My Portsdown Conundrum - Actually a MiniTiouner Issue!

[g0mgx]

Hi All,

Is anyone willing to have a look at this blog post of mine:

https://g0mgx.blogspot.com/2019/04/a-po ... ndrum.html

and then let me know if you can see what I am doing wrong.

I first test the Portsdown MiniTiouner combination at 146.5MHz and all is perfect; change to 2407.75MHz and I can't resolve the picture any more.

Very confused!

My TX settings:



I'm sure the round circle in the constellation is telling me something - dont know what though



Many thanks

Mark
G0MGX

[G7JTT]

Try changing to DVB-S2 , H264 and animated testcard and see if that works.

John

[g4hiz]

A couple of points. The frequency as listed on the tab is 407.75MHz are you sure that you are not transmitting on this frequency rather than 2407.75MHz ? Try 2407MHz instead to check output in this band, it worked for me. Second point, the 1MS/s symbol rate can sometimes produce a flaky output (Pi straining, I believe), try a lower symbol rate, say 500kS/s.

73
Jen

[g0mgx]

The "2" on the frequency selection is just off the button display but is 2407.75.

I've just stepped up the frequency (with an SR of 333) and the constellation gets more round on RX as the frequency increases - it works up to 2140 MHz but at 2150MHz.





I've removed the wi-fi booster and just have the LimeSDR output connected to a patch antenna.

Is anyone else able to reproduce?

Mark

[G8GKQ]

Hi Mark

I was going to suggest exactly this - checking at what frequency it failed to lock any more. The problem is poor phase noise performance of either your LimeSDR Mini or your MiniTiouner. Until we know which, it is difficult to progress further.

Do you have any other transmitters that you can test your MiniTiouner with at 2400 MHz? Or any other (known good at 2400 MHz) receivers to check the Lime with?

Do the sysmptoms go away if you leave the LimeSDR Mini running (as it heats up internally)?

The problem with the frequency overspilling the display button acknowledged - I've added it to my to-fix list!

73

Dave, G8GKQ

[g0mgx]

Hi Dave

I don't have another RX hare, but I know a local ham who has a MiniTiouner I could no doubt borrow.

I will leave the Lime in TX for a while at 2150 MHz and see if it locks after a while and report back on both scenarios.

Mark

[g4eml]

Looks like the phase noise is getting worse as you increase frequency.
My Lime is much worse on 2400 than it is on 437, I get a much better constellation transverting up to 2400 than I do generating it directly. Others have had problems on higher frequencies.

It could also be down to power supply noise, so it might be worth experimenting there. Noise could easily affect higher frequencies more than lower ones.

Or it could just be that some Limes are worse than others.

[G8GKQ]

Thanks Mark

I have observed that the phase noise increases with frequency (I had trouble with my hardware version 1.1 LimeSDR Mini at 3.4 GHz, but that improved as it warmed up on a cold and windy day on a hilltop), but it should not be this bad.

The spec is below, but I do not know of anybody with the equipment to check a unit against this spec.

Please let me know how you get on with your comparitive tests and then if required we will be able to support you in getting RMA authorisation from Lime Microsystems.

Dave, G8GKQ

[g0mgx]

Thanks Dave

I've just blown the dust of my Portsdown 2018 and tried that in the same set up with exactly the same results.

So we are concluding there is something amiss with my MiniTiouner?

Any thoughts on debugging this further or what to try would be very welcome.

Mark
G0MGX

[g0mgx]

This is all connected to the PSU for the MiniTiouner.

I have a buck-boost on the board to drop the supply DC down to 4V which then feeds the on-board regulators.

I have added a jumper J3 to provide the supply DC to F socket A to power my LNBs when connected - and the higher the supply voltage the more ripple on the output of the buck boost and hence the lower the maximum usable frequency on RX.

I was happily running the MiniTiouner on an 18V DC feed to put my LNB connected to F socket A into the correct polarisation to RX es'hail-2 - which was working fine!

How do others power the LNBs - separate PSUs for the MiniTiouner and the LNBs?

Mark
G0MGX