External LNB power with the MiniTiouner question please?

Discussion about the MiniTiouner board and the MiniTiouner Digital ATV Receive Software. See also http://www.vivadatv.org/index.php
g4eml
Posts: 666
Joined: Thu Apr 26, 2018 9:36 am

Re: External LNB power with the MiniTiouner question please?

Post by g4eml » Sat Apr 24, 2021 8:49 pm

That screen capture shows the LNA Gain is low (with the sad face, at the top of the screen to the left of the Minitioune logo). This is automatically adjusted by the tuner. A normal value is more like that on Colin's screen at around 10dB.

From memory JP added that sad face to indicate that the signal from the LNB was too high and the tuner might be overloaded. In practice it doesn't normally seem to be a problem but it might be worth adding an attenuator between your bias T and the Tuner to see if that improves things.

Colin G4EML

Basil
Posts: 291
Joined: Tue Sep 10, 2013 7:28 pm

Re: External LNB power with the MiniTiouner question please?

Post by Basil » Sun Apr 25, 2021 11:17 am

g0mjw wrote:
Sat Apr 24, 2021 6:07 pm
What is the level of the NB transponder noise floor relative to adjacent clear spectrum below? With a 1.8m dish it should be 9dB or so, but it's possible to lose 10 dB easily with the narrow beamwidth of a large dish such that the SSB signals are still OK but the DATV ones are not.

If you could post a spectrum analyser or SDR plot of the LNB output it would help. In the old days it wasn't reasonable to expect someone to have a spectrum analyser but Lime/Pluto SDRs and the TinySA have really changed that.

Failing a spectrum analyser, the Scan and Tioune software can do something similar using the Minitiouner.

Mike

Hi Mike, thanks for sticking with me, I am afraid i am getting a bit out of my comfort zone and probably am about to attach screen shots which are of little to no use. But what I am thinking is the dish / LNB are not grabbing any DATV signals at all, or they are so weak as to be useless. Before I start moving the mount settings about I will attach these screen shots in case they can confirm or deny my thoughts. I am using an RTL dongle that hears SSB stuff seemingly fine and what Goonhilly sees and hears, I seem to as well. But maybe the big dish is masking poor alignment? SSB via the dongle, 10.915GHz via dongle, 10.48975GHz via dongle and SNR level on SSB on the dongle. Any help? Thanks a lot again Mike.
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Basil
Posts: 291
Joined: Tue Sep 10, 2013 7:28 pm

Re: External LNB power with the MiniTiouner question please?

Post by Basil » Sun Apr 25, 2021 11:23 am

g4eml wrote:
Sat Apr 24, 2021 8:49 pm
That screen capture shows the LNA Gain is low (with the sad face, at the top of the screen to the left of the Minitioune logo). This is automatically adjusted by the tuner. A normal value is more like that on Colin's screen at around 10dB.

From memory JP added that sad face to indicate that the signal from the LNB was too high and the tuner might be overloaded. In practice it doesn't normally seem to be a problem but it might be worth adding an attenuator between your bias T and the Tuner to see if that improves things.

Colin G4EML
Good afternoon Colin, thanks for the reply. I am finding the signal level is giving LNA gain issues if I connect to the LNB WITHOUT an LTE in line filter. With the filter there's no issue and it shows about 13dB gain. With my Pluto I have to use the filter or I see hundreds of lines of spurious signals on the waterfall, equi-spaced. The RTL dongle has no issues with or without the filter, I assume because the band width of its front end is not as wide as that of the Pluto?

I have tried between 10 and 30dB attenuation but I still see no locking, and as in my reply to Mike just now, am suspecting the LNB is not actually furnishing the MiniTioune software with a usable signal.

G8HKN
Posts: 52
Joined: Mon Jan 21, 2019 4:04 pm

Re: External LNB power with the MiniTiouner question please?

Post by G8HKN » Sun Apr 25, 2021 12:12 pm

Basil/Chris
Instead of Beacon have you tried to receive any stations at the other end of the transponder ?
I had a problem with stations in the first 1Ms slot and this was cured by setting the Symbol rate decode to Scan instead of Fixed.
Roger G8HKN.

g4eml
Posts: 666
Joined: Thu Apr 26, 2018 9:36 am

Re: External LNB power with the MiniTiouner question please?

Post by g4eml » Sun Apr 25, 2021 12:45 pm

It does sound like it might be just that the dish is not perfectly aligned. Dish alignment is much more critical on wideband than it is on narrowband. You really do need to tweek the position for every last dB.
The narrowband signals are so strong that a misaligned dish will still work. You can’t get away with that on Wideband.

As has been suggested you should first adjust the dish to maximise the narrowband transponder noise floor.

If you set your SDR to display as wide a spectrum as possible (several MHz) you should see a well defined ‘hump’ which is the noise floor from the narrowband transponder with the narrowband signals sitting on top of it. You need to maximise the amplitude of this ‘hump’.

Colin.

g0mjw
Posts: 2311
Joined: Sat Sep 20, 2014 9:15 am

Re: External LNB power with the MiniTiouner question please?

Post by g0mjw » Sun Apr 25, 2021 1:33 pm

Basil wrote:
Sun Apr 25, 2021 11:17 am


Hi Mike, thanks for sticking with me, I am afraid i am getting a bit out of my comfort zone and probably am about to attach screen shots which are of little to no use. But what I am thinking is the dish / LNB are not grabbing any DATV signals at all, or they are so weak as to be useless. Before I start moving the mount settings about I will attach these screen shots in case they can confirm or deny my thoughts. I am using an RTL dongle that hears SSB stuff seemingly fine and what Goonhilly sees and hears, I seem to as well. But maybe the big dish is masking poor alignment? SSB via the dongle, 10.915GHz via dongle, 10.48975GHz via dongle and SNR level on SSB on the dongle. Any help? Thanks a lot again Mike.
That does look like there is limited SNR. Can you zoom in on the vertical scale a bit? I can't quite read the numbers but would expect at least 8 dB of lift on the transponder. That would explain why you are not seeing the beacon. The problem is the SNR on SSB signals is the made up of the ratio of signal power to the (band nose + transponder noise). In your case transponder noise looks only slightly larger than band noise. It will only drop your SNR by less than 3 dB compared with no band noise at all. The situation with the wideband transponder is different. It has a much lower noise floor so dish misalignment makes a larger difference.

Mike

Basil
Posts: 291
Joined: Tue Sep 10, 2013 7:28 pm

Re: External LNB power with the MiniTiouner question please?

Post by Basil » Sun Apr 25, 2021 2:32 pm

Success at last! It seems the dish alignment was off a bit, and the reason I believe was I just did a wild setting of the polar mount as I didn't want to motorize it. My mistake I believe was as I adjusted the azimuth I was also changing the elevation. Whatever, some careful adjustment and much running in and out has succeeded in getting the beacon to decode.

I do have a nice spectrum analyser, an HP 8568B but I am not very good with it and live in fear of doing something daft and blowing the front end up. But the other reason is it weighs a huge amount, is elderly and like me probably wouldn't take kindly to shocks and bangs. It's in my workshop and the stuff for decoding is my truck near the satellite dish until I could prove running cables to the shack was worthwhile.

Sincere thanks to all who helped.

I am left with a couple of questions. What is the relevance of having 32 bit VNC loaded and establishing some sort of network link to it please? I have it on the laptop, but no network link to it, I admit I have no idea of why there might need to be one...

Secondly is there something available better than a cheap Ebay satellite finder meter, but more portable than my lovely old HP 8568B for aligning dishes in the field?

Hopefully I can progress to receiving narrow band DATV next, thanks again everyone.
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g0mjw
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Joined: Sat Sep 20, 2014 9:15 am

Re: External LNB power with the MiniTiouner question please?

Post by g0mjw » Sun Apr 25, 2021 2:38 pm

The Ryde with Minitiouner or Portsdown with Minitiouer has a beacon MER setup that will display the MER in very large numbers you can see from the garden. It can also beep suitable if that helps. Great for fine tuning.

Mike

Basil
Posts: 291
Joined: Tue Sep 10, 2013 7:28 pm

Re: External LNB power with the MiniTiouner question please?

Post by Basil » Sun Apr 25, 2021 4:08 pm

That sounds good, I am part way through assembling a Portsdown, the touch screen arrived on Friday, so I will have a go at this. I have decoded some other wide band signals now, but the MER figure is poor and the decode drops in and out. I would have thought a 1.8 meter dish would be good, should I still consider the alignment? It's on a 4 inch OD steel tube in concrete, but if you pull and push the dish there's some flex as I wanted to keep it high enough off the ground to be dog proof from very big dogs, and to ease garden maintenance. I am beginning to wonder if today's wind is a factor...? Thanks Mike, and for more good news, Jean-Pierre got back to me today and I can access the Viva DATV forum again now :) I have downloaded the scanandtioune package for a look see.

g0mjw
Posts: 2311
Joined: Sat Sep 20, 2014 9:15 am

Re: External LNB power with the MiniTiouner question please?

Post by g0mjw » Sun Apr 25, 2021 7:29 pm

You are a couple of dB down. Check the focus.

Mike

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