Erratic failed recordings

@TabloEngineering @TabloSupport @TabloTV

I have a Gen 4 Tablo set to record a daily program from an OTA channel. The Channel list that results from a scan shows this channel as 1080i and shows 4 green dots, suggesting it is a pretty strong signal.

However, on 2 or 3 of the recordings from the past week, when watching the recorded show the playback becomes pixelated, audio breaks up, then recovers. This repeats several times, finally crashing to a blue screen with a notice of “… failure to decode… blah,blah,blah.” Also includes a “helpful” note that this is likely due to a weak signal, despite the signal indications I noted above.

If I hit the retry button and very quickly fast forward, I can sometimes get past the “glitch point” and continue playback, sometimes without error, other times with the smae sequence of errors eventually repeating.

I have checked all connections, all appear solid. I have done rescans and get teh same signal strength indications.

Configuration: Tablo Gen 4, Ext 2TB Samsung SSD, Ethernet connection to wifi6 mesh access node. playback on FireTV Cube app.

Every time I start up playback, I never seem to know what I’m going to get. Anyone else see similar issue? Any suggestions?

signal strength is not an indicator of signal quality. sometimes adjusting the antenna a few degrees will help the signal quality

OK, thanks. I guess I’m a bit confused.

I thought in the age of digital signal transmission, the signal was either there or not. Strength might wane with distance or obstacles (tree limbs, etc.), but if strong enough to be received, then digital quality should be good.

My antenna is affixed to the inside of an upstairs window pane, the only window in the house that faces the general direction of the local broadcast towers. With that orientation, I am receiving 50+ OTA channels all with 4 green dots for signal.

How do I go about determining or measuring “signal quality?”

Signals are affected by type of reception(line of sight, multi-path, the right antenna/amplification and interference, etc). I could have a low signal strength of 57 but a good S/N of 22dB+ and thing will work fine. My OTA will also work down to a dB of 18 if the signal strength is high. hi-vhf channels have range limitation and usually require an antenna that supports hi-vhf.

I know the actual compass location of my OTA towers and adjusted the antenna in such a way. tablo doesn’t expose a signal meter so I verified everything using a TV which had a built in meter. Many urban users that don’t have interference don’t need to go to all that trouble…

A TV receiver will typically have a minimum S/N of 30 dB, some claim as low as or lower than 20 dB. In real world conditions interference from signal multi-path, other transmissions, and nearby electronic sources, effectively increases minimum S/N to 30 dB.

First, how far away from the towers are you?
Do you have an amplifier on your antenna?
If you don’t and you live pretty far from the towers maybe it would help.
If you do, try turning it off if it is on and vice versa. Sometimes amplifying will result in over-saturation causing similar symptoms as not having a strong enough signal.

I use a clearstream 2v and channel master 3414 - for legacy tablos. The antenna is attic mounted. I have line of sight to 4 UHF towers at 22 miles, one UHF tower at 31 miles, and 2 hi-VHF towers at 13 miles. All full power stations. The spread between the towers is 86 degrees.

The gen 4 is using the build in amplifier, and first story window mounted sky antenna not optimally pointed. The gen 4 can still receive all but the 32 mile tower

It’s a gen 4 turn off the amplification if over amplfied. I original poster reported 4 green bars not 5 green bars.

Should also mention that atmospheric conditions can affect reception, especially if other stations further away but in line with your antenna are on the same frequency. The repack made it much worse. I can have a station with a strong signal and good SNR, but an hour later, the SNR will tank, even though strength is the same.

What’s good S/N - 27dB and above. And how far does it tank 19dB and below. I normally don’t have really crappy weather and it doesn’t decrease over 5-6 dB during a storm. Of course when the neighbors turn on their equipment and try to contact their home planet reception is bad.

It’s not always obvious. You can have two evenings or nights with what seems like identical ground weather, but high atmospheric conditions may vary. It may sometimes allow signals to bounce or duct much further than the typical straight line signals.

My farthest local tv tower is 22 miles. And after that it’s 110 miles miles to the next set of towers. So maybe I’m lucky to not have tropospheric conditions. We had a tropical storm roll through for a few days in august and there was no impact on reception.

@zippy Yes, I am using a Gen 4. the antenna is amplified and I also turned on amplification within the TabloTV android app. Before doing so, I only scanned about half the stations I now have in the scan. Are you suggesting my channel of choice (62.1 locally, Kansas City area) might be “over-amplified” and this could cause the recording glitches I see?

I am something like 17-20 miles from the transmitter. My antenna is inside a clear window pane that is within 10-15 degrees (maybe less) of the tower. Relatively open suburban area with no obvious building obstructions.

@andyross The show I have scheduled to record is a 10 - 11 am show time, so nighttime atmospheric layers should not be generating longer distance interference. My antenna location is about 25 feet above ground level, so I should have pretty much line of sight.

Thanks to you all for some interesting discussion. Next recording will be Monday am and will attempt to play back Monday evening. Please keep the suggestions coming. Cheers.

Someone else suggested over amplification.

One thing you can try is the allocation map on If you know the RF channel your problem station is on, you can put that in and see what stations around the country are on that frequency. You can zoom in and look to see what nearby stations may be in line with your antenna. If you don’t know the RF channel it uses, you can see it on the rabbitears report or just post the call letters here and somebody can let you know.

@andyross Thanks. I went there and entered the RF channel of my problem station (32). If I understand teh resulting map, there is another transmitter nearby on RF 31 and another on RF 33. All three appear to be full power transmitters. My location is within the Blue circle surrounding those transmitters, but I honestly don’t know what that means.

I did check for any other co-channels within 100 miles. There is one station in the opposite direction from my problem channel that also operates on RF 32, but is a low-power station and my location does not fall within the forecasted reception area of that station (at least according to his map – they reception areas do not overlap.)

But, I feel a little like a pig looking at a wristwatch – this is all shiny and interesting, but what is it? Does this really mean anything to me? Just not familiar enough with RF propagation theary and digital transmission characteristics. (Oh, and my channel scan is not picking up anything in the general direction of the distant low-power co-channel.)

Another interesting site to see predictions of ducting and similar can be found here. Someone on another site posted a picture from there of the Chicago and upper-midwest from yesterday. I think one reason I have so many issues is that Lake Michigan may also play a part in it, and my, and many Chicago area residents, have their antennas pointed that way and get interference from Michigan stations.

Maybe if users use an antenna where the local channels are all 5 green dots ducting wouldn’t be a problem. And things must be good today in chicago. Nothing coming from Michigan.

About 120 miles north of Chicago I have 2 Televes long range mix antennas on my roof precisely aimed north and south to the cluster of towers in those directions about 45 to 50 miles away. The only amplification I use is what’s built into the antennas. All my channels in Tablo have 5 green dots currently. I only rescan Tablo when I know conditions are favorable. But there are days where certain (predictable)(and sometimes unpredictable) channels are weak or completely gone. It always seems to be the nicest days and even nights. Clear, warm and on the humid side. Oh yeah and the repack didn’t help any. I always look forward to late fall and winter when reception is rarely an issue.

Update to all:

As promised, I did a rescan over the weekend. The scheduled channel/program recorded on Monday am; we played it back on Monday evening and it played flawlessly. No changes in settings anywhere in the system/infrastructure. Only “change” was to do a fresh rescan the night before.

Did NOT do rescan last night, so we will see how the quality turns out in tonight’s playback.

Thanks to all. Cheers.

1 Like

Another Update:

We had five days of recording this same show on the same channel this past week. Each evening, we played back that day’s recorded show. Results:

Mon - Thur: All playback was perfect. Superb video, no audio lag, no pixelation.

Fri: Pixelation was back on this recording. Several cases of 1-2 sec jumps in video/audio, and two instances of the BlueScreen “Failure to Decode” issue. I was able to hit the Retry button and immediately fast forward to a point 10-20 seconds past the failure point, then proceed with playback.

Will do another channel rescan this weekend to try to maximize signal and see what we get next week.

@TabloSupport @TabloEngineering @TabloTV

There are issues with LTE and 5G celphone towers interfering with tv reception. I got a filter as suggested in the video. To make matters worse,T Mobile and others are now putting 5G internet gateways in the home. You could easily have a 5G transmitter in the house next door. They transmit on very low power so should not interfere much.