DTT - Interference from MMDS signal

glog

I have a bit of a weird problem.
I picked up a few of the Sagem IDT81 STB's in the UK over the weekend.
Tried to install it/try it out in my friends house.Located near Cork (Carrigaline), he has the following on his aerial pole:
- MMDS Yagi Aerial with integrated downconverter
(Output frequency: 662MHz- 848MHz)
- Colourking aerial (Vert) to receive Southcost deflector channels
- Colourking aerial (Hor) to RTE

I was not sure where the RTE aerial was receiving from, so just hooked the Colourkings (mux'ed at the masthead) cable to DTT box to try my luck.
The DTT box picked up 20 channels.It turns out that these channels are the UPC MMDS channels.RTE 1 was clear, all else scrambled.Also had full EPG etc.

Now the thing is, and i verified that, the MMDS cable is totally independant of the aerial cabling.
It appears that the MMDS signal is being somehow picked up by the Colourking aerial(s).Reflected/deflected off the MMDS Yagi perhaps ??

I am not getting any true DTT signal from the aerials which is fair enough they may be pointed at a relay and not Mullaganish.I can investigate that.
But is the interference expected ?
Apparently, since the MMDS Yagi went up the RTE reception has been poor hence the neeed to get RTE in the rooms not served by the MMDS.

Any input/suggestions would be gratefully accepted.
Thanks.

Apogee

It can't be reflected off the MMDS aerial because it's transmitted at ~2.5GHz. It must be bleed through from the cable after downconversion. At what frequency is the mux scanned in?

Sponge Bob

It could be an SCTV downconversion from a neighbour too .

Mike 1972

Perhaps a neighbour has diplexed the output of their MMDS converter into the same downlead as their UHF aerial and some of the signal is making its way into the aerial and being radiated

Apogee

Sponge Bob wrote: »

It could be an SCTV downconversion from a neighbour too .

SCTV uses DVB-S, not DVB-T.

glog

Thanks for your replies so far.

"At what frequency is the mux scanned in? "

Sorry, but I'm not really sure what you are asking here

The signal is definitely from UPC.It says it in 'Signal Info' on DTT box and also when i disconnect power supply feeding the MMDS, aerial then i lose signal on the DTT box.
I actually tried connecting the MMDS DVB-T box to the aerial cable and it's good enough to be getting full signal quality but i doubly confirmed that the Terrestial aerial and MMDS aerial are on 2 independent cable runs.
Would it be normal to see this much bleed through ?

Thanks in advance

STB

Sounds like one of these set ups.
http://www.boards.ie/vbulletin/showpost.php?p=62268794&postcount=109

What Apogee is asking you is what your local DTT mux is ....Presumably the DTT mux is from Mulaganish on 474 MHZ Ch 21 ?

maxg

glog wrote: »

Thanks for your replies so far.

"At what frequency is the mux scanned in? "

Sorry, but I'm not really sure what you are asking here

The signal is definitely from UPC.It says it in 'Signal Info' on DTT box and also when i disconnect power supply feeding the MMDS, aerial then i lose signal on the DTT box.
I actually tried connecting the MMDS DVB-T box to the aerial cable and it's good enough to be getting full signal quality but i doubly confirmed that the Terrestial aerial and MMDS aerial are on 2 independent cable runs.
Would it be normal to see this much bleed through ?

Thanks in advance

Bad shielded cables. The mmds signal leaks out at one cable and the other cable pick it up.

glog

STB,
It's very similar, it's actually one of these :
http://www.mycablebox.co.uk/index.php?main_page=product_info&cPath=38_74&products_id=87&zenid=b4ammttj7mg8n6vtp9r20fjqi0


But, let's not go there

Yes, it's Mullaghanish i was searching for, unsuccessfully as it happens, as i believe that the RTE aerial is pointed towards a relay in Crosshaven and not Mullaghanish.

The channels that were coming in on the DTT box were further up the range around 666Mhz and up (Ch45 i believe)