BATC Forum

Hi all

This maybe sound a daft question, but what is the channel spacing when using a Sat Rx ,
ie. if the lowest frequency it tunes to is 950MHz, what frequency will the lowest channel be ans what spacing to the next.
I don't want to build a down converter for 13 cms and find a channel misalignment, and unfortunately the tuning step size is not given
apart from the IF bandwidth of 55 MHz and 8MHz < 5MS/s., which would imply the tuning step is 8MHz , or is it ??

As soon I can find out I can build up a G3WDG 2.4 GHz converter that was popular when AO-40 was alive and change the LO to give an output
somewhere between 950 MHz and 2100 MHz.

Also , how much gain will I need to put in front of the Sat Rx to make it usable, ? the average LNB has 50dB. Remember I'm miles from most activity in deepest Shropshire, but I'm well sited from NW thru SW , 600'asl

Thanks
Richard G8JVM

Oh well I'll reply to myself .
If someone would check what I think might be the answer
bog standard Ku band LNB range 950 -2110 ish
taken from Astra 2D 10.700 GHZ - 12.75 GHz
lowest bearer at 10.714 GHz , bearer spacing 15 MHz up to 11.7195 GHz, then from 11758 GHZ to 11.11.876 GHz 20 MHz spacing a gap then 20 MHz spacing from 11.914 GHz up.
The LCD is 5 MHz, LNB LO =9.750 GHz Lowest IF Rx Freq = 10.714 - 9.750 = 0,964 GHz lowest IF freq.

xtal included in the G3WDG040 down converter is 94 MHz x 12 =1128 MHz 2440MHz -1128 = 1312 MHz , Nearest bearer ( 11067 - 9750 ) = 1317 MHz
Difference between 1312 MHz & 1317 MHZ = 5 MHz.
I'm guessing the LO frequency step in the Sat Rx is 5 MHz as that is the LCD.

Can someone please either confirm I'm correct or tell me what is if I'm wrong, as I'll be looking for a very weak signal, as I think BH is the nearest operational digital repeater to me here in Telford.

thanks
Richard g8jvm

Hi Richard,

Digital sat receivers tune in 1MHz steps, you just dial it in, tuning a couple of MHz away from a 1Ms signal causes no decode so it seems to be correct even if it is 8MHz bandwidth filtering...

Rob

Many thanks Rob.
Its shack tidy time tomorrow to find the circuit for the down converter and build it up.
I'm adding an extra relay in the receive path going to the DB6NT 13 cms transverter, after the antenna change over relay
to divert the receive path to the down converter, which will also be at mast head. Set it so the relay is on the main +12V feed to the
transverter, so when no power is sent up to the transverter the Rx is switched to the down coverter, and when power is applied to the tranverter
the relay is energised and the path is to the Rx input of the transverter.
I can use cheap RG6 coax down to the shack . I may be able to put 20dB of LNA after the down converter at masthead. Space in the enclosure ??

73
Richard G8JVM