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125k Offset For Sx


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#1 clipper

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Posted 26 August 2011 - 09:03 AM

Wondering if anyone has experienced needing to apply 212625khz as input frequency for SX. Using wideband antenna, almost LOS, DCP 76dbuv, BER's and MER couldn't be better at outlet ( after replacing cabling and wall plate)- new Samsung LED refused to find SX. Attenuated 12db still no find. Decided to try 125k offset and bingo! Suspect spiking noise ch 0/1, but didn't confirm on meter at the time. Customer didn't want a new antenna and problem seemed fixed with the offset solution. I've seen similar probs with WIN off wideband antennas but not from MUX 10.

#2 lizclinton

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Posted 26 August 2011 - 12:53 PM

Wondering if anyone has experienced needing to apply 212625khz as input frequency for SX. Using wideband antenna, almost LOS, DCP 76dbuv, BER's and MER couldn't be better at outlet ( after replacing cabling and wall plate)- new Samsung LED refused to find SX. Attenuated 12db still no find. Decided to try 125k offset and bingo! Suspect spiking noise ch 0/1, but didn't confirm on meter at the time. Customer didn't want a new antenna and problem seemed fixed with the offset solution. I've seen similar probs with WIN off wideband antennas but not from MUX 10.

From memory the ABC on channel 8 also has a similar offset which used to play havoc with the first Thomson STB's way back in 2001. Oddly the same offset also applies to the Northern suburbs translator at government hill on UHF band 5.

#3 alanh

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Posted 26 August 2011 - 08:26 PM

Clipper,
Mt Wellington
TVT7 184625 kHz
ABT8 191500 kHz
SBS9A 205500 kHz
TNT10 212500 kHz
TDT11 219500 kHz

Government Hills RISDON
ABT56 725375 kHz
TNT62 767500 kHz
SBS64 781625 kHz
TVT65 788500 kHz
TDT66 795500 kHz

Single Hill Cahill Place ACTON
SBS35 578500 kHz
ABT36 585500 kHz
TVT37 592500 kHz
TNT38 599500 kHz
TDT51 690500 kHz

cnr Blatherwick Rise & South-Arm Rd OPOSSUM BAY
TVT39 606.500 kHz
TDT41 620.500 kHz
SBS42 627625 kHz
ABT45 648625 kHz
TNT48 669500 kHz

All horizontally polarised

Mostly receivers automatic fine tuning should be able to cope with the offset particularly if the receiver conforms to the Australian Standard for digital receivers.
Note that Mount Wellingto will permanently remain exclusively band 3 horizontal. All transmitters on Government Hills Risdon will have to change channels to below channel 51 in 2013 or 2014. Once analog is switched off the 125 kHz offset will not be needed.

AlanH

#4 clipper

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Posted 26 August 2011 - 10:35 PM

Mt Wellington
TVT7 184625 kHz
ABT8 191500 kHz
SBS9A 205500 kHz
TNT10 212500 kHz
TDT11 219500 kHz


My query concerned an offset for TNT10. If WIN 184625 is an assigned offset needed to counteract 'spillover' effects from WIN 6 analog, then that accounts for several complaints I've heard from people losing audio off WIN digital(tuned at 184500). Change to WIN and no sound... change to another Mux and back again and sound returns- that sort of carry on. Can't recall the model/brand of TV they had.

#5 alanh

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Posted 27 August 2011 - 01:41 AM

Clipper,
Your problem is not the offset, but interference from FM radio.

In overload situations harmonics are generated. This also is made worse by corrosion in the antenna.

TNT (Southern Cross) RF channel 10 212.5 MHz
7SBS 105.6 MHz x 2 = 211.2 MHz - 212.5 = 1.1 MHz and is the strongest FM signal
7HFC 106.5MHz x 2 = 213.0 MHz - 212.5 = 0.5 MHz
7XXX 107.3 x 2 = 214.6 MHz - 212.5 = 2.1 MHz
All of these interfering signals are within channel 10

As you can see there is no 125 kHz offset, you are just trying to get away from the interference.

TDT(Network 10) RF channel 11 is 219.5 MHz
7XXX 107.3 x 2 = 214.6 MHz. Which is just above channel 11 so the effect is less.

Since UHF will not be used for any digital signals from Mt Wellington. So replace the antenna with a band 3 only antenna. It is much less sensitive to 106.5 MHz and with no corrosiion.

The replacement of the antenna should be sufficient, however if it is not put a GME Kingray FL3-BPMH filter set to only pass band 3 in the antenna cable as close to the receiver as possible but prior to any splits.

Note the interference will not be improved by filters or attenuators if there is corrosion in the antenna.

You should also find that the MER is less than the C/N particularly on RF channel 10.

For a list of the appropriate antennas. Click on the H3 link in Get the best reception - Hobart

Wideband antennas are sensitive to unwanted inferference and impulse noise and less sensitive to the channels you are trying to receive.

AlanH

#6 clipper

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Posted 29 August 2011 - 12:08 AM

replace the antenna with a band 3 only antenna. It is much less sensitive to 106.5 MHz and with no corrosiion.

The replacement of the antenna should be sufficient, however if it is not put a GME Kingray FL3-BPMH filter set to only pass band 3 in the antenna cable as close to the receiver as possible but prior to any splits.



Appreciate what you've said Alan- I believe the customer was quite happy with a 125k offset "fix" at no cost.

#7 Tazzy2Heads

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Posted 30 August 2011 - 05:37 PM

Wondering if anyone has experienced needing to apply 212625khz as input frequency for SX. Using wideband antenna, almost LOS, DCP 76dbuv, BER's and MER couldn't be better at outlet ( after replacing cabling and wall plate)- new Samsung LED refused to find SX. Attenuated 12db still no find. Decided to try 125k offset and bingo! Suspect spiking noise ch 0/1, but didn't confirm on meter at the time. Customer didn't want a new antenna and problem seemed fixed with the offset solution. I've seen similar probs with WIN off wideband antennas but not from MUX 10.

Hi 'clipper',
Haven't had any tuning problems yet with CH 10 212.5Mhz that are fixed by tuning to an offset frequency, but who's to say whats over the next hill.
The only gadgets that manually tuning in the offset for CH7 WIN 184.625Mhz helped in bad areas I found were the SD Pheonix and Healing and their generic
brands STB's and the odd tv., which you already know about. Not sure whether FM harmonics is a big issue down here in the domestic house type installation as most DIY's have had FM interference for years on there anologue tv's and vcr's and don't know what it is and have put up with it. These same DIY's have all gone out and bought Set Top boxes and now new tv's and the tuners seem to be able to cope ok most of the time, even with half an old vhf antenna, a plug in booster and crap cable picking up everything from DC to Daylight with line of sight to the towers and 85-90+ db signals.

Cheers Tazzy.

#8 clipper

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Posted 01 September 2011 - 10:27 AM

Hi 'clipper',
Haven't had any tuning problems yet with CH 10 212.5Mhz that are fixed by tuning to an offset frequency, but who's to say whats over the next hill. Agreed, first time I've come across it. Pretty sure a Band 3 antenna would have been happy with 212500 but we didn't go down that path.


The only gadgets that manually tuning in the offset for CH7 WIN 184.625Mhz helped in bad areas I found were the SD Pheonix and Healing. Yeah, used to install these all the time. Still carry around a Phoenix for the odd time that my meter won't lock on, to show customer the BER levels and that the Phoenix maintains a solid picture, compared to their TV which is constantly stuttering. In that case I tell them to get a Panasonic as these seem to be able to process high BER levels and maintain picture.


Re- WIN offset, some TV's/ PVR's don't appear to erase the channel list on performing an auto search and will ''compare' the found channel with the one already stored. Keeping the stored one if the PIDs are the same. When I did this with a PVR we ended up with WIN LCN 8 ( no good) and WIN LCN9 ( good with the 125 offset.) Couldn't manually erase just WIN and manually rescan, and I couldn't risk a factory reset with all the files on the HDD. Customer actually preferred LCN 9, corresponding to the network.