freeview box end, this will be reducing the signal without the loss in the coax feeder cable.
You can also buy adjustable in-line notch filters which can be tuned to notch out the stronger analogue channels without affecting the digital channels.
No!! You need to keep the amp at the aerial end as you need to boost the signal from the aerial before any losses in the coax cable. You can then try and attenuate the signal with a 6 or 12db in-line attenuator so as not to overload your digi box.
You can get notch filters but they are about £20 each and you would need 4 or 5 (one for each analogue channel) and the insertion loss of 5 filters may cause more problems. > http://www.jwhardy.co.uk/shop/pages/pl_filters.html
I still think your best bet is to install a high gain Group A aerial and a single stage masthead amplifier, this should have a low noise figure and no more than 12db gain. For the best results you need to get as much gain as possible from the aerial, the amplifier should only be used to over come any losses in the coax cable.
If you have installed a wideband aerial, then these tend to have lower gain on the lower channels, in your case this is where you need the most gain and this is why i'm suggesting a high gain Group A aerial.