[mythtv-users] DVB-T Hell in Sydney

Doug Scoular (dscoular) dscoular at cisco.com
Sun Jun 26 08:22:59 UTC 2016


Hi Mark/John,

On Wed, 22 Jun 2016 Mark Perkins wrote:
>I'm not 100% sure, but I don't think **from a mythtv perspective** that
>polarisation would be relevant to tuning an individual dvb-t channel
>(clearly it is important for your antenna etc). The details for the
>dtv_multiplex table suggest that the polarity field has no default value
>but
>the notes imply that it's usage is for dvb-s (satellite). My guess is that
>the channel scan process is just chucking a 'v' value in there (rightly or
>wrongly) for dvb-t. I have just checked my database and I have a
>horizontally polarised antenna and transmitter but I also have the 'v'
>value
>in my polarity field. I would ignore the polarity field for now.
>
>My very very rough calcs based on a very very rough memory of how radio
>attenuation works says that over linear unobstructed terrain the Newcastle
>transmitter would be approximately 10times more powerful at your location
>compared to the Bouddi transmitter. Once you include that your antenna is
>polarised to match the Newcastle transmitter and that the frequencies in
>your table match the details published online for the Newcastle
>transmitter
>I would say with extremely high confidence that you are receiving the
>Newcastle transmitter channels. Whether you would be better off changing
>your antenna polarisation to match Bouddi would be subject to an analysis
>of
>the obstructions over the two paths (or some experimentation with
>something
>that can report signal strength and bit errors, maybe tzap or dvbscan or
>equivalent) but my thoughts are that you would be better off sticking with
>Newcastle for now.
>

And on Wed, 22 Jun 2016 John Pilkington wrote:
>If your antenna has horizontal elements it's likely it was set up for
>Newcastle.  The polarisation entry in the DB is a default value, and
>irrelevant.  The frequencies in your DB identify the mux and the
>transmitter.  I would try using the Transport Editor to delete all the
>Bouddi muxes.  If results are bad, rotate (and re-point?) the antenna
>and delete the Newcastle muxes instead.


	Well I spent a large part of the weekend playing around with
	the antenna. When I set it to vertical to match Bouddi, created
	my own custom Bouddi frequency initial tuning file and attempted
	a scan, it would only pick up SBS and Nine. The interesting thing
	was that some of the channels have a prefix of "Sydney". Nine's
	channels were quite strong but the SBS channels were marginal.
	When I placed the antenna back to horizontal to match Newcastle
	I got all my channels back but this time I noticed that many of
	them had "Newcastle" as a prefix in their name. This seems to
	confirm the theory that I'm getting signals from Bouddi and
	Newcastle

	Here are some of the Newcastle and Sydney specifc names I've
	been getting:

7mate Newcastle
7TWO Newcastle
PRIME7 Newcastle
NBN Newcastle
9HD Newcastle
9GEM Newcastle
9GO! Newcastle
9Life Newcastle
SC10 Newcastle
ONE Newcastle


SBS Sydney
Channel 9 Sydney
9HD Sydney

	So it looks like I'm getting a vertical signal from Bouddi which
	is relatively weak compared to the horizontal signal I get from
	Newcastle. I suppose having Scotland Island and West Head in the
	way doesn't exactly help things.

	I retuned MythTV and was rewarded with all my Newcastle channels
	being pretty solid. So I guess I'll just settle for the fact that
	I'm not using the closest transmitter but the one giving me the
	best signal.

	Thanks so much to everyone who took the time to read through my
	gargantuan thread and helped me to gain a little more insight
	into the world of DVB-T tuning.

	I can't begin to express how happy Myth TV has made me over the
	years.

	Cheers,

	Doug
	"The big print giveth and the small print taketh away".



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