Poor signal on some channels

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Poor signal on some channels

(5 posts)

voxmagna

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My box is 3 weeks old. Recently I started getting bad pixelation on one MUX channel 32. I checked the signal properties as follows (brilliant Humax!) Menu/Settings/System/signal detection.

My results from Rowridge were Ch28 S62 Q100%, Ch30 S63 Q40%, Ch32 S61 Q10%, Ch33 S50 Q100%, Ch34 S52 Q100%, Ch 37 S55 Q100% You don't worry too much about signal strength (S),it's the decode quality (Q%)that's more important.

Obviously something is wrong on Channels 30 and 32. But there are no problems decoding those channels on 3 other Freeview TV/boxes. What's up doc?

I wiggled the rf flylead in the Humax antenna socket and those channels came good. A few days later, the problem came back. I carefully looked at the r.f fly lead I had made up with a soldered centre pin, and everything tested ok and the same lead worked on 3 other receivers. The one thing I wasn't happy about was the TV co-ax I got from Maplin. I've worked in rf all my life and that co-ax sure has very little copper screen on it!

My house is wired for terrestrial TV with a distribution amp in the loft and all drops to wall plates are done in CT125 satellite cable - The Bees Knees, with a decent size copper centre and both copper braid and foil outer sheaths.

It's a little inflexible to use as TV fly leads, but since my TV is on a stand and doesn't get moved about much, I decided to re-make my flylead using CT(SAT)125.

I also had a peek inside the Humax box. The tuner and distribution amp for the rf loop through, sit verticallly behind the rear panel. The rear panel antennae connector holes are just larger than the connectors and on the rear panel they put some kind of conductive foam to bridge the antenna input and loop out connectors. When I wiggled my fly lead, I was actually causing their connector outer body to touch the rear panel and make a second rf ground(??)

My new fly lead with plenty of copper screen works perfectly (although not so flexible). My new results were as follows:

Ch28 S63 Q100%, Ch30 S63 Q100%, Ch32 S61 Q100%, Ch33 S51 Q100%, Ch34 S54 Q100%, Ch 37 S558 Q100%

I don't believe the 'rejection notch' in the channel group frequency response was solely due to my cheaper fly lead, as it worked fine with 3 other receivers and had showed good decode quality across all muxes.

I think there could be a nasty RF grounding problem, but I'm too old and tired to drag out the spectrum analyser, sig gen. and reflectometer to look for spurii or return loss problems on their RF IO.

In this fault finding process, I had the Humax powered down and was very disappointed to find it it had not remembered the scheduled recordings I had spent some time entering!

| Fri 6 Jan 2012 1:45:05 #1 |
FenderBender

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Thanks voxmagna for a detailed post. I think poor quality cabling is responsible for most reception problems.

I have the standard coax from a dist amp in my loft to 4 points around the house. This was installed by the house builder, so they used the cheapest they could find. Its not been bad, considering I'm 65 miles from Winter Hill and I have 2 amps in line to boost the signal (and any interference!).

I recently changed the dist amp to increase the number of available ports (kids want TV in their rooms these days). After that, my trusty HD Fox T2 in the kitchen produced more-than-average pixellation. A quick visit back to the loft and I discovered there was a single strand of braid wrapped around the core inside the connector for the kitchen coax. I removed that and the picture is perfect again.

| Fri 6 Jan 2012 8:54:26 #2 |
grahamlthompson

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Baffled why your HDR lost it's recording schedule. They are stored on the hard disc. Did you by any chance run a autotune or carry out a system reset. Either deletes the recording schedule, simply powering the unit off should not.

| Fri 6 Jan 2012 10:35:45 #3 |
voxmagna

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grahamlthompson - 52 minutes ago »
Baffled why your HDR lost it's recording schedule. They are stored on the hard disc. Did you by any chance run a autotune or carry out a system reset. Either deletes the recording schedule, simply powering the unit off should not.

OK, thanks you hit the right spot. Thinking the tuner could have lost its preset on by bad channels I did do an autoscan. Repeating the autoscan on the same channel group, I didn't expect my schedules to get wiped and as you say, they should be on the HDD or in NVRAM.

I checked my signals this morning and all are now solid. for me, they should get better in March because Rowridge is one of the last to get it's channel change and power increases. Then I may be able to get better SD Freeview mobile in my car radio which just locks static on a wing and a prayer, and I can watch some terrestrial HDTV at home.

I've seen a couple of posts here about signals and blocking. What confused my wife was the on screen error message she saw about the channel being 'scrambled'. Funny they should use that for poor signal quality on a FTA channel.

The built in Humax signal level and quality tester worked for me and I was pretty impressed it helped find a solution. But I'm still curious about their grounding, isolation between the RF IO modules and the sticky piece of conductive foam that sits between the two connector screens. That seems to be what they are using to ground the tuner and loop through to the plated rear panel (?). If there is an issue in that area, it will be hard for most to work out, because it could be frequency selective in nature and they will be told it's an aerial or feeder fault.

| Fri 6 Jan 2012 11:48:02 #4 |
Watt Tyler

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voxmagna - 39 minutes ago »

I checked my signals this morning and all are now solid. for me, they should get better in March because Rowridge is one of the last to get it's channel change and power increases. Then I may be able to get better SD Freeview mobile in my car radio which just locks static on a wing and a prayer, and I can watch some terrestrial HDTV at home.

Have you caught up with the fact that, post DSO, Rowridge will be transmitting both horizontally and vertically polarised signals, with the stronger ones being vertical? [Something to do with not interfering with the Frogs.]

You should still be ok, though, without moving your aerial because even the HP signals will be a lot stronger than at present. You will, of course, have to re-tune because they're moving the muxes onto different channels.

| Fri 6 Jan 2012 12:33:00 #5 |