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Comag Porty
menu»Digital
RECEIVING DIGITAL ATV

The Freeview or DVB-T boxes are not suitable for receiving digital atv as the format is entirely different. However DVB-S digital satellite boxes might be useable but only if they let you drop the symbol rate from around 22,000 to 4000 . Most of the sat boxes do not let you set this value. The Sky Star2 and Haupage pc cards both allow full range of settings. If there is a digital repeater near you, you should be able to get the settings from their club or website. We currently transmit a symbol rate of 4000 with FEC of 3/4 on 1304Mhz. These details might change with a move to Pokesdown site.

UNDERSTANDING Digital tv
As with computers there is a load of jargon to get used to with digital tv.With your internet connection the speed of the connection is dependent upon the quality of the link.
If there are lots of corrupted data the remote computer will request a re-send of the affected block of data, this slows the maximum acheiveable speed of transfer.
When transmitting data on a transmitter there is no return path available for the receiving equipment to request a resend, so the data has to be error corrected before sending, or Forward Error Corrected.(FEC). The proportion of correction to data (error correction can use up quite a large chunk of each block of data) is expressed in a ratio of the number of bits out of the coder to the number into the coder, e.g. 1/2 and DVB-S uses a complicated algorithm called the Viterbi code . 1/2 would be used where system noise could be a problem, i.e. weak signals.
Why Megasymbols? Different transmission formats use different sizes of data, bits or bytes etc so by calling the data symbols it gives a more useful way of comparing speeds.
I will be adding to this page as time permits.


The slimline mains-only SL55 with Svideo option and Lock light or the more chubby Porty with mains/12v dc option.PORTY Both are remote control and can either receive DVB-S on a standard LNB or can use a modified LNB for 10Ghz. By connecting directly to a preamp and a 23cms aerial instead of a LNB they work well on 23cms.

The SkyStar 2 PC card receiver is fine if you prefer to incorporate it into your computer with a PCI slot.

This does not apply to the SL65. Remember to isolate the dc that powers the lnb before connecting your 23cms aerial. Because the original boxes used a lnb with amplifier at the dish it may be necessary to insert a pre-amp which can be powered from the box. To adjust your Comag box, select MENU then Installation. Select option 1 Antenna Setting. Default password is 0000 . Find a spare Satellite Name to modify.eg NileSat. Change the transponder settings (right arrow, scroll up/down the list of frequencies to NEW TP option press OK). In sub-window on Frequency type in 11304, Symbol rate 4000, FEC auto. All other options -off. Polarity -doesnt matter.Press OK to go back to left window. Down arrow to highlight LNB FREQUENCY. Right arrow scroll up/down to USER DEFINE setting in right-hand window. Press OK and type in 10000 . Press OK to save data. DiSEqC =Disable. Motor=Disable (Other options not used because there is no lnb connected but the dc voltage feed may be useful if an aerial pre-amp is used).When a signal is available select the bottom option..Start Search Satellite. The station ID (GB3SQ) should appear in the left white window if it has found the signal ok.These boxes do not memorise the settings unless a signal is present. Use the exit button twice to return to received screen and press INFO button to check settings are correctly stored. Align aerial for max strength. You may need to get over 50% strength to register the channel, depending on preamp noise. Remember there is no halfway house, if there is sufficient signal you will get a P5 picture, if not you will probably get nothing, so persevere.Use the info button to get maximum signal levels.These boxes are designed to work with a LNB in front so will almost certainly require a hi-gain preamp unless you are within sight of the repeater. Press MENU select ' 2 Service organising' press ok. Press option 5 'Edit TP list' press ok. select 1 Satellite list. Press ok. In small blue window select ADD. press ok twice. NEWSAT will appear as last entry in list. Highlight it, press ok. select RENAME. enter letters required e.g. REPEATER then move to OK option & press ok. select MOVE option press ok; press ok for '1' which takes it to top of the list. Use option 1 'Edit Channels' to move it to top of Favorites list. Exit to finish. Put the kettle on.
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