query re frequencies for funcub

[G3XJI]

Hi, as a complete newbie to satellite working, can someone please help.
Whilst I understand the up and downlink frequencies, I still hav'nt got my head round the procedure, If I am receiving a cq call on the 2metre downlink, say 144.960, what frequency the calling station be using fos his uplink transmission on 70cms, ie what frequency would I need to transmit on to reply?
Any help will be much appreciated

Regards.........G3XJI

[AussieSusan]

Have a look at the specs at http://amsat-uk.org/funcube/funcube-cubesat/ .

Basically it is an inverting transponder which means that a signal received at the top end of the uplink will appear at the bottom end of the downlink. Also note that the referenced web page shows that the uplink is LSB while the down link is USB - which makes sense for an inverting transponder.

By the way, you should not be hearing a signal on 144.960 - I will use 145.960 instead and for now ignore the doppler shifts which you can take into account as needed for yourself (as you would with any satellite work).

You will note that the frequency range of the uplink is 20KHz - from 435.130MHz to 435.150MHz - as is the downlink - from 145.950MHz to 145.970MHz. Therefore, if you are hearing a signal on 145.960MHz, subtract 145.950 (the bottom end downlink frequency) from it and then subtract that figure from 435.150MHz (the top end uplink frequency); 145.960 - 145.950 = 0.010; 435.150 - 0.010 = 435.140MHz.

To choose a frequency that does NOT happen to be in the middle of the passband: if I hear a signal on 145.955 then... 145.955 - 145.950 = 0.005; 435.150 - 0.005 = 435.145MHz.

Of course you need to be aware of the deviation of the signal and so avoid the bottom end of the uplink so that you do not transmit out of "band" of the satellite.

Susan

[G3XJI]

Hi Susan, many thanks for that, much appreciated. My reference to 145.960 was just an example which I chose because it was the centre of the downlink segment.
So thanks again for your help.
73......Allen

[G3XJI]

Whoops....just spotted the typo on my original message.....I entered 144.960 instead of 145.960, sorry for the senior moment.
ALLEN