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Service Providers >> TooWay and KA-SAT satellite >> Tooway carrier spectrum in each spot beam ?
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Message started by Eric Johnston on Jul 28th, 2013 at 7:02pm

Title: Tooway carrier spectrum in each spot beam ?
Post by Eric Johnston on Jul 28th, 2013 at 7:02pm
http://www.tdcom.fr/tdcom/files/Presentation%20KASAT.pdf
says: 250 MHz per beam, 400 Mbit/s per spot beam

Can anyone verify, using spectrum analyser, what downlink carriers are visible in each beam ? What bandwidth are the carriers, how many carriers and are they on both polarisations ?

A 27.5 MHz wide carrier might carry 68 Mbit/s using 8PSK 5/6 FEC in clear sky conditions.

Title: Re: Tooway carrier spectrum in each spot beam ?
Post by Munger on Jul 29th, 2013 at 3:19pm
I have the dish/tria available. If someone in my area has a spectrum analyzer fancies driving over and plugging it in to see whats available....

Located near Cambridge, UK.

Title: Re: Tooway carrier spectrum in each spot beam ?
Post by Sudiste on Jul 30th, 2013 at 6:21pm
Hello
There is no polarisation on Tooway beams.

Title: Re: Tooway carrier spectrum in each spot beam ?
Post by Eric Johnston on Jul 30th, 2013 at 7:35pm
I am aware that KA-SAT uses circular polarisation.

Does the entire system use only one polarisation or does the polarisation change according to beam colour ?

The text below assumes that both circular polariations are used.

KA-SAT uses 19.7 - 20.2 GHz for downlinks to customers.

I understand that each spot beam uses 250 MHz, i.e half of the used band.

I'm assuming the system uses left and right circular polarisation (LHCP and RHCP). The TRIA has a polarisation switch that may be operated a number of times. NO adjustment angle amount is required. The wanted polarisation will either be received perfectly or not at all. This makes installation much easier compared with linear polarisation, which requires both selection of polarisation also rotation angle adjustment, depending on location. The automated carrier acquisition process can change TRIA polarisations and sweep probable carrier frequencies looking for a good signal.
There are 4 colours of beams and you need four colours to cover a map with no two adjacent beams the same to avoid interference.

I think there are two beam polarisations:
RHCP and LHCP.
I think there are two different, non interfering, frequency plans, each using half of the available range, 19.7-20.2 GHz
Most likely they interleave 12 x 30 MHz carriers across the 500 MHz, with 6 assigned to each frequency plan. We will see. It would make the satellite output multiplexer design possible to have the carriers spaced well apart, rather than packed adacent to each other, in two 250 MHz blocks.

If you look at a sniff off the IFL cable and look at the band 950 - 2300 MHz I would expect to see carriers in the ranges:
950 - 1700 MHz Receive (downlink) carriers. Probably 6 carriers per beam, each approx 28 MHz wide.
1800 - 2300 MHz Transmit bursts, narrower TDMA bursting carriers, about 3 MHz wide.  Such a carrier will only be visible when the site transmits a burst.

All above is speculation. I am interested to see if the full capacity is actually yet provided.

Any spectrum measurement plots welcome. Take care to avoid blowing up your analyser by getting DC to the input, or damaging the Tooway equipment by short circuiting the power in the IFL cable.  A high loss coupler with DC block is recommended.

Best regards, Eric


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