Signal too strong?

hobdell

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Just noticed I've got an in-line attenuator that must be relic left over from when my VM cable box was originally installed (its 3dB).

Has anyone had an issue with the signal strength being too strong?

If not I might as well remove it as I'm putting a splitter in for a new cable modem.
 

hobdell

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I've done a little bit more research on attenuators and a 3dB attenuator halves the signal strength. So, if I add another device on a splitter will it be required as i'm doubling the devices?

Thanks in advance.
 

slimshady

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truthfully i have found that these hardly do anything unless you go to the 50db attenuators which are good for disabling talkback
 

hobdell

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a 50dB attenuator should (if I've got the maths right) reduce the signal by to a 300th of the original signal strength. I'm suprised you get any signal through at all.

I guess the thing to do it to test the signal strength with and without the attenuator and with and without the extra device (cable modem) and see what the effects are.

Thanks for the reply Slim. :)
 

Tesla

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Does anyone know if the attenuators provide any kind of system network isolation?
 

hobdell

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Attenuators, from my very basic electronics, only decrease the signal strength. I have a 3dB attenuator in-line to my cable box and I'm getting SWR% of around 35 which makes sense.

As a rule of thumb:

3dB halves the signal.
6dB 1/4 the signal.
20dB 1/100 the signal. etc etc.

I don't know of any other characteristics other than signal reduction.

The only way I could see it providing any sort of network isolation is if it only worked one way like a diode. You have to send information both ways otherwise you'd never get an IP address though DHCP or any other kind of handshake.

All this is based on my dodgy electronics knowledge so please correct me if I'm wrong.
 

WIZARD22

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The reason why you will find a ATT pad on the feed is that the signal is fed to you a a higher level than what is required. The reason being that if a signal is fed at a higher level and there is any noise on the line it can be reduced to a level that will not affect the wanted signal, remember if you reduce the signal you will also reduce the noise floor and by transmitting at a higher level and reducing at local can give you a cleaner signal. this is a simple reason I can go more detailed if one wishes but as a general rule the noise is lower that the wanted signal but not always this is when you hav a real issue.
 

hobdell

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I get it thanks Wizard - by reducing the signal you reduce more noise to below the positive theshold.

So it reduces noise but doesn't provide any signal isolation.
 

Tesla

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The reason why you will find a ATT pad on the feed is that the signal is fed to you a a higher level than what is required. The reason being that if a signal is fed at a higher level and there is any noise on the line it can be reduced to a level that will not affect the wanted signal, remember if you reduce the signal you will also reduce the noise floor and by transmitting at a higher level and reducing at local can give you a cleaner signal. this is a simple reason I can go more detailed if one wishes but as a general rule the noise is lower that the wanted signal but not always this is when you hav a real issue.

Very good answer I agree that noise was a very big problem on analogue systems, does anyone remember the old dolby noise reduction system!!! Am I correct in thinking that most TV systems are moving over to digital which are not affected by noise like the analogue systems were?
 

Tesla

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Attenuators, from my very basic electronics, only decrease the signal strength. I have a 3dB attenuator in-line to my cable box and I'm getting SWR% of around 35 which makes sense.

As a rule of thumb:

3dB halves the signal.
6dB 1/4 the signal.
20dB 1/100 the signal. etc etc.

I don't know of any other characteristics other than signal reduction.

The only way I could see it providing any sort of network isolation is if it only worked one way like a diode. You have to send information both ways otherwise you'd never get an IP address though DHCP or any other kind of handshake.

All this is based on my dodgy electronics knowledge so please correct me if I'm wrong.

Another good answer, I remeber from my old TV days that they used to put a collection of capacitors on the RF signal just as it entered the TV for isolation, this was probably to shield the ariel system from mains volts. I wonder if there is any type of sytem isolation employed, we are all on very long piece of wire and you never know what people get up to on there systems behind closed doors!!!
 

hobdell

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Another good answer, I remeber from my old TV days that they used to put a collection of capacitors on the RF signal just as it entered the TV for isolation, this was probably to shield the ariel system from mains volts. I wonder if there is any type of sytem isolation employed, we are all on very long piece of wire and you never know what people get up to on there systems behind closed doors!!!

The problem with system isolation is that it has to be selective (like a firewall) as all communication is encapulated in comms protocols so a simple circuit couldn't do it. You couldn't just remove all signals over a certain level.

Any command sent to interegate your box by your supplier would be included in the other constant stream of packets and would need decoding before its characteristics could be determined. To do this in real-time would require some sort of processing. The only way your going to get this is via a bespoke IPS (Intrusion Prevention System) specifically designed for this purpose. Most of the shelf IPS's are IP network based but you'd need to be able to:

1) distinguish the characteristics of the interegating packets to filter them out.
2) Have some sort of ADC provider side conversion and DAC cable box (for digital/analogue conversion).
3) Physical layer conversion to/from ethernet-co-ax.

All this can be provided on your box if you know the answer to 1) with an integrated firewall. I think this the best bet rather than a bespoke device.
 
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