[mythtv-users] three questions with DVB-T

Matt Harrison iwasinnamuknow at genestate.com
Tue Apr 5 10:46:01 UTC 2011

On 05/04/2011 08:28, Martin Moores wrote:
> On 5 April 2011 02:31, Robert Humphrey<mythtv at robhumphrey.me.uk>  wrote:
>> I'm using two dual DVB-T tuners, both connected to the same aerial
>> Can you give a bit more detail about what these tuners actually are?  How
>> are they connected to the aerial and does each device have one or two aerial
>> inputs?

Certainly, should have done this before. They are two different brands 
of USB tuner but both pretty much identical, based on the Aftech AF9015 
chipset. One is an MSI Digivox DUO and I'm afraid I can't remember the 
other right now.

There is one rooftop aerial which comes in to a signal amplifier and is 
then split into two, one for each tuner.

>> The reason I ask is that I have a Nova-T Dual USB tuner, and from using
>> tzap (see http://www.mythtv.org/wiki/Tzap ) I can see that enabling the
>> second tuner has a negative impact on the signal level and quality to the
>> first tuner.  If the signal level/signal to noise ratio is marginal then
>> changes in atmospheric conditions could be providing the 'pretty random'
>> effect you're seeing with it sometimes not getting lock.

I had heard about the second tuner sometimes affecting the first, but 
personally I haven't seen any change in quality etc when there is a 
recording happening for example.

>> I have noticed that the signal level and quality appears to need to be much
>> better to get initial lock than it does either once lock has been
>> established or to scan for the channels.

Yes I had suspected that.

>> If your tuners are USB, one thing worth trying is connecting them via USB
>> cables and placing them a little way away from the PC.  Try to ensure the
>> aerial cable does not go near the PC/power supplies either.  I found that
>> doing this reduced the noise just enough to give me much more reliable lock.

They are currently on USB extension cables but I might be able to route 
the aerial better away from the machine. I'll give that a go when I get 
a chance.

>> Hope this helps
>> Rob

Thanks Rob

> I have a Nova-T, it did as you descibe for years and I just put up with it,
> had to cold boot the machine to fix it, even that sometimes didn't work.
> After seeing a message on this list, I turned off active EIT scanning for
> the second tuner.  After this, have never had a failed recording.  Some info
> here:
> http://www.youplala.net/linux/home-theater-pc#toc-not-losing-one-of-the-nova-t-500s-tuners

Sounds somewhat familiar, I'll have a read of that.


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