SOLVED: Quad HDHR single tuner freezing.

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PhilB
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Posts: 403
Joined: Sun May 11, 2014 6:23 pm
Great Britain

Re: Quad HDHR single tuner freezing.

Post by PhilB »

This is proving to be an interesting problem and I think it’s time to give a recap and an update on this long running thread.

Setup
Running xubuntu 20.04 / Mythtv v32 /Silicon Dust Connect Quattro / directional loft aerial with lots of elements/ DVBT from Crystal Palace London transmitter.

Problems
Problem 1: Occasional failed recordings; no file created.
Problem 2: A lockup of a tuner. A backend restart or system reboot will not clear this, but a tuner reboot or power cycle does. The fault is infrequent – an EIT scan will fail with: 'ERROR: lock no longer held' after which further EIT scans fail and all recordings from a first multiplex fail. Those scheduled at the same time from a second multiplex – and hence a different tuner - work. Failures seems to happen much more frequently in fine weather.

What’s unique?
The Quattro and Mythtv is a popular and well respected combination and nobody else has reported similar problems, so what might be unique about my setup? Two things I can think of:

1. Crystal Palace transmitter has two multiplexes which are offset from nominal frequency by -166KHz. See the ‘-‘ indications for channels 28 and 30 on this page: https://ukfree.tv/transmitters/tv/Crystal_Palace
2. We live near Heathrow and aircraft could be a factor.

Things Tried
Setting first tuner for active EIT scanning but putting it low priority for recordings to avoid EIT/recording switching.
Network traffic testing from backend to tuner.
Using a dedicated gigabit switch for tuner and backend.
I read that a very strong signal can lock the tuner so I attenuated the aerial signal by 12dB - it now has a signal strength 82% but quality 100%.
Increasing buffering.
Spinning recording disk up before start of recording.
Hiding all channels and disabling EIT on the multiplexes with the offsets (but I think it did the scanning anyway)
Increasing tuning timeouts (needed especially for DVB-T2 channel scanning).
An override file to reboot the tuners on backend start.
A cron job to check logs and restart backend (and reboot tuners) if necessary. This restored some stability but is a nasty kludge.

Provoking Failures
At Klass's suggestion I wrote a perl script to use the API and trigger lots of manual recordings on a backend. See:
https://www.mythtv.org/wiki/Swamp_backe ... recordings

I found that alternating recordings between two particular multiplexes with one minute recordings (plus pre/post roll) and one minute gaps readily induced failures –
- Com6 with a nominal frequency of 530MHz but ‘offset’ by -166KHz and
- Com5 with a frequency of 482MHz.

In particular, switching between ‘Yesterday’ on Com6 and ‘Film 4 +1’ on Com5 would result in most of the ‘Film 4 +1’ recordings failing, but they did not freeze the tuner. If you receive Crystal Palace you might like to try this!

This was also repeatable with v34 master when I loaded on an old laptop and Klaas kindly put in a lot of work and provided fixes:

See:
https://github.com/MythTV/mythtv/commit ... dd889b104b
and
https://github.com/MythTV/mythtv/commit ... 26778dd22b

With these fixes in place I could no longer break it with v34 even with hundreds of recordings. Fortunately, by that stage I had included code to remove all the test recordings!

What Next?
I installed xubuntu 22.04/Mythtv v34 on our main system last week and am optimistic the Klass’s fixes will be effective in fixing both the random recording failures and the lockups.

I am still a little suspicious of the Heathrow connection but the sole and rather flimsy evidence for this is a possible increase in frequency of lockups in fine weather when planes are scheduled to overfly us and the signal path. Silicon Dust support suggests that transmissions from the aircraft (113~131MHz) are unlikely to be an issue but do think that multipath interference bouncing off the undersides of planes is a possible factor. DVBT is claimed to be resistant to multipath but perhaps not to fluttering multipath. They suggested tilting the aerial downward to avoid this.
I want to do this one step at a time to really nail the problem so will leave it as it is. If it recurs then I’ll look at filtering (a TV/FM diplexer should work) and aerial tilting.

Comments?
I’d appreciate ANY comments, views etc on the above.

Thanks
My thanks to Klaas for his unstinting support during this process; also to Bill for testing swamp with US data.

Phil
blm-ubunet
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Posts: 265
Joined: Sun Jun 15, 2014 1:08 am
Cambodia

Re: Quad HDHR single tuner freezing.

Post by blm-ubunet »

DVB-T(2) uses CODFM & thousands of carriers in band.
This means the symbol rate on a carrier is very low & multipath typically can not cause problem.
It was designed with multipath & urban canyons in mind. DAB radio etc.

The best* antenna for DVB-T is ganged array flat panel & not a yagi style with loads of elements & highly directional.
The ganged array (almost phased array) can achieve similar effective gain as yagi but without the directional problem so it can solve fluctuations caused by reflections off metal roofs, wet trees blowing in wind & aircraft.

* And these antenna are cheap & less obvious on side of a house/chimney.

The local TV antenna people should know if you need a tuned notch filter. The best & cheapest is a length of coax cable tuned to the problem frequency. I thought broadcast FM radio was typically the problem.

There were stories floating around that the first cars with ECUs cut out when driven past airfield radar. No sure I believe that but I seen some really bad electronics in cars.
PhilB
Senior
Posts: 403
Joined: Sun May 11, 2014 6:23 pm
Great Britain

Re: Quad HDHR single tuner freezing.

Post by PhilB »

Thanks for your reply.
If it turns out that Klaas's fix has not resolved the problems than I'll be looking further into antenna and filter issues. I can't find any info on ganged array flat panels or your coax filter. Are you able to suggest some urls for those please?

Phil.
blm-ubunet
Senior
Posts: 265
Joined: Sun Jun 15, 2014 1:08 am
Cambodia

Re: Quad HDHR single tuner freezing.

Post by blm-ubunet »

Those antenna get called phased arrays but I don't think that is true description.
https://www.jaycar.co.nz/heavy-duty-uhf ... a/p/LT3154

Coax filter is a 1/4 wave stub.
Online calc here:
https://www.arcticpeak.com/antennapages ... vestub.htm
It is possible some strong local intermittent signal upsets the tuner's radio frontend AGC or AFC.
But your local TV signals are very strong.
Consumer electronics are made to a price but some of these cheap TV tuners make excellent SDRs & the local oscillator/clock is the weakness.

This site is cool for checking line of sight etc.
http://www.heywhatsthat.com/profiler.html
PhilB
Senior
Posts: 403
Joined: Sun May 11, 2014 6:23 pm
Great Britain

Re: Quad HDHR single tuner freezing.

Post by PhilB »

Thanks for that useful information - I didn't know they were called stubs.

Enquiries with BBC also suggested aerial tilting but their response also mentioned phone signals - almost as an aside. This is something I stupidly had not until then even considered. There is a mast only 200 metres away directly behind and in line with the aerial ! It would only need about 16W to compete with Crystal Palace is 20Km away with 200KW per multiplex and I'm sure they pump out lots more than that.

I have contacted https://restoretv.uk/ - they think it a possibility and have sent me a filter. Postings in the Silicondust forum also mention phone mast interference. Too early for predictions but fingers crossed.

Phil
PhilB
Senior
Posts: 403
Joined: Sun May 11, 2014 6:23 pm
Great Britain

Re: Quad HDHR single tuner freezing.

Post by PhilB »

Well, the 4G/5G phone filter made no difference. Tilting the aerial down by a massive 20 degrees to reduce the likelihood of multipath reflections from aircraft did not either - I had 7029 errors, failed recordings and the tuner locking up even when aircraft were taking off the other way.
In desperation because I cannot now think of anything else I suggested to Silicon Dust that there was a hardware fault and would they do a warranty exchange - they replied:
"The symptoms suggest a hardware issue with your HDHomeRun. We will replace it."
I'm just still within the 2 year warranty. Item posted today.

A breakthrough??

Many thanks for the continued support, suggestions and encouragement from this community.
Phil
PhilB
Senior
Posts: 403
Joined: Sun May 11, 2014 6:23 pm
Great Britain

Re: Quad HDHR single tuner freezing.

Post by PhilB »

Following replacement of the connect tuner I'm finding things a lot more stable. I no longer get the 7029 errors but I have had two unprovoked instances of the 'lock no longer held' messages in 4 weeks. One of these was benign but I'm not sure about the other one because my automatic restart mechanism tripped in coincidentally about a minute later.
I have a report of 7029 errors with another backend installation.

I'm launching a survey under a new thread to see if others hit this problem.
Thanks for all your support with this problem.
Phil
PhilB
Senior
Posts: 403
Joined: Sun May 11, 2014 6:23 pm
Great Britain

Re: Quad HDHR single tuner freezing.

Post by PhilB »

I am finally marking this as solved. Since changing the tuner on 24 June 2023 I have only had two instances of 'lock no longer held'. They are associated with EIT scanning and appear to be benign. No instances of 'Error 7029' and no tuner lockups.
Thanks all for your assistance and considerable support with this.
Phil
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