I/Q Modulators and GHz SSB.

[CJay]

I've been looking around for a way to get myself onto QO-100/ES'Hail2 and of course it needs equipment I don't own.

Dish, LNB, patch antenna, GPS locked 25MHz reference is all fairly simple but...

My SSB capabilities run out of MHz at 30 so I either need to buy myself something or get creative.

I've bumped into some rather useful looking I/Q modulators* which look like they'd be a decent way to generate GHz bands SSB, of course I'd need something to create the baseband I/Q and a nice, clean LO source but I think they'd work.

I can use a sig gen for the LO to prove the concept, I can generate the I/Q with the Pi I'll be using to receive and demodulate from an SDR.

PA will probably be one of the 8W WiFi boosters, PCB design is likely to be a copy of the eval board for the chip.

So, what am I missing, what am I likely to trip up on?


*the AD8346 is the one that's occupying my thoughts at the moment as it's in a fairly friendly package and claims to be capable of operation up to 2.5GHz, there's even a handy download of the Gerbers for the eval board so the PCB requires no effort on my part other than a flex of the credit card.

[awallin]

I've been looking around for a way to get myself onto QO-100/ES'Hail2 and of course it needs equipment I don't own.

https://amsat-uk.org/satellites/geo/eshail-2/

does that mean Tx towards the sat is always on 2.4 GHz and Rx from the sat is at 10.5 GHz ?

for the lower frequency I'd use an USRP B210... not sure if there are cheap(ish) SDRs directly on 10.5 GHz...

[CJay]

I've been looking around for a way to get myself onto QO-100/ES'Hail2 and of course it needs equipment I don't own.

https://amsat-uk.org/satellites/geo/eshail-2/

does that mean Tx towards the sat is always on 2.4 GHz and Rx from the sat is at 10.5 GHz ?

for the lower frequency I'd use an USRP B210... not sure if there are cheap(ish) SDRs directly on 10.5 GHz...

That's pretty much it, uplink is 2.4GHz so there's a plethora of cheap parts and components intended for WiFi which can be put to good use.

Downlink is 10.5GHz, so a standard consumer grade KU band LNB and dish works just fine to downconvert into the range of a cheap RTL dongle and there's free open source software like SDR# or SDRConsole, the Ettus is an excellent bit of kit but so far out of my pocket it just can't happen unless I win one somehow.

Budget for this is as close to £0 as I can make it, sadly I've failed in that aim and RX so far stands me at £22 for the dish, a suitable PLL LNB and some bias tees.

I'm expecting TX to be ballpark £100 if I can get the I/Q modulator to work

[David Hess]

For a single I/Q modulator, the phasing method of SSB generation is used.  The complication is that not only do the carriers need to be 90 degrees out of phase which is easy enough to do for a single frequency, but the audio needs to be duplicated with one duplicate made 90 degrees out of phase at every frequency.  Amazingly enough, this is quite feasible in the analog domain with an array of RC networks and because of the precision required, audio quality is excellent.  Creating the quadrature audio signal can of course also be done digitally through the Hilbert transform.

[CJay]

Thanks David, the AD chips look like they implement the phasing method in silicon, much simpler for an end user to implement at GHz frequencies, I'm hoping I can replicate the eval board for now but have more ambitious plans for the future.

[Bicurico]

Hi,

Sorry to revive this old thread, but out of boredom and because I saw a video review of the Pluto+ SDR that showcased this application:


This got me interested in QO-100 reception.

I thought I already had most of the required equipment, but turns out, I don't:

- I have, among lots of other stuff, two practically unused ADALM Pluto (rev. B). But they lack the Crystal and PTT mod.
- I have several satellite dishes, but I understand that a special LNB with modded Crystal is needed for frequency stability.
- To upload, a 2.4GHz bandpass filter is obviously required, if the Pluto or similar SDR transciever is to be used. I don't own one.
- A 10W amplifier for 2.4GHz is needed. Don't own one, either.
- Not sure what antenna is used for uploading, I think this is what the helix with dielectric is all about, which I don't own.

Looking at different forums, websites and online shops, it is pretty easy to spend 500-1000 Euro for all required components, excluding the Pluto!

That just killed this project for me.

Still, I wonder that this can't be it. There must be a cheaper way, right? Anyone willing to enlighten me? I do have an amateur radio license, but I am not afiliated to any club nor do I personally know any other HAM.

I would be OK to mod one of my Pluto, to add a better OCXO and a PTT board (not sure where or what do buy - saw two eBay offers for this at 50 Euro combined, not exactly cheap) or even buy a Pluto+ from AliExpress (has better OCXO, 2x RX/TX and Ethernet, but lousy FW support). I would be willing to spend some money on a 10W amplifier, especially if it could be useful for other aplications).

Thanks,
Vitor

[Bicurico]

Update:

I made a test and guess what: I am receiving QO-100 with my existing gear!

I am using:

1) Emitor COMBOLOOK field meter (which I happen to have permanently setup for satellite dish tuning): this is powering the LNB.
2) A junk TV splitter (50-2450MHz)
3) A DC Blocker
4) Malachite SDR (Chinese Clone), connected to the TV splitter with DC blocker to protect from DC powering the LNB

Tuning to 739-741MHz reveals some action going on and using USB modulation I can perfectly hear people! Note: 10.490MHz is downconverted by the LNB with LF=9.750MHz, resulting in having the signal at 740MHz, which most SDR can receive. I used the Malachite SDR, but could have used a PC based solution with RTL, HackRF or Pluto and some software like SDR Console.

Of course, I know understand why a stablized LNB is recommended: every 10 seconds I need to adjust the frequency due to drifting.

But it works!

Conclusion: the absolute low-cost solution is to use a regular dish, point it to 26.0E and use a cheap sat-receiver with LNB-Through port. Attach a DC blocker to protect the radio and connect a RTL2832 dongle. Even if you need to buy all this, you will probably spend less than 50 Euro (dish = 15 Euro, LNB = 7 Euro, Sat DC Blocker = 3 Euro, RTL2832 dongle = 20 Euro). Of course, this only covers the reception and it will suffer from a lot of drifting.

Sorry, I thing this is really the wrong thread, though.

[ftg]

IQ SSB generation is perfectly possible on 2.4GHz. Eero, OH2BTG has made a QO-100 rig with zero-if SSB generation via the phasing method.
The modulator construction was borrowed from Juma TRX2 http://www.jumaradio.com/juma-trx2/.
IQ-modulator itself was some eBay module on a green pcb, so I'm unsure if it was ADL5375, which seems to be the one available now.
Local oscillator was an eBay ADF4350 module connected to a surplus 16.384MHz double ovened OCXO.

The IQ-modulator has very wide IF bandwidth, so filtering the SSB I and Q signals well is an absolute requirement.
A decent compressor for the audio also helps.

But ADALM-PLUTO or Pluto+ are likely far easier solutions, but require a computer.

But my own QO-100 rig is still a pile of parts