Actual power needed for Es'hail-2 ATV

Latest News and Discussion about the use of the DATV transponder on Es'hailsat 2
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g7jfi
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Joined: Thu Sep 29, 2016 4:31 pm

Actual power needed for Es'hail-2 ATV

Post by g7jfi » Sun Mar 10, 2019 6:28 pm

Hello everyone,

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
Terry G7JFI

G8GKQ
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Re: Actual power needed for Es'hail-2 ATV

Post by G8GKQ » Sun Mar 10, 2019 10:56 pm

Terry

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:

1.2m dish
250KS DVB-S2
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

Dave, G8GKQ

g7jfi
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Joined: Thu Sep 29, 2016 4:31 pm

Re: Actual power needed for Es'hail-2 ATV

Post by g7jfi » Mon Mar 11, 2019 10:17 am

Hi Dave,

Thanks for that info, it's exactly what I was looking for!

Cheers
Terry G7JFI

G8HKN
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Joined: Mon Jan 21, 2019 4:04 pm

Re: Actual power needed for Es'hail-2 ATV

Post by G8HKN » Mon Mar 11, 2019 2:52 pm

Thanks for asking that Terry
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 ?
Roger G8HKN

G8GKQ
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Re: Actual power needed for Es'hail-2 ATV

Post by G8GKQ » Mon Mar 11, 2019 3:04 pm

Hi Roger

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.

Dave, G8GKQ

g0mjw
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Joined: Sat Sep 20, 2014 9:15 am

Re: Actual power needed for Es'hail-2 ATV

Post by g0mjw » Mon Mar 11, 2019 5:11 pm

Not sure a helical is a good idea (never built one) but an array of yagis would work and can be phased for RHCP.
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.

Mike

G8HKN
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Joined: Mon Jan 21, 2019 4:04 pm

Re: Actual power needed for Es'hail-2 ATV

Post by G8HKN » Tue Mar 12, 2019 4:27 pm

Thanks it looks like it's going to be 1.2M dish
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 ?
shack end
garden end
after PA
73 Roger

G8GKQ
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Re: Actual power needed for Es'hail-2 ATV

Post by G8GKQ » Tue Mar 19, 2019 2:21 pm

Hi Roger

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.

Dave

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