SatSig topic:

Long distance IFL

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Feb 25^th, 2010 at 4:17am

Hi,

What is the best configuration for connection between iDirect Hub and Antenna for a long distance one, let say 500m to 1 km? I mean, is it using a FO converter or L-band to IF converter or any other ? I have iDirect 5IF chassis and 4.5m Suman Antenna.

Thank you

Feb 25^th, 2010 at 7:27am

Hello,

For 500-1000m the best option will be FO.

Feb 25^th, 2010 at 7:30am

Hi Oasis Network,

Do you have recommendation for the L-band to FO converter?

Feb 25^th, 2010 at 2:14pm

I have some experience with foxcomm system; it requieres some complicated AGC calibration but once it is set it works very fine.

Feb 25^th, 2010 at 7:11pm

Here is another possible supplier for L band fibre optic IFL link equipment:
https://www.emcore.com/fiber_optics/satellite_microwave/satellite_transport

Setting the levels at the inputs (both ways) is important. Avoid intermdulation noise by not setting too high. Avoid the noise floor by not setting too low. Discuss your application with the manufacturer to determine suitability for your application and maybe seek their help with setting up levels.

Best regards, Eric

Feb 26^th, 2010 at 1:03pm

Oasis, Eric, Thank you for your answers. It semms to me this is the best solution for long distance IFL. but, in my understanding, there will be a MOD/DEMOD process using this option, right? if there is, what about additional modulation error come from the RF to FO conversion and vice versa? is it significant to the link performance?

Regards

Feb 26^th, 2010 at 2:13pm

The L band (radio) signal in the coax cable is used to amplitude modulate the laser light, so there is a modulation and demodulation process. There is essentially just a single component at each end: laser at transmit end and light sensitive transistor at receive end. Some clever DC power AGC is needed for the laser to keep the light constant regardless of temperature and time.

Getting the L band input level correct is the key to getting satisfactory operation.

Too low and you will get too near the noise floor and your receive C/N will degrade or you will transmit wideband noise, interfering with everyone on the satellite.

Too high and you will get intermodulation noise. On the receive side this causes all the TV carriers, plus your wanted receive carriers etc on the L band to all mix up with one another. On transmit, if you radiate 2 (e.g. A and B) or more carriers you will radiate 3rd order intermod products (e.g 2A-B and 2B-A) either side which will interfere with other people. Ideally you want to monitor your BUC output using a high loss cross-waveguide coupler and check your transmit spectrum for any spurii.

The tricky bit is probably the receive side where you may have perhaps a hundred simultaneous carriers, across the whole of L band, so that the total aggregate power far exceeds the power of your wanted tiny return link burst carriers. The problem is keeping the total aggregate power under the intermodulation limit while keeping your wanted bursts from the remote sites well above the noise floor.

You will need adjustable attenuators on tx and rx at the antenna site.

Get advice help from the manufacturer.

Best regards, Eric.

Feb 26^th, 2010 at 5:41pm

Well..it's getting clear now. Thank's for the explanation, Eric.

Best Regards

Apr 14^th, 2010 at 12:26am

Pulse Power Measurement out of the UK makes a product called ViaLite. We saw them at Sat2010, and will be getting a demo shortly. That is the [superlative deleted by forum admin] product that we've been able to find.. don't know if it works well yet.. But intelsat uses them for most of their Teleports.. Wink

Added by forum admin: Link: RF over optic fibre by ViaLite

Apr 15^th, 2010 at 11:48am

Wish I would have known you were going to be up there. I was there for the first two days of vendor exhibits (Tuesday and Wednesday). We could have had a beer...

Apr 23^rd, 2010 at 12:00am

I was thinking about calling you actually..! Are you going to Interlink?? It's been a while since we talked, drop me a line sometime so we can catch up.. I've actually got some new things in the pipeline this year