[mythtv-users] No reception or EIT for Channel 5 in Essex

Allen Edwards allen.p.edwards at gmail.com
Tue Sep 16 19:32:25 UTC 2008


On Tue, Sep 16, 2008 at 10:57 AM, peter nikolic
<p.nikolic1 at btinternet.com> wrote:
> On Tuesday 16 September 2008, Paul Clark wrote:
>> Just to finish this dicussion for anyone who was interested - or might
>> stumble across this in the future.
>>
>> When I plugged the aerial directly into the TV it all worked fine,
>> likewise when I plugged the aerial straight into one of the tuner
>> cards and not through the splitter.  So I guessed that the splitter
>> combined with my poor reception was the most likely problem.
>>
>> After googling around I found a lot of people recommending the Philex
>> SLx2 2 way TV Aerial Signal Booster.  I bought one of these from eBay
>> and replaced the cheap Y splitter with it.  My problem is fixed and
>> generally the reception on all channels has been improved.
>>
>> Thanks for everyone's help and suggestions along the way.
>>
>> Cheers, Paul
>>
>> 2008/8/31 Mark Fraser <mythtv at mfraz.orangehome.co.uk>:
>>
>
> Hi .
> Having read  this sort of thing so many times i think a little short sharp
> education is called for re joing coax cables together .
>
> Coax Cables as used for TV's have an Impeadance of 75 Ohms  this is the
> impeadance of the Aerial (or roughly so)  Now if you have a downlead from
> your chosen Antenna this is 75 Ohms if you now put one of these cheap and
> disgustingly NASTY splitters in and feed 2 TV's from this you have just
> doubled the load on the very small signal that is available to start with
> for the simple reason 75 ohms in parralle with 75 Ohms = 37.5 Ohms a big no
> no this is like trying to power one of the headlamp bulbs from your car of a
> PP3 9 volt battery it dont work .
>
> This is why you must always use and ACTIVE splitter ie one that has a
> distribution amp and im peadance matching for each output.
>
> Also  this applies to the UK as far as i know the connectors used on TV coax
> are CRAP the method of just strip and push them together is no good  the
> center pins need soldering and the braid needs a good connection ,   COax
> also does not like water at all full stop . if you are serious about your
> recieved signals then the moment any part of the braid or center conductor
> looses it's sheen it's scarp time so pay a lot of attention to the connection
> and seal topside .
>
> Hope this helps a few avoid one of the common problems that arise from poorly
> installed coax ect ..
>
>
> Cheers   Pete .
> G6NJR
>

A few things are not quite right in this post so I thought I might
clarify them.  First, the antenna is almost certainly 300 ohms, which
is why people used to use 300 ohm twin lead to connect to them.
Mostly today people use little 4:1 transformers to transform the twin
lead connection at 300 ohms to 75 ohms, the impedance of the coax.

The most common splitters over hear are actually hybrid splitters and
do not mismatch the signal as was described above.  So, if  you put a
75 ohm load on each of the two outputs, the input will still look like
75 ohms.  Each output gets 1/2 the power of the input plus a little
bit is lost in the coupler (splitter).

The best reception is usually gotten when you put a preamp at the
antenna before the coax and the splitters.  That is because you lose
considerable signal in the coax itself and of course the loss in the
splitters as described above.  I use RG-6U coax which is a lot better
than RG-59.  I also use waterproof connectors called snap-n-seal.
They require a special tool to attach them but there are some cheap
manual tools available.

Hope this helps,

Allen
AA6EX :-)


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