SD STB problem with 2 local Translators.

[gordon_s1942]

The town of Lithgow NSW, has 2 translators serving the valley due to its shape.
Each rebroadcasts the programs originating from Orange and carries ABC/SBS/WIN/Prime and SC.
The oldest translator still carries Ch6 VHF Vertical along with the UHF analog and Digital Horizontaly polarised.
The newest is UHF only, both analog and digital, horizontal polarised and is 'shaped' to cover the area the other one doesnt due to the valley shape.
Obviously there are place both can be 'seen' for reception and herein lies a problem with a STB.
The 'New' one I should point out had been there now for at least 20 year.But it is 'NEW' because 2 years ago during a bad Winter wind storm, the mast collapsed and bent in half.
Oddly enough for some, it hardly affected their reception on analog although the digital on some channels only was badly affected.
The Problem.
My friend lives near the 'New' translator and antenna facing UP as the 'New' translator is located up on the escarpment at least 100 metres higher than the houses.
He has experienced an almost total freeze on the WIN channel.
With his antenna pointed DIRECTLY at the 'New' translator, the 'OLD' translator is roughly 45 degrees to the Left in front of the antenna.
The'OLD' translator I guess would be about 3 times further away than the 'NEW' one
He rescanned for 'GO!!' and it too of course isnt viewable.
All the others are crystal clear.
I rescanned it yesterday and watched as the STB found 3 seperate services.
3??? where is the third comming from?? At the moment that is to sorted out later but his STB when I reran the channel listing, it only showed one set of services.
For some reason, the WIN service it found is on the 'OLD' translator and is poor.
There was no sign in the listing of WIN from the 'New' translator.
I didnt have time yesterday to note all the frequencies shown as it scanned but that will have to be done.
I took his STB off line and used an old SD Omni, it searched and it happily locked onto the full service from the 'New' translator, plus it showed the channels from the 'Old' translator. WIN was clear on the 'New' line up but poor on the 'Old' as expected.
I dont know how many places have totaly seperate translators under a KM apart covering an area like the Lithgow Valley.


BTW the friends SD STB that we are having fun with is a Coles MTV brand (Sorry Col).
As usual, get the grey cells circling and lets see what happens.

PS, there is a 3rd translator at Hassans Walls but it is analog only,very low power and doesnt carry SBS that I know off and its directed well away from the area I am talking about.
***********
I forgot to describe his setup.
One 15 element or so Yagi, chimney mounted, Hor, about 6m of coax to a splitter, one leg to a MyStar box, the other to the digital STB.
Using his setup, I had no trouble tuning and viewing the 'New' translator with my Omni SD box.

[vmark]

The town of Lithgow NSW, has 2 translators serving the valley due to its shape. Obviously there are place both can be 'seen' for reception and herein lies a problem with a STB.

Ok, both should have totally different channels on them, regardless of Analogue or Digital transmissions and possibly different polarisations too.

I rescanned it yesterday and watched as the STB found 3 seperate services. For some reason, the WIN service it found is on the 'OLD' translator and is poor.

If this translator is now 45 degrees away from the "other" then it may well be now living in a Null point of your antenna, hence the low signal level. You'd have to see a plot diagram for the antenna you've got to see the null points.
Check the ACMA web site for the Channels Freqs etc for your area.
Good luck

[mtv]

Gordon,

Firstly, the MTV brand STB has a history of reception issues, which certainly won't help in this case.

I suspect the main issue is that the area is serviced by translators on a SFN (Single Frequency Network) which means they share frequencies for the same channels from more than one transmission site.

Portland/Wallerawang and Lithgow East use identical digital frequencies and polarisation. All digital channels are in the upper part of UHF Band 5.

Portland/Wallerawang TX are mostly 1kW and Lithgow East, 50W, so there is a big power difference.

With SFN's, if signals are being picked up by the receiving antenna from more than one transmission site, they can (and often do) interfere with each other.

This is where a spectrum analyser comes into it's own, being able to display all SFN signals simultaneously, enabling the antenna installer to position the antenna in a spot which optimises the signal from the best transmission site and minimises all other signals.

The receiver will then be able to decode the digital data stream more reliably.

The third signal area is likely to be from Lithgow, from which all digital channels are in UHF Band 4, except WIN, which is in Band 5 on channel 44.

In SFN areas, highly-directional, narrow beamwidth antennas generally provide the best results.

Natural bulding features, such as metal roofs or walls, can also act to reduduce unwanted signals from other transmission sites.

Once again, without the assistance of accurate signal metering/measuring equipment, it's all but impossible to find the best-possible antenna location and alignment.

[gordon_s1942]

MTV is correct on the shared frequencies between Portland/Wallerawang and Lithgow East but there is no way he should be able to receive the Portland/Wallerawang translator due the reason it is over 15 kms away, Vertical to Lithgow East Horizontal and his house is down behind the 200 metre high escarpment of the mountain ridge that is the western wall of the Lithgow Valley.
The other translator is on Reservour Hill and it has it own channels which the Magnavoz HD STB prefers to find instead of the Lithgow East one.
Vmark, Both the translators serving the Lithgow Valley are Horizontal for UHF and use different frequencies for each channel, that is not the problem in this case.

It seems that the Magnavox just doesnt like his situation as an old Omni SD STB is working ok there at the present.
He is thinking off replacing his old antenna and along with new cable, relocating a new antenna to a different side of his house.

[mtv]

Although there may not be LOS, there may be sufficient reflected signals from the higher-powered Portland/Wallerawang TX to be causing an SFN conflict issue. I've seen this scenario several times.

That's not to say this is the case in this instance, but there's a possibility.

This is where accurate signal measurements come in... separating fact from theory/guessing.