We can use Einstein’s explanation of radio to help with satellite working. Einstein explained radio thus
"You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat. "
Had satellites existed when he lived he would have added…
“With satellites you have 2 cats, one for up and one for down that you need to point into space. Pointing cats is very difficult and makes satellite working difficult. And of course, like domestic radio, there are no cats.”
So it is just like ordinary radio with more cats that don’t exist and also cat pointing difficulties. Es’Hail 2 helps us with the cat pointing by not moving about the sky unlike the cats which would be very annoyed if you tried to point them and would move and squirm a lot. If they existed which they don’t.
My current thinking is that something like a Lime SDR Mini or Pluto SDR might be the way to go. They could do the 2.4 GHz TX (need amplifier of course) and the RX direct from the LNB IF. The free SDR-Radio software seems to do everything that is required. It does mean that the station requires a laptop though.
Yes, ADALM Pluto seems the best option to me too. However, it also needs an external 40MHz clock reference as the onboard one is pretty bad. GPSDO, OCXO or even the homebrew programmable OCXO kit from Qrp-labs should do.
Plus some filtering for TX before the amplifier, either a 2.4GHz SAW filter or something like this:
A typical good TCXO short term stability can translate to a worst-case drift of about 5Hz/sec at 2.4Ghz, if my math serves me right. I think with careful construction and if operating in constant temperature they could be fine.
OCXOs are 1-3 orders of magnitude better, but are a bit pricey (about £100 new) and the 40MHz ones aren’t that common on the used market. The common 10MHz ones are cheap and can be used with some software/firmware modification - I know there was some talk about this but I can’t find the link right now, to see if anyone managed to do it.
Showing my ignorance here…
Is the LNB actually a down converter (I thought LNB meant low noise booster, ie. just a preamp)? So is that stable enough and good enough LO purity to deal with an ssb downlink signal?
Which part of that generates your uplink on 2.4 ghz, is that the Pluto SDR? And is the wifi amp good enough linearity for ssb? I looked at a 2w wifi amp some years back, an 8 watt option is a big improvement…
On modern LNBs you get an integrated feed horn, 2 inputs (horizontal / vertical), an IF oscillator, mixer, IF amp/cable driver. Supply voltage picks one of the inputs and on many, superimposing a 22kHz tone on the power switches the oscillator IF so you can cover more band.
They have prodigious gain and the cable driver will drive the IF (about 700-2000MHz) over 50-100m of cable with ease.
An LNB (as opposed to an LNA) downconverts - in this case from 10.5 GHz to 740 MHz (approx). This, together with the amplification, allows cheap co-ax to be used from the dish focus to the receiver. There are two types of oscillators used in LNBs, Dielectric Resonator Oscillators and Phase Locked Loops (locked to a crystal). The later type provides adequate performance for SSB/CW.
The Pluto can do the IF RX at 740 MHz and the TX at 2.4 GHz (both simultaneously). It has a 40 MHz TCXO which is useable on CW and SSB but is not great.
I suspect WiFi amplifiers have to be linear to cope with the complex modulation used in WiFi (but I’m guessing). The “8 Watts” should be taken with a large pinch of salt I suspect. The amp has to be slightly modified to override its TX/RX switch. See amp below.
It’s probably valid when the device is used as a Wifi amp as it will be switching between TX and RX very fast, the peak power maybe 8W. It is extremely unlikely it would do 8W at 100% duty cycle. I read about this just recently but due to the rapid onset of age related befuddlement I cannot remember where.
He would most definately pointed out that understanding relativity as key to SAT work. Its as a near a perfect example, time dialation for GPS, Not to mention a moon bounce.
To see and play with things like this make me happy, which is why I got a radio licence.
The “8W” WiFi amplifier uses two YP242034 devices which are rated for 34dBm each (P1dB). The pair is good for 5W+, but people have been reporting getting from less than 2W to over 6W from them. I think the internal DC-DC converter should be investigated if the output is low; nominal is 6V but some people have reported it dropping down to 5.6V or less under load.
