Strange Happenings on Retuning a Digi Box
 

In message , Bill Wright
writes
Ian Jackson wrote:
In message , r brooks
writes

"Bill Wright" wrote in message
...
Gareth Davies wrote:

There is a solution but one way is to have your aerial realigned.


Because of the extreme sensitivity of many modern DTT receivers this is
unlikely to help, unless the aerial was grossly wrong in the first
place.

Bill

------------------------------------------------------------------------
-----------------

Conclusion:

Bought a variable attenuator on line for £3.15 inc postage. screwed
it out
for maximum resistance (less one complete turn out of five turns) and it
eliminated all channels in the 800 range on the factory default/automatic
retune.

Many thanks to all for helping me get good results.

Good conclusion. You can take it out until you do another scan.

I usually leave it in as long as long as the wanted channels are plenty
strong enough.

If you leave it in, and there's only a few dB between the wanted and the
unwanted, if the wanted drop a little, they may become marginal, and
you'll find that some channels drop out at times.

People forget to use it when they do a retune

OK, so maybe leave it connected in circuit as a reminder, but turn it to
minimum attenuation.

, and it could help with 4G (etc) problems.

Maybe (when it's a case of severe overload). On the other hand, the
relative levels of the TV and 4G signals won't change as you twiddle the
attenuator. I suppose it depends on the mechanism of the interference.
--
Ian

Strange Happenings on Retuning a Digi Box
 

Ian Jackson wrote:

I usually leave it in as long as long as the wanted channels are
plenty strong enough.

If you leave it in, and there's only a few dB between the wanted and the
unwanted, if the wanted drop a little, they may become marginal, and
you'll find that some channels drop out at times.
Yes agreed, but see below.

Maybe (when it's a case of severe overload). On the other hand, the
relative levels of the TV and 4G signals won't change as you twiddle the
attenuator. I suppose it depends on the mechanism of the interference.

I was really thinking, I suppose, about the situation where the
attenuator is on the input to the distribution amplifier. In that case
it could very likely reduce 4G problems. That would be the best place
for it as long as there is a largish ratio between the wanted and
unwanted TV signals. That is the most common situation after all. Given
the extreme sensitivity of many modern receivers it is quite common to
have channels appear in the 800s that are from muxes 40dB or more below
the wanted signals.
Bearing in mind the directional properties of the aerial, if the said
aerial is properly installed and is not a turd on a stick there should
almost always be a large ratio between the wanted and unwanted signals.
Consider the case where the wanted and unwanted signals are of the same
field strength. The directional properties of the aerial should be able
to provide a decent ratio between them. The exception would be when they
come from the same direction and have the same polarisation.
Another exception is when reception is from a distant transmitter (most
likely a main station) but there is a local relay close by. The relay
cannot be used because it is Freeview Lite or because signals are
hoplessly garbled by reflections. This happens in some of the urban
areas near the Crosspool mast, where trees and topography conspire to
deliver to some locations massively strong muxes that are mangled to
death. Even if they are decodable they are unreliable. Aerials look
towards Belmont, so passive filters are no help. At one recent job at a
sheltered scheme we found the aerial producing signals from Crosspool
that were dancing up and down and all over the place, but were around
10dB stronger than the (wanted) Belmont signals. This was only 2km from
Crosspool but screened by trees on a high bank. The aerial was one of
the popular huge wideband high gain things (it was a Superbo Antennisimo
Fantastico Gereralisimo Grandioso with 164 elements and a built-in
microvolt maximiser, as I remember). We installed two log periodics
phased together, and achieved far better results. This sort of thing:
http://www.wrightsaerials.tv/ourwork/018.shtml but the spacing was
arbitrary because the ****e (Crosspool) was coming at us from all
directions.


Bill

Strange Happenings on Retuning a Digi Box
 

Bought a variable attenuator on line for £3.15 inc postage. screwed
it out
for maximum resistance (less one complete turn out of five turns) and it
eliminated all channels in the 800 range on the factory default/automatic
retune.

Many thanks to all for helping me get good results.

Good conclusion. You can take it out until you do another scan.

I usually leave it in as long as long as the wanted channels are plenty
strong enough.

If you leave it in, and there's only a few dB between the wanted and the
unwanted, if the wanted drop a little, they may become marginal, and
you'll find that some channels drop out at times.

People forget to use it when they do a retune

OK, so maybe leave it connected in circuit as a reminder, but turn it to
minimum attenuation.

, and it could help with 4G (etc) problems.

Maybe (when it's a case of severe overload). On the other hand, the
relative levels of the TV and 4G signals won't change as you twiddle the
attenuator. I suppose it depends on the mechanism of the interference.

Though sometimes if the level of the interferer can be taken down enough
so that it doesn't drive the RX frond end into distress then that can be
useful to permit reception of the weaker signal..

Bill W might know isn't there a new box out that you can prog your
postcode into and it only tunes the allocated TX for that area?..
--
Tony Sayer

Strange Happenings on Retuning a Digi Box
 

In message , tony sayer
writes
Bought a variable attenuator on line for £3.15 inc postage. screwed
it out
for maximum resistance (less one complete turn out of five turns) and it
eliminated all channels in the 800 range on the factory default/automatic
retune.

Many thanks to all for helping me get good results.

Good conclusion. You can take it out until you do another scan.

I usually leave it in as long as long as the wanted channels are plenty
strong enough.

If you leave it in, and there's only a few dB between the wanted and the
unwanted, if the wanted drop a little, they may become marginal, and
you'll find that some channels drop out at times.

People forget to use it when they do a retune

OK, so maybe leave it connected in circuit as a reminder, but turn it to
minimum attenuation.

, and it could help with 4G (etc) problems.

Maybe (when it's a case of severe overload). On the other hand, the
relative levels of the TV and 4G signals won't change as you twiddle the
attenuator. I suppose it depends on the mechanism of the interference.

Though sometimes if the level of the interferer can be taken down enough
so that it doesn't drive the RX frond end into distress then that can be
useful to permit reception of the weaker signal..

Where something is being driven into nonlinearity by a strong signal,
it's nonlinear for all signals, and the addition of a front-end
attenuator is a well-established possible cure for a multitude of
problems.

Bill W might know isn't there a new box out that you can prog your
postcode into and it only tunes the allocated TX for that area?..

That could lead to problems when the signal from your assigned TX
is poor where you live, and you have to receive another. You would have
to fiddle things by using a false postcode - one for the area definitely
covered by TX you actually wanted to tune to (like you can do with
Freesat if you want a specific ITV area local content). Maybe every TX
should have had a 'tune to me' code for you to enter. On the other hand,
it's probably a darn sight easier for every TV receiver and STB to be
obliged to have manual tuning.
--
Ian

Strange Happenings on Retuning a Digi Box
 

tony sayer wrote:

Bill W might know isn't there a new box out that you can prog your
postcode into and it only tunes the allocated TX for that area?..

Most of them now ask for your country and region. Unfortunately they
often then go on to ignore the information. I don't know whether this is
the fault of the receivers or the givers.


Bill

Strange Happenings on Retuning a Digi Box
 

On 19/01/14 13:36, Ian Jackson wrote:
In message , tony sayer
writes
Bought a variable attenuator on line for £3.15 inc postage. screwed
it out
for maximum resistance (less one complete turn out of five turns)
and it
eliminated all channels in the 800 range on the factory
default/automatic
retune.

Many thanks to all for helping me get good results.

Good conclusion. You can take it out until you do another scan.

I usually leave it in as long as long as the wanted channels are plenty
strong enough.

If you leave it in, and there's only a few dB between the wanted and the
unwanted, if the wanted drop a little, they may become marginal, and
you'll find that some channels drop out at times.

People forget to use it when they do a retune

OK, so maybe leave it connected in circuit as a reminder, but turn it to
minimum attenuation.

, and it could help with 4G (etc) problems.

Maybe (when it's a case of severe overload). On the other hand, the
relative levels of the TV and 4G signals won't change as you twiddle the
attenuator. I suppose it depends on the mechanism of the interference.

Though sometimes if the level of the interferer can be taken down enough
so that it doesn't drive the RX frond end into distress then that can be
useful to permit reception of the weaker signal..

Where something is being driven into nonlinearity by a strong signal,
it's nonlinear for all signals, and the addition of a front-end
attenuator is a well-established possible cure for a multitude of problems.

Bill W might know isn't there a new box out that you can prog your
postcode into and it only tunes the allocated TX for that area?..

That could lead to problems when the signal from your assigned TX
is poor where you live, and you have to receive another. You would have
to fiddle things by using a false postcode - one for the area definitely
covered by TX you actually wanted to tune to (like you can do with
Freesat if you want a specific ITV area local content). Maybe every TX
should have had a 'tune to me' code for you to enter. On the other hand,
it's probably a darn sight easier for every TV receiver and STB to be
obliged to have manual tuning.

In case of strong wanted and unwanted the trick is to align the antenna
- a good directional one, - so the unwanted coincides with one of the
nulls in the lobe pattern. Getting the main signal 'on beam' is far less
important than getting the unwanted signal 'off beam'

with luck you can also attenuate the main beam enough not to need
reduction either.

using a laptop with a tuner dongle in it up in the loft or even on the
roof is a way to do all this.


Though you would have to be very close to a transmitter to get into
front end overloading.

I've had no problems a couple of miles from e.g sandy heath..


--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.