menuMENU    UK Free TV logo Archive (2002-)



Click to see updates

All posts by Watt

Below are all of Watt's postings, with the most recent are at the bottom of the page.

I have a strange problem! I'm on the edge of the Sutton Coldfield coverage area (CV35) but have what seems to be a perfectly good signal from a Group B aerial on the chimney and a distribution amplifier.
One of the amp outputs feeds a Humax HDR-FOX-T2 PRV with a Philips flat screen HD-Ready TV daisy chained off it.
For the last 4 months or so, I have been getting picture freezes and breakups while watching the TV via the Humax (connected by HDMI) and when recording stuff on the Humax. This can affect all channels but is mainly on channels from the COM5 and COM6 muxes. When this happens, the Humax reports an adequate signal strength, but dire signal quality. However, if I switch to the TV's tuner and watch the same channels on that, the picture is perfectly ok - and the Philips reports that the qulaity is "excellent"!
I assumed that this must indicate a problem with the Humax. However, I've just had that replaced and the problem is still there - worse if anything!
Where do I go from here?

link to this comment

Yes, both the TV and the Humax are manually tuned to SC's 6 muxes, so it's a like for like comparison. The worst problems are with the COM6 mux (UHF channel 39+, 618.2 MHz on both). There are also problems on COM5 (Ch 45, 666MHz) but the ones in between are largely ok. [I first did an auto tune with no aerial connected, to clear out any spurious stuff, so neither has any 'duplicates' in the 800's.]

I've been trying to think whether I could have done anything to cause the problem. Not long before I started having problems, I installed a power-line ethernet link to connect the Humax to my broadband router. I wondered whether that could be injecting noise into the Humax and affecting that but not the TV. But I've now totally disconnected that, and the problem hasn't gone away! I don't know what to try next.

link to this comment

Many thanks for your suggestions jb38. I'll try them in the daytime tomorrow - which is when the problem tends to occur. It's usually ok at this time (~10pm)of night.
Lark Stoke is in an almost diametrically opposite direction to Sutton Coldfield, and is vertically polarised. Having said that, when I first retuned my TV following DSO (before I bought the Humax) I did pick up some watchable Lark Stoke transmissions off the back of the aerial! I then took to manual tuning, and have always tuned the Humax manually. I surely shouldn't be getting interference from Lark Stoke? It doesn't use any of the same channels as Sutton Coldfield. My most problematic mux is COM6 (39+) and Lark Stoke's nearest to that is its COM4 (41+).

About 25% of my neighbours have their aerials pointing at LS, the rest at SC. In extremis, I could replace the aerial and use LS instead. It might be a better bet in some ways because, although it isn't as powerful as SC, there are less hills in the way. [We're in the shadow of Hatton Hill, with a straight line from SC to my aerial barely clearing the ground in some places]. But that begs the question as to why the Philips TV copes ok but the Humax doesn't! [It's a fairly old (by TV standards) Philips TV - circa 2006. Don't know whether that's good or bad as far as tuner quality goes!]

link to this comment

Antenna power is definitely OFF, and always has been. There is not a lot of co-ax behind the TV. There is a single cable all the way from the distribution amp, which is chased into the wall and emerges from an outlet with its innards removed, and goes straight to the Humax with no intermediate socket or fly-lead.

I have removed the RF lead between Humax and TV with no effect on the signal quality bar. Ditto with waggling the HDMI lead.
The TV (with its own stand) sits on a 3-shelf TV unit, with the bottom shelf about 3" from the floor and the other shelves about 9" apart. The Humax has always sat immediatly on top of a DVD player on the middle shelf, so as to be about 12" under the TV. The DVD player is invariably OFF when not in use - although I suppose by that, I mean that it's on standby, and is receiving SOME power, because it can be woken up by its remore control.

Anyway, in case this is having any effect, I've now moved the Humax - on its own - onto the bottom shelf, so that there is now about 20" of clearance from the bottom of the TV. That MAY have made a BIT of difference - but certainly hasn't effected a total cure. The quality bar on Ch39 is still 'tromboning' but only seems to be going between 100% and about 70% rather than down to 50% or lower before. But it would take a longer period of observation to be sure, because the problem tends to come and go. There is still SOME evidence of picture break-up.

link to this comment

jb38: Based on further observation, I would say that my previous report of some improvement was somewhat premature and that, in reality, moving the Humax further away from the TV hasn't made any difference.

The TV is an 37" LCD model which we bought new in about 2006 - but I have a feeling that it was probably a discontinued model at the time. [I'm not sure that plasma TVs were avaialable at the time].

I understand what you're saying about the respective built-in quality reporting mechanisms. But, aside from that, the proof of the pudding is in the eating! The Humax's picture breaks up, the TV's doesn't.

I also realise that having the signal skimming along the ground doesn't help. [Prior to DSO, digital TV was very unreliable, so I didn't buy a PVR until after DSO]. But that still begs the question as to why the TV is ok but the Humax isn't.

I also find it slightly odd that the two muxes which play up are not at the extremes of the frequency range. Well, actually, COM6 on 39+ is the lowest of the 6 muxes, but well within the range of a Group B aerial, (and Channel 5 analog used to work per4fectly well on Ch 37). COM5 on 45 is flanked by PSB1 on 43 and PSB2 on 46 - both of which are ok.

That makes me wonder whether there's something inherently inferior about the signal quality on the COM muxes relative to the PSBs.

link to this comment

jb38: Many thanks for your continued interest. The TV is a Philips 37PFL5522D/05

Looking at Lark Stoke vs Sutton Coldfield, I'm loath to move to LS because - according to my calculations - the signal strength which I'm likely to receive (1,260 watts at 23.3 kM vs 200kW at 38.4 kM) would be lower by a factor of 60! Also, we seem to be line for some additional HD muxes from SC in a year or two, but I'm not sure when - if ever - LS will carry those.

I suppose that I could hedge my bets by investing in a Group K aerial, which should work for either.

Ian: I've just tried what you suggested. When I plug the downlead directly into the TV, the picture is fine and it reports "excellent" quality on the same channels which are poor, with picture breakup, on the Humax.

I would have been surprised if the Humax provided a better signal to the TV than it used for its own purposes - added to which, "quality" implies signal to noise ratio rather than just signal level. It looks to me as if the Humax is seeing some noise which the TV isn't seeing!

The distribution amp is a Wickes CM7297 (probably made by Labgear) which I've had since Adam was a lad. It claims to have a gain of 6dB on each of its 6 outlet ports.

link to this comment

jb38: Thanks for your further input.
I'm not sure I totally understand your first question, but here goes. When I'm viewing TV using the TV's own tuner, the picture is perfectly ok regardless of whether the downlead is plugged directly into the TV or looped via the Humax. It's only when viewing (or recording) using the Humax's tuners that breakup occurs. Removing the RF lead between Humax and TV makes no difference to this.

Power saving on standby is definitely turned off. But, in any case, that would only affect trying to use the TV's own tuner with the Humax on standby - which I don't ever do. And, as I've said, I haven't got a problem with the TV's tuner.

I understand what you're saying about uninterrupted signal path being more important than power output, but there are limits! For example, I can SEE the Leamington Spa transmitter from my house but it wouldn't be any use to me because - besides only carrying a few channels - its power output is diddly sqat. Having said that, about 20% of my neighbours have their aerials pointing at Lark Stoke (the rest being SC) so there must be an acceptable signal.

Thye more I think about it, the more convinced I'm becoming that something changed last December. Prior to that, the first Humax had worked perfectly ok for 15 months or so - and then suddenly this problem started happening. I've tried to eliminate everything I might have done to cause it - for example, by removing my power-line ethernet adapters. So what sort of external factors might there be? Some equipment or other installed by a neighbour? A new building along the signal path? [To have any effect, that would probably need to be within the final 3 or 4 miles where the ground clearance is low, and I'm not aware of anything.

link to this comment

jb38: I think we may be getting somewhere. I have also been discussing my problem on one of the Humax-related forums, and some of the people there have been suggesting that I may have too much or too little signal, and that some experimentation with additional amplifiers and/or attenuators may shed some light on the matter. Some were also pointing the finger of suspicion at the Wickes distribution amp.

The first thing I did was to connect an additional Micromark 12dB booster immediately before the Humax. This had the effect of raising the signal level from 55% to 72%, but made no difference to the quality. I then took the Wickes distribution amp out of circuit, joining its input and (the appropriate) output cables with a passive co-ax coupler. This reduced the signal level to about 60% BUT the quality was now rock steady at 100%, even on the troublesome muxes. I then removed the booster which I had just inserted. The signal level went down to 40-odd% BUT the quality remained at 100%

I've now installed the Mircomark booster in place of the Wickes amp for the Humax and main TV (with another output from the Micromark going into the Wickes amp for the other TVs). Incidentally the only other TV in frequent use is a 26" Philips with virtually identical innards to the main TV - and that had always been ok, and continues to be ok despite getting its signal from the Wickes amp.

So although I need to run with it for a bit longer and, in particular, give SWMBO a chance to break it ('cos it seems more likely to fall over when she's watching it!) before being sure that I've fixed it, I'm moderately optimistic.

If this turns out to be the case, it leaves the unanswered questions:
1. What is the Wickes amp doing which the Humax doesn't like but the Philips TVs don't mind?, and
2. Why did it suddenly start doing it only recently (after upwards of 25 years of faultless operation?

link to this comment

jb38: The Wickes distribution amp is extremely similar to one currently available from Screwfix, and has a lead which plugs directly into the mains. See:
Labgear MSA262/S Distribution Amplifier 2 Input 6 Output |

I'm not sure why you assume that I don't have a simple test meter - I have several! I have just plugged a flylead into the (now vacant) outlet socket to which the Humax had used to be connected, and applied my digital multimeter to the other end. On either AC or DC it reads 0.00 mV

I guess that I would need a very high frequency scope (which I don't have!) to be able to look for noise on the output signal. Is it possible that a capacitor in its power supply could have gone tits up after 25 years and started to generate noise? (CV358SE)

link to this comment

jb38: I don't think there was any risk of the Humax input being overloaded. The gain of the Wickes amp is only 6dB. The Humax was reporting 50-55% signal strength. The amp which I'm now using is 12dB and the Humax is reporting 72% And the quality is a rock-steady 100% on all muxes (which it was, even at a lower signal level once I had removed the Wickes amp from the equation)

Ian: The amp is actually in an upstairs bedroom/office rather than the loft, but that's not important. It has both TV and FM radio inputs, which it distributes to various points around the house - hence the 6 outputs. Two of these are currently used for TVs and two for radios, and the others are in position where we might want one or the other at various times.

And yes, I'm now using two amps. The additional amp has one input and 3 outputs - 2 of which are in use. The input is connected to the aerial. One of the outputs goes to the Humax and its connected TV, and another output goes to the Wickes amp's UHF input - so that will continue to do everything it's always done EXCEPT for supplying the Humax.

link to this comment
Page 1