Band pass filters -- what am I missing?
 

I'm in an area served by two transmitters, one group A, the other group
B. The weaker group A stuff is being picked-up from the back of the
aerial. As a result, whenever I re-tune my DTV boxes the weaker channels
get allocated the lower numbers, the correct channels the 800 range. If
I insert a group B band pass filter into the downlead before it gets to
the tuner I still get the group A channels, albeit that they now are in
the 800 range. I was under the impression that a bandpass filter was
supposed only to pass signals on the stated band. That's not the case as
I see it. what am I missing here please?


Cheers


Clem

Band pass filters -- what am I missing?
 

Clem Dye wrote:
I'm in an area served by two transmitters, one group A, the other group
B. The weaker group A stuff is being picked-up from the back of the
aerial. As a result, whenever I re-tune my DTV boxes the weaker channels
get allocated the lower numbers, the correct channels the 800 range. If
I insert a group B band pass filter into the downlead before it gets to
the tuner I still get the group A channels, albeit that they now are in
the 800 range. I was under the impression that a bandpass filter was
supposed only to pass signals on the stated band. That's not the case as
I see it. what am I missing here please?

What make/type filters are they, and what are the two transmitters concerned ?

--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

Band pass filters -- what am I missing?
 

In article ,
Clem Dye wrote:
I'm in an area served by two transmitters, one group A, the other group
B. The weaker group A stuff is being picked-up from the back of the
aerial. As a result, whenever I re-tune my DTV boxes the weaker channels
get allocated the lower numbers, the correct channels the 800 range. If
I insert a group B band pass filter into the downlead before it gets to
the tuner I still get the group A channels, albeit that they now are in
the 800 range. I was under the impression that a bandpass filter was
supposed only to pass signals on the stated band. That's not the case as
I see it. what am I missing here please?


the filter will reduce the level of the unwanted, but probably, unless its
very expensive, not remove them altogether. You could try two filters in
series ...



Clem

--
From KT24

Using a RISC OS computer running v5.16

Band pass filters -- what am I missing?
 

The box should automatically put the weakest signals in the 800 range, so it
sounds like your Group A signals are quite strong. Maybe you should be
pointing towards the Group A signals. Depending on which filter you've got,
the out of band rejection might be as little as 15dB so filtering is just
reducing the Group A signals to below the level of the Group B ones. Why not
just manually tune each mux, or unplug the aerial feed until it's passed the
Group A channels.



"Clem Dye" wrote in message ...

I'm in an area served by two transmitters, one group A, the other group
B. The weaker group A stuff is being picked-up from the back of the
aerial. As a result, whenever I re-tune my DTV boxes the weaker channels
get allocated the lower numbers, the correct channels the 800 range. If
I insert a group B band pass filter into the downlead before it gets to
the tuner I still get the group A channels, albeit that they now are in
the 800 range. I was under the impression that a bandpass filter was
supposed only to pass signals on the stated band. That's not the case as
I see it. what am I missing here please?


Cheers


Clem

Band pass filters -- what am I missing?
 

charles wrote:


the filter will reduce the level of the unwanted, but probably, unless its
very expensive, not remove them altogether. You could try two filters in
series ...

Even very expensive filters won't do that. All real world engineering
devices have limitations.

Band pass filters -- what am I missing?
 

On 27/08/2011 18:22, Clem Dye wrote:
I'm in an area served by two transmitters, one group A, the other group
B. The weaker group A stuff is being picked-up from the back of the
aerial. As a result, whenever I re-tune my DTV boxes the weaker channels
get allocated the lower numbers, the correct channels the 800 range. If
I insert a group B band pass filter into the downlead before it gets to
the tuner I still get the group A channels, albeit that they now are in
the 800 range. I was under the impression that a bandpass filter was
supposed only to pass signals on the stated band. That's not the case as
I see it. what am I missing here please?

A simple solution in some cases is to unplug the aerial when tuning for
the bit of the spectrum you are not interested in. Hence if wanting to
filter group A, start the scan with no aerial, wait until the progress
meter indicates you are up into the mid 30s (or guestimate it if its a
progress bar), and plug the aerial back in. Often simpler than trying to
sort out a mess of weak channels later.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Band pass filters -- what am I missing?
 

On Sat, 27 Aug 2011 19:22:01 +0100, John Rumm
wrote:

On 27/08/2011 18:22, Clem Dye wrote:
I'm in an area served by two transmitters, one group A, the other group
B. The weaker group A stuff is being picked-up from the back of the
aerial. As a result, whenever I re-tune my DTV boxes the weaker channels
get allocated the lower numbers, the correct channels the 800 range. If
I insert a group B band pass filter into the downlead before it gets to
the tuner I still get the group A channels, albeit that they now are in
the 800 range. I was under the impression that a bandpass filter was
supposed only to pass signals on the stated band. That's not the case as
I see it. what am I missing here please?

A simple solution in some cases is to unplug the aerial when tuning for
the bit of the spectrum you are not interested in. Hence if wanting to
filter group A, start the scan with no aerial, wait until the progress
meter indicates you are up into the mid 30s (or guestimate it if its a
progress bar), and plug the aerial back in. Often simpler than trying to
sort out a mess of weak channels later.

Surely even simpler is to find out the channel numbers for the
transmitter you want and do a manual scan for these specific channels?

http://www.ukfree.tv/transmittersmenu.php will provide the details.

Band pass filters -- what am I missing?
 

On Sat, 27 Aug 2011 20:02:55 +0100, Bob Latham
wrote:

In article ,
Scott wrote:
On Sat, 27 Aug 2011 19:22:01 +0100, John Rumm
wrote:

Surely even simpler is to find out the channel numbers for the
transmitter you want and do a manual scan for these specific channels?

But what about devices that do not have a manual tune facility?

Bob.

That would be different. I thought they all had. Certainly 3/3 of
mine have manual scanning.

Band pass filters -- what am I missing?
 

"Scott" wrote in message ...



That would be different. I thought they all had. Certainly 3/3 of
mine have manual scanning.

Ok so one does a manual set like I did but every day we turn on we are asked
to do a re-scan because of the over power full Belmont CH 22.
Regards
David

Band pass filters -- what am I missing?
 

On Saturday, August 27th, 2011 at 20:02:55h +0100, Bob Latham asked:

But what about devices that do not have a manual tune facility?

Simple solution -- do not buy them.

Band pass filters -- what am I missing?
 

In article ,
David Woolley wrote:
charles wrote:


the filter will reduce the level of the unwanted, but probably, unless
its very expensive, not remove them altogether. You could try two
filters in series ...

Even very expensive filters won't do that. All real world engineering
devices have limitations.

and two filters in series will increase the attenuation. Been there, done
it, bought the T-Shirt

--
From KT24

Using a RISC OS computer running v5.16

Band pass filters -- what am I missing?
 

Here's a list of bandpass filters.

http://dl.dropbox.com/u/11023364/bandpass%20filters.doc

Bill

Band pass filters -- what am I missing?
 

On 27/08/2011 19:50, Scott wrote:
On Sat, 27 Aug 2011 19:22:01 +0100, John Rumm
wrote:

On 27/08/2011 18:22, Clem Dye wrote:
I'm in an area served by two transmitters, one group A, the other group
B. The weaker group A stuff is being picked-up from the back of the
aerial. As a result, whenever I re-tune my DTV boxes the weaker channels
get allocated the lower numbers, the correct channels the 800 range. If
I insert a group B band pass filter into the downlead before it gets to
the tuner I still get the group A channels, albeit that they now are in
the 800 range. I was under the impression that a bandpass filter was
supposed only to pass signals on the stated band. That's not the case as
I see it. what am I missing here please?

A simple solution in some cases is to unplug the aerial when tuning for
the bit of the spectrum you are not interested in. Hence if wanting to
filter group A, start the scan with no aerial, wait until the progress
meter indicates you are up into the mid 30s (or guestimate it if its a
progress bar), and plug the aerial back in. Often simpler than trying to
sort out a mess of weak channels later.

Surely even simpler is to find out the channel numbers for the
transmitter you want and do a manual scan for these specific channels?

http://www.ukfree.tv/transmittersmenu.php will provide the details.

If the box supports manual scan... and of those that do, some have an
annoying habit of erasing all the stored channels each time you manual
scan. Hence you can only tune one mux.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Band pass filters -- what am I missing?
 

On Saturday, August 27th, 2011 at 20:25:34h +0100, Charles explained:

Been there, done it, bought the T-Shirt

Was it made of Swiss Shield RF Shielding Fabrics?

Do you have a HEAVY DUTY FARADAY CANOPY over your bed?

Use SHIELDITTM SUPER to line a vest or a hat to protect your vital organs
from radiowaves and electric fields.

http://www.lessemf.COM/fabric.html

Note the comment about the woman wearing a scarf made from
EX-STATICâ„¢ CONDUCTIVE FABRIC.

Band pass filters -- what am I missing?
 

"Bill Wright" wrote in message ...

Here's a list of bandpass filters.

http://dl.dropbox.com/u/11023364/bandpass%20filters.doc

How much is a filter just to keep CH22 out of a band B area?
And can one get one at a retailer as we not all in the trade.
I did have a friendly Trade supplier but he sold out to a National company
and are now strictly trade only.
Regards
David

Band pass filters -- what am I missing?
 

David Bolton wrote:
The box should automatically put the weakest signals in the 800 range,

No, not necessarily ! Some receivers put the *first* transmissions they
stumble across on the primary LCNs, and whatever comes next at 800+

Invariably on these receivers if your 'unwanted' channels are lower in the UHF
band than the 'wanted' you end up with the wrong set in the wrong place.

--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

Band pass filters -- what am I missing?
 

David wrote:


"Bill Wright" wrote in message ...

Here's a list of bandpass filters.

http://dl.dropbox.com/u/11023364/bandpass%20filters.doc

How much is a filter just to keep CH22 out of a band B area?

It's not just Ch 22 you need to filter, Ch 28, 25, and 30 will all eventually
be at the same power. (28 and 25 already are, though 28 is the HD mux, and
will be invisible to non T2 receivers)

Welcome to the world of hight power overlapping DTT. Folk in the Manchester,
Liverpool, and Bristol Channel areas (to name but three) have been struggling
with this problem for a while.

--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

Band pass filters -- what am I missing?
 

In message , John
Rumm wrote

If the box supports manual scan... and of those that do, some have an
annoying habit of erasing all the stored channels each time you manual
scan. Hence you can only tune one mux.

And some boxes only add channels to the list when you scan so you first
have to reset to get rid of the previous scan information prior to new
scan.


--
Alan
news2009 {at} admac {dot} myzen {dot} co {dot} uk

Band pass filters -- what am I missing?
 

In article , Bill Wright
wrote:
Here's a list of bandpass filters.

http://dl.dropbox.com/u/11023364/bandpass%20filters.doc

Has anyone (independent of the makers) done measurements on them and put
the results onto the web?

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Band pass filters -- what am I missing?
 

In article ,
Mark Carver wrote:

Welcome to the world of hight power overlapping DTT. Folk in the Manchester,
Liverpool, and Bristol Channel areas (to name but three) have been struggling
with this problem for a while.

Why do TVs not let you simply choose a transmitter? There's an
identifier in the signal somewhere, because I've seen it displayed.

-- Richard

Band pass filters -- what am I missing?
 

Richard Tobin wrote:
Why do TVs not let you simply choose a transmitter? There's an
identifier in the signal somewhere, because I've seen it displayed.

(I'll get in quick, before Mark et al get back from their pre-Sunday lunch
pints ... ).

The identifier is for a transmitter *group*, not an individual transmitter.
So although I want to receive from Ilchester Crescent, the identifier still
says 'Mendip'.

André Coutanche

Band pass filters -- what am I missing?
 

David wrote:

How much is a filter just to keep CH22 out of a band B area?

How strong is channel 22, in absolute terms and relative to the weakest
wanted channel? If there is a lot weaker, simply using a broadband
attenuator may be enough.

And can one get one at a retailer as we not all in the trade.
I did have a friendly Trade supplier but he sold out to a National
company and are now strictly trade only.

Band pass filters -- what am I missing?
 

In article , André Coutanche
wrote:
Richard Tobin wrote:
Why do TVs not let you simply choose a transmitter? There's an
identifier in the signal somewhere, because I've seen it displayed.

(I'll get in quick, before Mark et al get back from their pre-Sunday
lunch pints ... ).

The identifier is for a transmitter *group*, not an individual
transmitter. So although I want to receive from Ilchester Crescent, the
identifier still says 'Mendip'.

Which of course leads to the "Why, Oh Why?..." question...

Why didn't they give each individual TX its own ID and allow the user to
tell the box to scan for a specified ID?

Too late now, I guess.

I also find it a PITA to 'rescan', so only do so when I find I need it to
access something. In my case I have three items. With each I have to
either:

A) Do an 'auto' scan with the antenna lead unplugged to blank the existing
info. Then do a 'manual' scan for each target channel.

or

B) Do an 'auto' with the antenna only pligged in during a carefully chosen
part of the scan.

B is quicker if I get it right. But A may end up being faster if I can't
judge B correctly.

It would be nice if a box did a scan and showed the user where there were
duplicates of mux and offer them a choice of which to assign the correct
'logical' channel numbers. But none of the ones I have do anything like
that.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Band pass filters -- what am I missing?
 

In article ,
Richard Tobin wrote:
In article ,
Mark Carver wrote:

Welcome to the world of hight power overlapping DTT. Folk in the
Manchester, Liverpool, and Bristol Channel areas (to name but three)
have been struggling with this problem for a while.

Why do TVs not let you simply choose a transmitter? There's an
identifier in the signal somewhere, because I've seen it displayed.

not really. I believe that (for instance) all Welsh transmiiters call
themselves 'Wenvoe'.

--
From KT24

Using a RISC OS computer running v5.16

Band pass filters -- what am I missing?
 

This is what you get when a designer is not a person living in the real
world of the general public.

Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"Alan" wrote in message
...
In message , John Rumm
wrote

If the box supports manual scan... and of those that do, some have an
annoying habit of erasing all the stored channels each time you manual
scan. Hence you can only tune one mux.

And some boxes only add channels to the list when you scan so you first
have to reset to get rid of the previous scan information prior to new
scan.


--
Alan
news2009 {at} admac {dot} myzen {dot} co {dot} uk

Band pass filters -- what am I missing?
 

In article ,
Jim Lesurf wrote:
In article , André Coutanche
wrote:
Richard Tobin wrote:
Why do TVs not let you simply choose a transmitter? There's an
identifier in the signal somewhere, because I've seen it displayed.

(I'll get in quick, before Mark et al get back from their pre-Sunday
lunch pints ... ).

The identifier is for a transmitter *group*, not an individual
transmitter. So although I want to receive from Ilchester Crescent, the
identifier still says 'Mendip'.

Which of course leads to the "Why, Oh Why?..." question...

Why didn't they give each individual TX its own ID and allow the user to
tell the box to scan for a specified ID?

Not so easy when the 'transmitter' is a transposer.

--
From KT24

Using a RISC OS computer running v5.16

Band pass filters -- what am I missing?
 

On Sunday, August 28th, 2011 at 14:49:07h +0100, Brian Gaff explained:

This is what you get when a designer is not a person living in the real
world of the general public.

Are you suggesting that designers of some digital converter boxes are not
people or that they live on another world?

Do they all commute to work on this world from Tralfamadore?

Band pass filters -- what am I missing?
 

On Sun, 28 Aug 2011 13:53:05 +0100, Jim Lesurf wrote:

Why didn't they give each individual TX its own ID and allow the user to
tell the box to scan for a specified ID?

In fact each multiplex from each individual transmitter does have
its own unique identity in any one geographical area -- the UHF
channel on which it is transmitted.

So one solution for "auto scan" would be to prompt the user to
enter the UHF channel name to be added to an editable list of
channels to be automatically scanned each time the "auto scan"
function is activated.

I also find it a PITA to 'rescan'

The problem being the loss of favorites if you have any.

Band pass filters -- what am I missing?
 

In article , J G Miller wrote:

So one solution for "auto scan" would be to prompt the user to
enter the UHF channel name to be added to an editable list of
channels to be automatically scanned each time the "auto scan"
function is activated.

There must be numerous ways that lists of channels for each
transmitter could be provided in a compatible way, for example over
MHEG.

-- Richard

Band pass filters -- what am I missing?
 

J G Miller wrote:
On Sun, 28 Aug 2011 13:53:05 +0100, Jim Lesurf wrote:

Why didn't they give each individual TX its own ID and allow the user to
tell the box to scan for a specified ID?

In fact each multiplex from each individual transmitter does have
its own unique identity in any one geographical area -- the UHF
channel on which it is transmitted.

So one solution for "auto scan" would be to prompt the user to
enter the UHF channel name to be added to an editable list of
channels to be automatically scanned each time the "auto scan"
function is activated.

That's fine, until the UHF channel allocations change ! I'm afraid not even
those can be taken for granted to remain the same, if you can work out what
they are in the first place ! Ofcom data often doesn't match Digital UK's, so
whose do you trust ? It's all a shambles quite honestly.

--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

Band pass filters -- what am I missing?
 

"Bob Latham" wrote in message
...
In article ,
Clem Dye wrote:
I'm in an area served by two transmitters, one group A, the other group
B. The weaker group A stuff is being picked-up from the back of the
aerial. As a result, whenever I re-tune my DTV boxes the weaker channels
get allocated the lower numbers, the correct channels the 800 range.

I discovered this afternoon that my father has exactly the same problem.

He has an apartment (Kidderminster) which is fed from a communal aerial
system. It is designed for Sutton Coldfield but now suddenly pulls in
wrekin but the channels are good enough for the tv to allocate the lower
numbers to it but they break up something awful. I am going to fit a band
B filter and I'm also going to try using a 12 db attenuator. After tuning
I will remove the attenuator. Hope that works but what a fuss.

I think it will cause havoc on Sept 7th when everyone there has to retune,
Wrekin is too strong and out of band.


Bob.

They really didn't think much when they wrote the Freeview receiver spec did
they.

--

Brian Gregory. (In the UK)

To email me remove the letter vee.

Band pass filters -- what am I missing?
 

"Richard Tobin" wrote in message
...
In article ,
Mark Carver wrote:

Welcome to the world of hight power overlapping DTT. Folk in the
Manchester,
Liverpool, and Bristol Channel areas (to name but three) have been
struggling
with this problem for a while.

Why do TVs not let you simply choose a transmitter? There's an
identifier in the signal somewhere, because I've seen it displayed.

Because they're designed by idiots?

--

Brian Gregory. (In the UK)

To email me remove the letter vee.

Band pass filters -- what am I missing?
 

On Sunday, August 28th, 2011 at 17:27:25h +0100, Mark Carver wrote:

That's fine, until the UHF channel allocations change !

Hence why I stated an "editable list".

so whose do you trust ?

UK Free TV? ;) ;) ;)

It's all a shambles quite honestly.

Totally agree - can you name any other country undergoing
digital switchover which has forced people to do more than
one retune?

Band pass filters -- what am I missing?
 

On Sun, 28 Aug 2011 16:13:58 +0000, Richard Tobin wrote:

There must be numerous ways that lists of channels for each transmitter
could be provided in a compatible way, for example over MHEG.

Yes but how does the user get the information via MHEG before the
first autoscan on a brand new box?

Band pass filters -- what am I missing?
 

J G Miller wrote:
On Sunday, August 28th, 2011 at 17:27:25h +0100, Mark Carver wrote:

That's fine, until the UHF channel allocations change !

Hence why I stated an "editable list".

Well, you're almost back to a 'manual tune' procedure then ? In other words
you have to know which transmitter you're using, and what its UHF allocations
are (at present!). In other words you need to be 'technically minded' in order
to perform a retune.

so whose do you trust ?

UK Free TV? ;) ;) ;)

Ha ! Please !

It's all a shambles quite honestly.

Totally agree - can you name any other country undergoing
digital switchover which has forced people to do more than
one retune?

No, I don't think I can ?



--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

Band pass filters -- what am I missing?
 

In message , Brian Gaff
wrote
This is what you get when a designer is not a person living in the real
world of the general public.

and a regulator that doesn't care about what the public may want.

--
Alan
news2009 {at} admac {dot} myzen {dot} co {dot} uk

Band pass filters -- what am I missing?
 

Mark Carver wrote:

Welcome to the world of high power overlapping DTT.

They give us all this bull**** about spectrum being scarce, but what
could be more profligate than transmitting DTT on ten times the
necessary power?

Bill

Band pass filters -- what am I missing?
 

Alan wrote:
In message , John
Rumm wrote

If the box supports manual scan... and of those that do, some have an
annoying habit of erasing all the stored channels each time you manual
scan. Hence you can only tune one mux.

And some boxes only add channels to the list when you scan so you first
have to reset to get rid of the previous scan information prior to new
scan.


Those little Philips boxes are very good. You can set the start and stop
scan channels or do the whole thing manually, and they display BER!

Bill

Band pass filters -- what am I missing?
 

Jim Lesurf wrote:
In article , Bill Wright
wrote:
Here's a list of bandpass filters.

http://dl.dropbox.com/u/11023364/bandpass%20filters.doc

Has anyone (independent of the makers) done measurements on them and put
the results onto the web?

Slainte,

Jim

I checked out most of the ones listed merely to ensure that they did
roughly what they're supposed to, which they all did. There were no big
surprises regarding through loss, out-of-desired-band attenuation, etc.
Of course this wasn't a rigorous test; just a 'fit for purpose' test.

Bill

Band pass filters -- what am I missing?
 

In message , Richard Tobin
wrote

There must be numerous ways that lists of channels for each
transmitter could be provided in a compatible way,

This is what I use on my Freeview box
http://www.admac.myzen.co.uk/mux_tuning/

--
Alan
news2009 {at} admac {dot} myzen {dot} co {dot} uk