Order of chaining T4 tuners

[Altimes]

Had a somewhat broken up recording last night that caused me to look at signal strengths and wonder if I need to reseat the antenna cables.

Created a contrived context in which I could access each tuner. A,B,C,D showed signal strength of something like 67%, 72%, 75%, 100%. With the recording in question having a Tuner-A tag. OK, the smart among you have already worked out that I have (unconsciously) daisy chained the tuners from right to left (from the back of the T4), that is antenna->D->C->B->A->TV. I have now set tuner D as the the preferred tuner for recordings.

The 25% loss on the first link looks suspect, so I will wrestle the box out of the cabinet and reseat that link.

To me, working in from the edge inward just seemed the "sensible" wiring, I am curious to know if I am alone in reverse hooking up the signal feeds and if there are any consequences of having done so ? (apart from needing to set a preferred recording tuner to get the strongest signal)

Regards,

Alan

[IanSav]

Hi Alan,

I am no expert in this area but it seems to me that you would want to correctly maintain the order of the tuners in case there is any amplification of the signal across the tuner set.

EDIT: To clarify, as MrQuade better explained, when I said the correct order I meant connecting the antenna to the IN of a tuner and that tuners OUT to the IN of the next tuner, etc.

Regards,
Ian.

[MrQuade]

Created a contrived context in which I could access each tuner. A,B,C,D showed signal strength of something like 67%, 72%, 75%, 100%. With the recording in question having a Tuner-A tag. OK, the smart among you have already worked out that I have (unconsciously) daisy chained the tuners from right to left (from the back of the T4), that is antenna->D->C->B->A->TV. I have now set tuner D as the the preferred tuner for recordings.

Why did you need a contrived context to test the strength of each tuner? If you want to test each tuner, all you need to do is set the preferred tuner for live TV to one of the tuners, and then change channel to apply the change.

Also note that when you are testing signal strength, you really need to be using the same channel for each test since each broadcaster will potentially be at a different level. I am unsure from your description if you were able to get a signal strength reading all from a single broadcaster,


The other thing I am curious about is you should have been getting a *stronger* signal from the tuners further down the daisy chain. Each tuner has its own signal amplifier in it, and in most Wiz units, they actually boost the signal to a level that is slightly above the signal that came in. This is not necessarily a *good* thin mind you, but that is how they generally behave.

To me, working in from the edge inward just seemed the "sensible" wiring, I am curious to know if I am alone in reverse hooking up the signal feeds and if there are any consequences of having done so ? (apart from needing to set a preferred recording tuner to get the strongest signal)

As long as you connected the antenna to the tuner's "IN" port and then daisy chained from the OUT port to the next IN port, it shouldn't matter which order the tuners are connected.

Just check the labels and connect to IN, then OUT to IN, OUT to IN etc... Your preference as to which order to do that in, but A to D would be more normal.

[Altimes]

Why did you need a contrived context to test the strength of each tuner? If you want to test each tuner, all you need to do is set the preferred tuner for live TV to one of the tuners, and then change channel to apply the change.

Lazy. Seemed easier to trigger an instant recording off of 4 discrete broadcasters to ensure that I could examine each tuner.

Also note that when you are testing signal strength, you really need to be using the same channel for each test since each broadcaster will potentially be at a different level. I am unsure from your description if you were able to get a signal strength reading all from a single broadcaster,

I had not considered that aspect. However, I receive signal for all broadcasters from the North Head repeater in Sydney. As such I suspect that they are all at the same strength.

The other thing I am curious about is you should have been getting a *stronger* signal from the tuners further down the daisy chain. Each tuner has its own signal amplifier in it, and in most Wiz units, they actually boost the signal to a level that is slightly above the signal that came in. This is not necessarily a *good* thin mind you, but that is how they generally behave.

Now I am puzzled. Time, methinks, to reconfigure the antenna feeds.

Just check the labels and connect to IN, then OUT to IN, OUT to IN etc... Your preference as to which order to do that in, but A to D would be more normal.

All good on that front, I just never looked a the alphabetic labels The T4 has been running happily since in was installed, it would have only been disturbed with the need to replace the dead TV recently.

This is the first time that I have encountered any significant signal breakup on any recordings. It is the unusual that causes us to poke into the corners.

The signal feed comes off of a powered splitter which has been quietly doing its thing, untouched, in the garage for the last 12 years, so I probably need to check on it as well. Sadly, nothing lasts forever and after 12 years @ 365 days it might be time to chase the spiders, etc out....

Alan.

[prl]

As long as you connected the antenna to the tuner's "IN" port and then daisy chained from the OUT port to the next IN port, it shouldn't matter which order the tuners are connected.

+1

I recently needed to check the signal levels on ABC on our T4. It had signal strength100% on all tuners. Losing 25% on the D->C loopthrough seems odd.

If re-seating the loopthrough connectors doesn't help, try swapping the D->C cable with one further down the chain (e.g. B->A). Does that move where the 25% signal loss happens? If so, it looks like a dodgy loopthrough cable.

[Altimes]

If re-seating the loopthrough connectors doesn't help, try swapping the D->C cable with one further down the chain (e.g. B->A). Does that move where the 25% signal loss happens? If so, it looks like a dodgy loopthrough cable.

Thanks for that tip. Once I get it out I will try that test.

Alan.

[prl]

However, I receive signal for all broadcasters from the North Head repeater in Sydney. As such I suspect that they are all at the same strength.

While it's true that the North Head transmitters are all the same power (1kW), they don't necessarily all have the same propagation characteristics, even though they're pretty well bunched together with centre frequencies 529.5 - 564.5 MHz.

It's worth checking all the frequencies anyway just to make sure that there isn't something odd going on that has a frequency dependency.

[MrQuade]

All good on that front, I just never looked a the alphabetic labels The T4 has been running happily since in was installed, it would have only been disturbed with the need to replace the dead TV recently.

Just so long as you didn't connect A's OUT to B's IN, and B's OUT to C's IN (etc), but then connected the antenna to D's OUT . I'm not even sure what would happen if you did that......probably nothing good

[prl]

Just so long as you didn't connect A's OUT to B's IN, and B's OUT to C's IN (etc), but then connected the antenna to D's OUT . I'm not even sure what would happen if you did that......probably nothing good

The antenna would broadcast whatever is coming out of D OUT (provided it's within the antenna's bandwidth). Unless the signal being received on the antenna is so large that it damages the buffer amplifier in tuner D, I don't think anything really bad would happen, beyond doing a little unlicensed broadcasting in a licenced broadcast band

[Altimes]

OK. A little more "systematic" testing shows reality somewhat different from casual perception.

I set the preferred tuner and evaluated the signal strength for each broadcaster with the results, in frequency order, below;

Tuner A
66 % - ch 28 (seven)
71 % - ch 30 (abc)
71 % - ch 31 (ten)
69 % - ch 32 (sbs)
73 % - ch 33 (nine)
Tuner B
72 % - ch 28 (seven)
78 % - ch 30 (abc)
76 % - ch 31 (ten)
73 % - ch 32 (sbs)
68 % - ch 33 (nine)
Tuner C
64 % - ch 28 (seven)
68 % - ch 30 (abc)
67 % - ch 31 (ten)
65 % - ch 32 (sbs)
62 % - ch 33 (nine)
Tuner D
71 % - ch 28 (seven)
73 % - ch 30 (abc)
72 % - ch 31 (ten)
71 % - ch 32 (sbs)
66 % - ch 33 (nine)

Sometimes the signal strength to would jump up to 100% for a few seconds and then drop back.

Basically sod all difference between tuners. At the observational level only the ABC was suffering from picture breakup.

Doing a similar (less systematic) check on the U4 (fed on a different run from the same splitter) shows a signal strength of ~91% across the 3 internal tuners.

When I pulled the T4 out and looked *carefully* I had configured it in expected ABCD order Equally I had forgotten that I have a P2 in the signal chain as well. So it probably goes Antenna -> P2-A->P2-B -> T4-A->T4-B->T4-C->T4-D -> TV .....

I think that I need to get back into the rats nest behind the AV cabinet and sort a few thing out (like pensioning off the P2 and feeding the T4 directly from the splitter ).

Alan

[MrQuade]

Sometimes the signal strength to would jump up to 100% for a few seconds and then drop back.

Basically sod all difference between tuners. At the observational level only the ABC was suffering from picture breakup.

Doing a similar (less systematic) check on the U4 (fed on a different run from the same splitter) shows a signal strength of ~91% across the 3 internal tuners.

A 7% swing in the measured strength seems to suggest there is a hardware issue in the signal path to the T4. This is given that you aren't seeing it on the U4, otherwise I would be looking at an antenna issue, or a tower line of sight problem.

Bypassing the P2 is a good start. You could also try a different port on the powered splitter if that is possible in your setup.
Swapping to good quality stiff antenna leads might also be in order if you have any cruddy old spaghetti leads in the mix too.

[peteru]

A 7% delta in those measurements is within the error of measurement. Don't forget that these are instantaneous readings based on the AGC gain of each tuner. Manufacturing tolerances, reception conditions, wiring, external noise, heat and a whole lot of other factors will cause such variations. I'd say that readings within +/- 10% should be expected.

If you have one tuner reading 20% and another reading 95%, then you have a reasonable cause to suspect a tuner / loop problem. Readings of 64% and 72% are close enough and indicate that the problem is somewhere upstream. You need to improve the signal before it's connected to the T4.

[Paul_oz53]

A 7% delta in those measurements is within the error of measurement. Don't forget that these are instantaneous readings based on the AGC gain of each tuner. Manufacturing tolerances, reception conditions, wiring, external noise, heat and a whole lot of other factors will cause such variations. I'd say that readings within +/- 10% should be expected.

If you have one tuner reading 20% and another reading 95%, then you have a reasonable cause to suspect a tuner / loop problem. Readings of 64% and 72% are close enough and indicate that the problem is somewhere upstream. You need to improve the signal before it's connected to the T4.

Reception can vary by frequency, even with small differences in centre frequency as prl and peteru both note. As a young engineer I studied and worked on aerial design for aircraft navigation systems.

If reception is an issue that wasn't present earlier, it suggests damage to the aerial or feed-in cable or cable connection. Spent the last couple of days troubleshooting and replacing my neighbours aerial for precisely that reason. His was 20 years old, corroded and pointing way off line-of-sight but he claims it worked fine until a few weeks ago. But in his case, his reception on ch 7 was buggered while other stations were fine.

New aerial and lead-in and pointed in the right direction has fixed his problem. Strong wind can cause an antenna to spin out of alignment so that may be factor to check, even if the aerial is sound and the lead-in not compromised.

[Altimes]

Thanks for all the input.

Progressively checking the aerial feed line is the tomorrow job on the to do list.

I have also provided local tech support to my parents setup not so long ago. Repeated complaints of unwatchable Channel 7 in Gosford, NSW. It is also one of those locations where multiple signals are available. AutoTune giving rise to 70+ channels Eventually becoming suspicious of an inline Video Recorder not behaving itself I hooked the TV to the wall socket with a spare aerial cable of mine and the problem instantly vanished. The bottom line is that it was a dud cable from the wall socket to the video recorder. It, of course, was the most difficult cable to replace deep behind a very full, very heavy, very large AV cabinet, so it was the one that everyone left in place Once replaced smiles all round.

Similarly recently setting up the U4, grabbed spare new antenna cable which had been sitting around in its packaging for some years. It turned out to be a dud. Sad that QA cannot ensure we can buy reliable cables