MMDS (2.5Ghz) DTV TRANSMISSION QUESTIONS

netchip

Hi,
Living in SENEGAL, a friend of mine diffuses about 100 Channels of Digital TV in the MMDS band. As expected some areas are of bad reception as the Transmitters are only 25Watts HF.
So I did get an Idea , being an EX-Radio HAM (GWPTH) I am famillier with HF and UHF propogation.
So this is my (Very high) technical question !
Instead of puting up relay stations to boost up the MMDS signal in bad zones (Which will boost the signal of all the diffusers and this we do not want to do as the Transmiters are on the same site) I was thinking of using the combiner signal, On the combiner there is a ''test'' output BNC with about 15 Watts HF containing all the transmitted channels. If I take this output and feed it into a DISH ? As the main transmiter has 360° transmitting antennas this should give me a highly directionel ''BEAM'' which i should be able to pickup in the Bad reception area ! where the main signal is too low ! and re-amplify to furish our clients a better signal (pointing their antennas in the booster transmitters direction of course.)
AND as its the same signal no delais, no echos would be seen !
Anybody out there who can help me on this question !!!!

ralphmagno

hello,i am not sure what you are trying to do.
how far are you from the 25 watt transmitter.
are they on a hill side or a mountain??
if this is just for you there are mmds at 2.5 ghz high gain antennas and pre amps all over the place.
25 watts at 2.5 ghz should give you about 25 miles 40 kms.
if analoge and more if digital.
i work with 10 .660 ghz mmds equilivant in digital with 1 watt.
using an satellite lnb and moving the lo by 90 mhz a mormal satellite receiver will now tune and lock on no problem.
using a 30 cm dish and it has a 20 kn range and with a 60 cm dish even more.
need more information on the system you have and what you are trying to do.
if you are trying to send this to others as well you can use a beam bender.
it is a mmds receiving antenna, an amplifier just for this use and another mmds antenna twisted to a different pol.
if you are receiving this vertically you want to send this horz.will need a lot more information.
ralph

Channel Hopper

Yes, a parabolic beam will amplify the signal in one direction, no matter if it is 2.5 GHz, or above.

You will however need to work out the correct spread design on the actual frequency used, and the delivery distance, otherwise you may run into issues with users receiving a drop of signal if they reside on the outer areas of your collection zone.

Remember as well, a 360 omnidirectional antenna also transmits upwards (admittedly at a reduced rate) and so the overall gain from a directional antenna will be greater in one direction at a terrestrial level with a correctly polarised VSAT antenna.

There is a very fine line between "hobby" and "mental illness"

netchip

Ok thanks for the reflections. I fact I am trying to put up a system that will eliminate the need to put the combined 100 channel signal into microwave links as the band width would be too small !! (need 300Mhz) So if I do take the signal from the existing feeder (combiner) it contains every single channel already ! By pushing this into an appropriate dish and head I should be able to recieve it in certain ''bad'' areas then with a large band send it to other people (The antenne will not have the save polarization of direction as the main TX) does this seem ''workable ''

netchip

The system is up on top of the highest building here in DAKAR ! There are two companys using the MMDS TV and (this is where its complicated) the other user has crossed channel TX) i.e. We use ch 13 he 14 we 15 he 16 etc etc etc So if we just recieve and re-transmit a whole range we will re-transmit HIS as well !!! which is NOT a good thing to do !! so If i get our signal just before the antenna feeder (on the output of the combiner) I should be able to direct this into one of the ''bad'' areas and re-boost it afterward.