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Saturday, 2 June 2012
J
jb38
sentiment_very_satisfiedPlatinum

7:47 PM

Mazbar: Yes, as anyone situated too close to a transmitter mast can suffer from what's generally known as the "umbrella" effect, this demonstrated perfectly by the fact that if in a mobile situation (with passenger to monitor the meter) and using a mast of a reasonable height (main station mast) as the target, that if a test signal strength reading is taken from roughly five miles or so away from the mast and you then start driving towards it taking readings along the way, it will be found that although the signal level "might" (depending on starting distance) initially be observed to increase, that at certain point along the route towards the mast the situation will reverse whereby the signal will stabilise then slowly start to decrease the closer you get to the target, and of course caused by what you have mentioned.


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jb38's 7,179 posts GB
R
Robert
9:19 PM

JB38: You make some very interesting observations. All my poratble TV's use a straight radio type aerial so a loop aerial is not to hand. My main TV is in the living room which has large windows from which I can see the trasnmitter mast at the top of the hill. I have had a decade of perfect Freeview reception and made he last change to the coniguration of my AV equipemnt in Oct 2011. Everthing worked and was 'rock solid' until April 4th. I will follow your suggestions when I have some 'I/O' time or 'downtime' with he system as I watch TV in timeslip with the HDR set to record everything I might want to watch days ahead. I've manage to get though 2 of the 3 Lord of the Rings films on CH4 HD without error. My professional background is trouble shooting Mini computer errors especially disc drives. Although I later switched to Oracle databases. Your help is appreciated.

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Robert's 20 posts GB
Sunday, 3 June 2012
S
Stephen P
sentiment_satisfiedGold

1:41 AM

My professional background is trouble shooting Mini computer errors especially disc drives.

Does that mean you can mend my PVR ?

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Stephen P's 1,172 posts GB
R
Robert
8:52 AM

I did repair a friend's Thompson DHD4000 is was not booting up and giving no video o/p. Once cracked open, I heard a tell tail click click from the hard drive. Power supply! so I powered the disc from another supply and the thing burst back into life. According to the internet weak PSUs are a known problem and i found a capacitor kit for the PSU which I then fitted. But it took months to do the final physical repair. I also have my own Thompson DHD4000 and Lite-on LVW-5045 which are both sick and need repair waitting for me.

So what's the problem?
and can you fix 'my' transmitter for me?

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Robert's 20 posts GB
S
Stephen P
sentiment_satisfiedGold

10:30 AM

Its a Wharfdale something. Seems to work OK; then shuts down. I have unplugged the HD and still same.

I give up on your problem, which I presume is related to proximity. Did you try nothing at all in the aerial input? Or just a fly lead?

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Stephen P's 1,172 posts GB
T
Tony Kendrick
10:34 AM

I live in Littlehampton and have a 52 element roof mounted aerial installed six years ago. In spite of living a mile from the coast and receiving Rowridge mostly over open water reception was fine. But after the 18 April switchover when the COM5 mux moved to Ch21 signal quality dropped to between 5% and 25% while signal strength is high so often drops out altogether. The other commercial muxes have 90+% signal quality and strength.

Is this an inversion problem or could the 200k signal on Ch 21 be causing cross channel interference (I haven't got a T2 tuner yet so dont get the HD mux)?

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Tony Kendrick's 1 post GB
Dave Lindsay
sentiment_very_satisfiedPlatinum

12:20 PM

Tony Kendrick: I think that the most likely solution is to change your aerial to vertical.

Other people have posted on this site saying that they have changed their aerials and that it has rectified the problem.

That may be a costly exercise if you can't do it yourself.

"Maybe" some attenuation to reduce the level of signals might help. Whether it will work will depend on whether you can find a sweet spot where the higher power signals are reduced enough but the lower ones are reduced too much.

This is probably exacerbated by the fact that the powers that be decided to put the low power (50kW) horizontal signals on adjacent channels to the relatively high power (200kW) horizontal signals.

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Dave Lindsay's 5,724 posts GB
Monday, 4 June 2012
R
Robert
10:06 AM

There were 3 big films on Saturday on HD the Mux. I got about 2 hrs into Lord of the Ring, just after Brian Blessed did some shouting in the advert break and it started raining in Crystal Palace. Un watchable TV.
It's been raining and dull so I have nothing but dammaged video since.

I found my Fringe electronics PRO TV & Sat Signal Finder. The aerial into the HDR is 62 dBuV, Aerial into TV 74 dBuV and the 12" Wire 71 dBuV at TV aerial socket. They say 59-78 dBuV is OK.

HDR is more sensitive and susceptible that the TV but produces a much better picture across the board. The TV indicates the RF is producing bad video. Ive only just discovered were the signal condition monitor is on the TV menus so I can measure a bit rate error. Other times Ive seen signal Quality Red (1) and perfect vision and sound. When TV & HDR shared aerial, perfect Video on TV and HDR unable to find the Mux.

Dave Lindsay: Attenuation was an early theory and I have posted about reducing attenuation. Measuring the actual signal at 0dB attenuation show it to be at lower end of optimal.

Mazbar: I do have access to an outdoor aerial via a communal aerial system (74 dBuV). The problem is that ever since the days of three channel TV, I have always got a better picture by using an indoor aerial. Analogue Cable TV offered no advantage, despite claims. I have checked since but I still think the indoor aerial is superior although not as neat. I know that in my block and the next block the communal aerial systems have exactly the same problem. Both were considered working before but not after DSO. Set up for HD (Oct 2011) was no problem at all and has been rock solid until DSO1.

JB38: Did the wire test yesterday while it was raining. In the TV it gave a very similar picture and measured 80 compared 73 on a wedge type indoor aerial, the one I was using on the HDR (shared) since Oct. The lowest reading was 63 for BBC1 and 90 for ITV1.

Swapping to the HDR The wire gave a predominantly yellow signal quality against a Green quality for the aerial, the Picture was bordering on unwatchable for the aerial but being give a steady full marks (10) for quality for that channel. The Skys clear so I cannot check at the Mux level. I have fired an email asking for an advanced user guide to explain what this diagnostic is supposed to indicate as I not getting consistent results. Other times the quality signal bounces around all over the place all.

Both the TV and HDR crash out with no signal if nothing is plugged in.

Thanks for all your help. Suggestion always welcome.




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Robert's 20 posts GB
J
jb38
sentiment_very_satisfiedPlatinum

4:45 PM

Robert: Thanks for your latest update, and all said noted.

PSB1/BBCA started at 200Kw on Ch23 and if anyone situated relatively close to the station could not receive it on an indoor aerial then it was most likely because that the signal strength received was still too high for the tuner in the receiver to cope with, this being very dependant on the brand of device used as well as its screening ability as far as resisting high powered RF signals being picked up directly by its internal circuitry, PVR's usually being better in this respect because of them being contained in a metal casing.

Of course in these type of situations other peculiar effects such as apparent null points can be observed if one wanders around in decreasing circles with a signal meter strung around their neck, but every situation is different for a variety of reasons making it whereby no one single answer is ever possible, and with this being why RF engineering gets classed as a "black art", as problems are generally sorted out as they are found, as its impossible to forecast every eventuality in advance.

Regarding your wire aerial test, what you have reported roughly tally's up with what I expected, but the only downside of that type of test is, that although the signal strength is at a more acceptable level for the receiving equipment it is however very susceptible to fluctuations from movement close by, and this does not necessarily mean in your own apartment but those adjoining it.

To be able to get a better idea of the situation you could try a much more reliable test, and for which you will require a short length of coax enough to stretch between the TV's aerial socket and your window ledge, the coax braid and core at the window ledge end being connected into an electrical (5amp) terminal strip. You then require a stiff piece of wire to construct a small loop having a maximum diameter of about 6" or so and connect this into the terminal strip, thereby in effect constructing a small loop aerial.

Temporarily fix this just inside the window ledge so that the signal received has the very best chance of NOT being affected by movements from within the room nor suffer if the walls of the property are wet should it have happened to rain, but leave the TV on its signal checking screen (channel you watch most) whilst you are fixing the loop with the best orientation for reception.



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jb38's 7,179 posts GB
J
jb38
sentiment_very_satisfiedPlatinum

8:37 PM

Robert: Just in case you were wondering, the first two paragraphs of this reply is in answer to the question you asked under the other thread heading of: "Freeview on the Crystal Palace transmitter".

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jb38's 7,179 posts GB
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