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A and b group aerials to one decoder



 
 
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  #11  
Old April 1st 19, 11:21 PM posted to uk.tech.digital-tv
Ian Jackson[_7_]
external usenet poster
 
Posts: 239
Default A and b group aerials to one decoder

In message , Bill Wright
writes
On 01/04/2019 18:51, Terry Casey wrote:

An alternative is an A/B switch. These used to be widely used
by CATV subscribers in analogue days but not any more in the
UK.
Here's one:
https://www.ebay.co.uk/itm/2-WAY-A-B...oax-RF-Switch-
SPLITTER-Push-Button-Cable-TV-Satellite-Antenna/322799963868?
hash=item4b28608edc:g:SD4AAOSwiWlZ0iNF
or: https://tinyurl.com/y6kknxvd
Note that one input is marked CATV and the other ANT(enna) but
just ignore them and connect one aerial to each input.
I note the listing says only 4 available but the same item is
listed at similar prices from numerous Korean ebay vendors.
Unfortunately there is no specification available for these
switches, so it is not possible to ascertain the isolation
between inputs but, if it doesn't work as well as hoped for,
it's less than 6 so worth a punt.

In the analogue days these things were no good because of poor
isolation, which caused ghosting. But nowadays they might be OK.


Some of the 'proper' CATV A/B switches had an isolation of at least 80dB
at 900MHz - but they consisted of more than a simple slide switch. This
one (which does have some form of slide switch) only claims 70dB.
http://preview.tinyurl.com/yy2ntgph
This one claims 90dB:
http://preview.tinyurl.com/y2zvosph
--
Ian
  #12  
Old April 2nd 19, 04:12 AM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 3,382
Default A and b group aerials to one decoder

On 01/04/2019 23:21, Ian Jackson wrote:
In message , Bill Wright
writes
On 01/04/2019 18:51, Terry Casey wrote:

An alternative is an A/B switch. These used to be widely used
by CATV subscribers in analogue days but not any more in the
UK.
*Here's one:
*https://www.ebay.co.uk/itm/2-WAY-A-B...oax-RF-Switch-
SPLITTER-Push-Button-Cable-TV-Satellite-Antenna/322799963868?
hash=item4b28608edc:g:SD4AAOSwiWlZ0iNF
*or: https://tinyurl.com/y6kknxvd
*Note that one input is marked CATV and the other ANT(enna) but
just ignore them and connect one aerial to each input.
*I note the listing says only 4 available but the same item is
listed at similar prices from numerous Korean ebay vendors.
*Unfortunately there is no specification available for these
switches, so it is not possible to ascertain the isolation
between inputs but, if it doesn't work as well as hoped for,
it's less than £6 so worth a punt.

In the analogue days these things were no good because of poor
isolation, which caused ghosting. But nowadays they might be OK.


Some of the 'proper' CATV A/B switches had an isolation of at least 80dB
at 900MHz - but they consisted of more than a simple slide switch. This
one (which does have some form of slide switch) only claims 70dB.
http://preview.tinyurl.com/yy2ntgph
This one claims 90dB:
http://preview.tinyurl.com/y2zvosph


I used to use some that actually shorted out the unwanted input. They
were 50ohm but they worked OK on 75ohm.

Bill
  #13  
Old April 2nd 19, 08:09 AM posted to uk.tech.digital-tv
Ian Jackson[_7_]
external usenet poster
 
Posts: 239
Default A and b group aerials to one decoder

In message , Bill Wright
writes
On 01/04/2019 23:21, Ian Jackson wrote:
In message , Bill Wright
writes
On 01/04/2019 18:51, Terry Casey wrote:

An alternative is an A/B switch. These used to be widely used
by CATV subscribers in analogue days but not any more in the
UK.
*Here's one:
*https://www.ebay.co.uk/itm/2-WAY-A-B...oax-RF-Switch-
SPLITTER-Push-Button-Cable-TV-Satellite-Antenna/322799963868?
hash=item4b28608edc:g:SD4AAOSwiWlZ0iNF
*or: https://tinyurl.com/y6kknxvd
*Note that one input is marked CATV and the other ANT(enna) but
just ignore them and connect one aerial to each input.
*I note the listing says only 4 available but the same item is
listed at similar prices from numerous Korean ebay vendors.
*Unfortunately there is no specification available for these
switches, so it is not possible to ascertain the isolation
between inputs but, if it doesn't work as well as hoped for,
it's less than 6 so worth a punt.

In the analogue days these things were no good because of poor
isolation, which caused ghosting. But nowadays they might be OK.

Some of the 'proper' CATV A/B switches had an isolation of at least
80dB at 900MHz - but they consisted of more than a simple slide
switch. This one (which does have some form of slide switch) only
claims 70dB.
http://preview.tinyurl.com/yy2ntgph
This one claims 90dB:
http://preview.tinyurl.com/y2zvosph


I used to use some that actually shorted out the unwanted input. They
were 50ohm but they worked OK on 75ohm.


I've got a couple of a later type of Jerrold switch. It's about 3"
rectangular diecasting, 3/4" thick, in which are matched 75 ohm
trough-lines. These provide a high degree of screening. The switch is a
sort-of rotating capstan affair, and the wanted inputs get terminated in
75 ohms. I recall measuring the isolation at about 90dB around 900MHz.
--
Ian
  #14  
Old April 2nd 19, 06:07 PM posted to uk.tech.digital-tv
[email protected]
external usenet poster
 
Posts: 79
Default A and b group aerials to one decoder

Or use a televes Avant or a Johansson superprofiler....

The latter is available brand new at 300 quid and you can map input muxes to different output frequencies if you need to make room for other stuff.....
 




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