[mythtv-users] Digital Signal seems to weaken sometimes

Roger Heflin rogerheflin at gmail.com
Sat Jun 14 13:21:06 UTC 2008


David Whyte wrote:
> On Thu, Jun 12, 2008 at 9:09 PM, Lindsay Mathieson
> <lindsay.mathieson at optusnet.com.au> wrote:
>> Could there be a electrical device
>> nearby starting up - AirCon/Heating, Microwave etc?
>>
> 
> 
> Narrowed the problem down to a single power adapter.  It seems that
> whenever the AOpen miniPC frontend in one of the rooms was turned on,
> it would cause the TV signal to weaken on that TV and around the
> house, but particularly on the digital tuner cards in my backend.
> 
> All the cables on the TV and frontend had been zippy tied together so
> I disconnected them all and that has certainly stopped the
> interference from being so great that the tuner cards couldn't record.
>  I have noticed though that whenever the transformer for the miniPC is
> plugged in and turned on it causes some noticeable interference on
> that one TV.  The level of interference changes as I move the power
> cable for the adapter around the power and ariel cable for the TV.  I
> have an identical adapter for another miniPC and that has the same
> effect, but on that one TV only.  Similar adapters for different
> laptops do not have the same effect on that TV.
> 
> The miniPCs were purchased from the US, but they are rated for
> Australian use.  The are marked as 'Replacement Adapters' and don't
> have any other branding on them.
> 
> Does anyone have any ideas why these particular adapters are affecting
> just this one TV?
> 
> Any help is greatly appreciated. Kind Regards,
> Whytey

Assuming that the antenna feed is a coaxial connection you should not be able to 
get significant interference based on were the cable is run.   If you are using 
a non-coaxial connection you need to be very careful with routing of the cable.

Given what your symptoms and assuming that you are using a coaxial connection, I 
would check to make sure the ground is connected on everything.   Check the TV 
antenna cable, check power to make sure it has a good proper ground.    I have 
seen antenna cables that don't have the ground connected at all and this does 
funny things to the signal.   I don't know what the power plugs look in AUS, but 
in the US there is a ground connection wire, and if you take a voltmeter and 
measure the resistant from power ground to antenna ground it should be pretty 
low (way less than 1ohm), if it is not either the power or the antenna has a bad 
ground connection and you will get all sorts of funny things happening.

                                Roger


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