simple explanation please

jacko

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#1
could somebody explain to me please the differences
between a televes notch filter,attenuator and line amplifier.
take it easy please,just learning.
thanks in advance.
 

PaulR

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#2
Not just for Televes, they are just one manufacturer of aerial related items.

A notch filter will allow most radio signal through but severely attenuate (weaken) frequencies for a very narrow band - usually enough for 1 channel to be "notched" out. Similar products are low pass filters (all below a certain frequency), high pass filter (guess!) and band pass filters (a range of channels allowed through, like a wide notch filter in reverse).

An attenuator reduces the level of a signal (radio in this context). Sometimes a signal is so strong that it causes problems for a receiver by overloading the front end (first bit of the receiver). This can cause interference problems with your desired signal. Reducing the signal strength, sometimes of the desired signal as well, can allow the desired signal to get through without distortion.

A line amplifier boosts the strength of a radio signal to overcome losses in the connecting cable. They also boost the noise in the signal and introduce a certain amount noise of their own so should be used with extreme caution. They are usually NOT the answer to problem.

PaulR
 

jacko

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#3
very well explained,
thanks Paulr.
do you think a notch filter would cure my problem of a fluctuating digital
signal,coming across the sea from a transmitter 23 miles away.
(i live in tenerife).the signal quality and stength are normally quite
high,but occasionally drops off to 10 per cent.using televes dat 45 aerial.
thanks once again.
 

PaulR

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#4
Unless you have a strong local signal which is interfering in some way - no. If there is a strong transmitter locally then you could try to notch out the channels but this could be difficult/expensive if there are multiple channels causing the problem.

Signals across the sea are subject to fading so I would think you would be best looking at getting a much more sensitive and directional aerial and change your downlead cable to a low-loss satellite type (CT100 or similar in the UK).

PaulR
 

PaulR

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#5
Just found your previous post on the subject. You've already gone through a lot of the steps already.

Did you find out whether there are any local transmitters which could be affecting your signal?

Can you raise the hieght of your aerial?

Is your cable run as short as possible? Is it an unbroken run of cable?

Changing the aerial might help. Something like the DAT 75 would pull in a bit more signal and, as a bonus, be more selective where the the signal comes from.

PaulR

Have you been able to find out what the "filter" was that your friend had fitted?
 

jacko

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#6
thanks for the reply PaulR.
i will try adjusting the height of the aerial first. cable run is 6 metres.the sat cable
is in 2 parts connected with sat in line screw connectors,think i¨ll change the cable
so that there are no breaks.taking my mates filter to the sat shop on friday. i think the aerial should be ok as some days the signal is 90 per cent and quality 100 per cent.
the aerial consists of 3 arms which are spaced apart to make it wideband i presume,
maybe if i take the plastic spacer off and bring the 3 arms together so that they are parallel to each other,making it more directional.
well i¨ve got a couple of things i can try now,thanks once again for the advice.
ps:don¨t know of any local transmitters.
 

rolfw

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#7
Don't adjust the geometry of the antenna, they spent a lot of time getting it that way. :) Do not confuse wideband with a wider reception angle.

There are of course much higher gain antennae around, Televes do one, similar in appearance to the DAT45, but longeeeeeeer.
 

PaulR

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#9
The DAT75 is the longer version of the DAT45.

BTW, what aerial does your friend have?

PaulR
 

jacko

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#10
hi PaulR,
my mate has a 28 element logorithmic aerial but had the exact problems
as me ,with the occasional drop off in signal.originaly tried to get one of
these aerials but couldn¨t find one here in tenerife.
have been on the televes site and have found out that the dat 45 is fitted
with a MRD margin raising device,which amplifies the signal as well (13db).but apparently
this doesn¨t work unless you buy a 5020 12/24v power supply and connect it
between aerial and receiver.
well another thing to try.hopefully have it resolved soon.
 
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