Nice to see a variety of ATV signals through the transponder over the last few days since I got my first RX setup working. So a question for those that have transmitted through the bird.
The only real reference I have found to how much power I have to aim for is the statement
"S-Band 2.4 GHz WB-Uplink (DATV):
– wide band modes, DVB-S2
– peak EIRP of 53 dBW (2.4m dish and 100W) required
– RHCP polarisation"
This 53 dBW (100W with 2.4m dish) - is this for 2MS/s ? If so what power/dish is required for the narrower modes, like 333kS/s etc ?
Thanks for any help with this
The figures that you referred to were to fill the full 8 MHz of the transponder. Using less bandwidth (lower SR) needs much less power.
I hope to be able to issue some more comprehensive guidance soon, but if you extrapolate from my current parameters:
20 W at feed
gives 6 dB MER when received on a 1.2m dish
Double the dish size and you would need a quarter of the power. Double the SR (so double the bandwidth) and you would need to double the power.
If you extrapolate from this to a 2.4m dish and 100W, it would enable 5MS SR which would occupy 6.75 MHz - not far from the 8 MHz assumed in the original statement that you quoted.
Hope that helps
Now I can ask some more.
Is anyone using a helical aerial (easier to hide in garden)
I suppose that will need more power ?
As I am building for Oscar 100 only can I ignore the
8 Way switch and decoder ??
I can sort out ptt optocoupler myself
Is the amp on switcher there to compensate for insertion loss in switcher IC ?
I know that many people are using helicals for SSB and CW, but not sure that they have enough gain for DATV. It would be worth you comparing achieved helical gains with the gain of a 1.2m dish.
You can ignore the 8-way switch and decoder, but the amplifier on the 8-way switch does provide some useful gain in addition to compensating for the small insertion loss. You will only get about 1mw (0dBm) out of the Lime Mini at 2.4 GHz, so it depends what your PA needs to drive it.
The gain on a 1.2m dish of 2.4 GHz is at best 27 dBi.
A 67 element WiMo yagi has a gain of 22 dB. Four of them combined would be a potent an uplink. You lose 3 dB on circular but the array could also work terrestrially.
between summer house and shed ( I have power already there).
Re 8 way switch I think I will have to build Amp part at least
I need power to go down 25 meters of coax to garden
unless there is a commercial amp available in UK.
Can I use 5v from the usb hub that powers Lime mini
that way I don't need 12v psu and 8v regulator ?
Where does filter go ?
Too many questions in one post!
Unfortunately, you can't run the 8-way switch from +5v. We tried that on the first batch and had to modify them to run from 8v. The issue was that the amplifier is thermally unstable when run from 5v.
Filter positioning depends on your PA. If your PA needs an extra output filter, then that's where it should go. If not, it does not matter whether it is shack end or garden end (unless you are very close to a mobile phone tower, when you might need it garden end to prevent cable pick-up getting into your PA).
Just writing an article for CQ-TV about PA options. Should be published in 2 weeks or so.