Help please, funny signal from Portsdown 4

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Basil
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Joined: Tue Sep 10, 2013 7:28 pm

Help please, funny signal from Portsdown 4

Post by Basil » Thu Apr 28, 2022 8:25 pm

I find myself in need of help please!

I just erected a new dish and have it set up and hearing narrow and wide band signals OK. I am using SDR Console for the narrow band SSB. Both RX and TX, to a Pluto via LAN / USB, with the Pluto at the dish. All worked well with my old dish, albeit a rather weak DATV signal out.

The Pluto feeds an AD pre amp via a small attenuator (10dB from memory) and this in turn feeds a 20W SG Labs amp. The SG Lab amp feeds a POTY at the dish via about 12 feet of LM400.

I was initially able to see my tone and tune signals from SDR Console on Goonhilly and they looked fine. I then tried to send a test card from my PD4 and watched for the signal on both my MiniTiouner and on the web quick tune software. I was alarmed to see 2 seconds of a normal signal then it broke up and showed not as 333 kS/s but as 1500 and then 2000 at a low level. I didn't want to spend long sending iffy signals, but using 250 kS/s did the same. 2 seconds of OK, then break up and bizarre signals being received both here and at Goonhilly on the Quick Tune display.

I now cannot send anything from SDR Console via Tune or Tone that is received at Goonhilly.

I brought my Pluto into the house and also the Leo Bodnar GPS set up that locks its LO to 40 MHz instead of an xtal. I don't have a spectrum analyser that goes to 2400 MHz, mine stops at about 1200 MHz. I think.

I do have one of those tiny radio control model power meters and it seemed the Pluto was giving its normal 10 dB when SDR Console was commanded to send a tone or tune signal/ It responded to my SSB voice into the microphone, too.

I put it all back in the box outside and tried the AD preamp direct into the POTY feed co-ax. With my smaller dish I used to be able to have a QSO via SSB to the satellite, albeit not a strong signal, just with the preamp to the POTY. Now I see nothing on Goonhilly...

What I have changed: The dish, the co-ax feeder to the POTY, (McGill Microwave professionally made up LMR-400 and terminated in male SMA's each end by them. POTY is as before and appears undamaged.

The PA is getting power, but I haven't yet measured current draw in TX. The pre amp is getting power.

My suspicions: Not the dish it seems to receive OK. Maybe the brand new co-ax feeder to the POTY is faulty? Maybe the pre amp is kaput? Could I add a 100 dB attenuator and carefully ramp Pluto output up and look at it with my little power meter? Maybe the PA is kaput? Hope not, SG Labs always seem to be behind with orders...

I also have no way I can think of to knowing if the Pluto is outputting a rubbish signal, I reloaded the firmware that's always worked and correct for the PD4. It made no difference. PD4 Pluto menu shows correct IP address, LO frequency, both cores enabled and extended frequency enabled. I have had to reload the boot firmware or whatever it's called before now, but from memory the Pluto was doing sod all and obviously very unwell in order to need that doing. Is there mileage in doing that again?

Here are screenshots of what to me looks like the initial two seconds of OK signal, then one of the less spattery bizarre changes after two seconds. Reducing input power to the Pluto from 0 dBm to -15 resulted in no signal received here or at Goonhilly.

All and any help or advice much appreciated, thanks.

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G8GKQ
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Re: Help please, funny signal from Portsdown 4

Post by G8GKQ » Thu Apr 28, 2022 9:15 pm

Hi

I would suggest testing the Portsdown/Pluto/MiniTiouner combination at 437 MHz 333 kS across the shack (no amplifiers, just 1/4 wave whip aerials).

Then you can troubleshoot and see what is happening usuing your sprectrum analyser. Once you have it working at 437 MHz, go to 2409.75 MHz on the TX and RX and check that, then try re-installing in the QO-100 system.

Dave, G8GKQ

g8lce
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Re: Help please, funny signal from Portsdown 4

Post by g8lce » Fri Apr 29, 2022 8:12 am

I had a strange Pluto problem where it would only connect for a number of seconds. It was normal when looked at via the USB. I cured all by doing a complete reinstall as in viewtopic.php?f=15&t=7862
Not the first time this has worked for me.

Martin G8LCE

g8gtz
Posts: 1733
Joined: Wed Apr 07, 2010 6:26 pm

Re: Help please, funny signal from Portsdown 4

Post by g8gtz » Fri Apr 29, 2022 8:49 am

Yes, sounds familiar.

The general rule with any Pluto problem seems to "If in doubt, do a DFU reset".

Full instructions here: https://wiki.batc.org.uk/Adalm_Pluto#DATV_firmwar

Follow all the instructions exactly as written...

73
Noel

Basil
Posts: 295
Joined: Tue Sep 10, 2013 7:28 pm

Re: Help please, funny signal from Portsdown 4

Post by Basil » Fri Apr 29, 2022 12:34 pm

Thank you Dave, Martin and Noel. I did a DFU reset and it seems to have sorted it for now, after being up until after 2.00 AM fiddling with it. I think I will bite the bullet and buy a spare Pluto as it's probably only a matter of time before something terminal occurs.

May I ask if Digikey and Mouser UK are supplying only the latest versions now, and I can be assured of getting one with the micro co-ax sockets for external reference input? Rev C I think?

I had a late night thought as to whether 8 mA from the Leo Bodnar was enough as I see posts about people using more drive? Could a loss of sensible reference screw the things up?

Where do we go when the Pluto is unavailable, it seems the Lime is still currently unavailable? Do we have "a plan"? :)

Thanks again, and fingers crossed....

G8GKQ
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Re: Help please, funny signal from Portsdown 4

Post by G8GKQ » Sat Apr 30, 2022 7:50 pm

The plan was to continue to support the LimeSDR Mini as the prime SDR solution for the Portsdown. However, we failed to predict the pandemic and the subsequent global chip supply shortage, which prevented the continued manufacture of LimeSDR Mini V1.

The good news is that LimeSDR Mini V2 is now in the late stages of manufacturer's testing prior to volume production. As soon as I can get my hands on one to test, I aim to modify both Portsdown 2020 and Portsdown 4 to support it.

Support for the Pluto is much more complex due to the ever-changing (and non-compatible) hardware versions sold by Analog Devices. The custom ATV firmware needs to be written and maintained by someone else as I do not have that level of expertise.

Dave G8GKQ

Basil
Posts: 295
Joined: Tue Sep 10, 2013 7:28 pm

Re: Help please, funny signal from Portsdown 4

Post by Basil » Sat Apr 30, 2022 9:56 pm

Thanks Dave, it's good to know the Lime is expected to be available again soon. The Pluto has behaved itself for the few occasions I have used it today. I have been playing about with the new dish alignment, and realising how critical large dishes are, as I was warned on here. The margins between good and gone are remarkably tight, and I am glad I went the extra mile in ensuring rigidity of the mounts!

I'm not sure what represents a decent MER on say the wide band beacon, I did fleetingly see 12 something, but lost the setting again. It's very overcast here today, and the 12+ was in a moment of clear skies. What should I be aiming for to assume a pretty sound alignment please?

One annoyance was I used all stainless nuts and bolts and in my haste ordered some M16 set screws and Nylocs off Ebay, as in my job I rarely have cause to use such big (heavy) fasteners. The one that locks the azimuth quadrant was torqued and seemed OK, but it slowly dawned on me the dish was still rotating fractionally when I fiddled with the elevation. I found the thread forms so poor the things were locking up when torqued instead of clamping correctly. I found an Unbrako cap head and Nyloc in 5/8 UNF, which is near as damn it the same size, and sorted that problem. I should never have bought unbranded fasteners off Ebay for anything of importance, especially stainless, which likes to gall at the best of times :)
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G8GKQ
Site Admin
Posts: 2798
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Re: Help please, funny signal from Portsdown 4

Post by G8GKQ » Sun May 01, 2022 11:23 am

Hi

An MER of 11+ on the beacon is good enough. It depends on dish size, but the best that I can get on my 1.2m with a POTY feed (which also makes a difference if not optimised) is 10.2 dB.

Typical Beacon MERs are listed here: https://wiki.batc.org.uk/Receiving_Osca ... he_signals

Dave, G8GKQ

Basil
Posts: 295
Joined: Tue Sep 10, 2013 7:28 pm

Re: Help please, funny signal from Portsdown 4

Post by Basil » Mon May 02, 2022 1:59 pm

Thanks again Dave, there are a couple of mechanical elements of the mount that needed modifying and their implementation was rushed and inelegant, and it's bugging me, so I will remake them, which means another setup session, but every day is a school day as they say, and maybe I can improve reception further.

What I would really like is a portable signal level meter that works on QO-100, as viewing MiniTiouner software on a remote desktop type application on my phone has huge lag and break up. Do such things exist at a reasonable cost, secondhand?

g8gtz
Posts: 1733
Joined: Wed Apr 07, 2010 6:26 pm

Re: Help please, funny signal from Portsdown 4

Post by g8gtz » Mon May 02, 2022 4:17 pm

Have you tried the P'down rxr?

It has full MER and D readout - take a look at the pictures here: viewtopic.php?f=75&t=7846&start=10

If you want an MER readout to adjust your dish on the QO100 beacon, press beacon MER = you won't find a bigger readout anywhere! I'm sure there's a picture of it on the forum somewhere, but I'll leave you to find it!

73
Noel - G8GTZ

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