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All posts by Mike

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

M
Oxford (Oxfordshire, England) Full Freeview transmitter
Wednesday 18 April 2012 2:55PM
Swindon

to Robert who said "I have just looked at the various transmitters available to us at SN3 4ST and the two Mendip ones are just 7 kilometers away, and yet the predicted channel reception is only good on 4 Coms, whereas Oxford is green on all. "

Your location in Vicarage Lane, South Marston, Swindon is much closer to Oxford than Mendip transmitter. The Mendip transmitter is more like 70 km away rather than 7km (4.3 miles).

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GB

Just discovered, the hard way, that programme 25 (Dave ja vu) has been moved from channel 59- (ArqA) to Channel 62 (SDN) so you need to re-tune. List of programmes against channels above need updating.

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GB

In reply to the question about the impending loss of Film 4 on channel 15, you can see from the list at the start of the page that it has moved to PSB2.

Manually retune C60 and C55 to get back Film 4 on 15 and a bonus of Film 4+1 too on 45.

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GB
P
Oxford (Oxfordshire, England) Full Freeview transmitter
Saturday 28 September 2013 1:58PM
Swindon

Like the people above, I found that channel 44 (5+1) and others disappeared soon after 6pm last night. Further investigation showed that both RF 50 and RF 59 were down to a very low level so eliminating all programmes multiplexed on COM 4 and COM 5. Deeper investigation showed it was not a weather related problem as there was no sign of signal strength reduction on other frequencies. That just leaves the cause as power reduction at the transmitter or someone had realigned the antennae on the mast. Perhaps the authority would like to comment now, and next time put up a post when a problem occurs rather than just leaving up the default "no problems" message.
It was still the same when I went out at 9am but was back to normal when I returned soon after 1pm.

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GB
P
Oxford (Oxfordshire, England) Full Freeview transmitter
Sunday 10 November 2013 11:34AM
Swindon

I was about to post about the filter location and then saw the last line of the post above.

A filter should always be placed after the aerial and before the amplifier. The reason is that if placed after the amplifier, the amplifier input will try to amplify the strong unwanted signal (4G CH 60 in this case) and the amp can be overloaded. The result of that is is non-linear operation, possibly creating new unwanted interference on other frequencies, and with some amps, an automatic reduction of gain across the whole frequency range.

Go into the loft and place the filter before the amplifier and let us know the result.

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GB

As moving the tv or changing lead length makes so much difference and as you are relatively close to the transmitter, don't rule out the possibility that there is a break in the coax lead from the aerial to the set. The signal you are getting may be just the coax acting as the aerial, thus giving differences in signal strength as you change coax length and position. A break will also give you different effects on each frequency as it will not be a 75 Ohm match

It is very easy to test with a multimeter. At the aerial end, join the inner and outer of the coax and then at the set end use a multimeter (or even a battery and torch bulb) to check for continuity between the inner and outer of the coax.

I have seen this before and the lack of a shield on the wire (in effect) also produces resonance at strange frequencies. Check continuity also at your spurs to other sets as a break in their coax will act as another input on a different (interfering) frequency.

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GB

A break in the coax means you have an unterminated length of wire that is resonant at a frequency that is set by its length and the velocity factor of the wire. This can enhance or nullify signals at one frequency. Worth a check as it is simple to do.

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GB

Rob, you said "Not sure what's going on there, is something strange happening in the cable under the floor? "

Did you do the simple cable continuity check I suggested earlier? You could do this now on just the cable under the floor using a torch bulb and battery.

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GB

Hi Rob, you said "Hi Pikpilot,
Sorry if i am honest i did not really understand how to do this, i have a coax plug into the wall socket, a run of cable under the floor, a two way splitter which feeds one lead to the TV and one lead to a spare socket at the other end of the room. Could you explain this test is laymans terms for me, i have no experiance of this kind of thing. "

What I said in earlier posts is that you should check the continuity of each of your cables. Easiest way is, at one end of the cable (without the splitters in) join together the inner and outer (pin and case) of the cable. At the other end either use a multimeter, or if use don't have one, use a torch battery and bulb in series across the pin and outer of the cable. The bulb will light if no fault.

I have come across a number of installations where people had not soldered the inner wire of the cable into the pin of the plug. What happens is that the wire does not actually touch the inside of the pin and the signal is only capacitively coupled. Sounds unbelievable but it happens when the wire is too short to reach the end of the pin and is held central by the insulation. If you don't want to solder it then there is another fix that works. Just put a kink in the inner wire before you push it into the pin of the plug. With all those splitters in place you are already loosing a lot of signal so a single connector problem will be the last straw. And it is not just about signal loss as a break in the cable will make the cable look like an un-terminated long wire aerial bringing in interference.

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GB

Rob, don't take the connectors off as we are looking for a poor connection in the connector.
If you have taken the connectors off the when you put them back do this;
1) put a small kink in the central wire to ensure it is making contact inside the pin
2) after putting it back together, connect your multimeter on the ohms range between the inner and outer of the connector. It should read Infinity.
3) do the test in my previous post but using the multimeter instead of a battery and torch bulb. Reading should be around zero ohms

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GB
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