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

Here's a list of bandpass filters.

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

Bill

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 |
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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.

"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

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

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

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

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

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