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Need Rf Ground Breaker Design, CATV giving me 1.5v from coax

 
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gabito



Joined: 27 Jun 2008
Posts: 2

PostPosted: Fri Jun 27, 2008 6:30 pm    Post subject: Need Rf Ground Breaker Design, CATV giving me 1.5v from coax Reply with quote

Hi guys.. this is my first post here.

Sorry for my english. hope you can understand me.

BTW: I'm not a technician or anything.


I live in Argentina, where we still have analog CATV. The other day I measured the voltage that my cable company sends through the coax cable. To my suprise, it was 1.1v and sometimes fluctuating to 2.0v!

I guess I know now why a TV set of mine died on me last month.

Any how, I came up with a filter to get rid of the current and just let the RF signal through.

Here's my schematic:




Voltage is down to 0, of course due to the caps.

But something is wrong. We have approx 70 channels here, so:
1- channels from 2 to about 10 have very poor quality
2. channels from 20 to 30. poor.
3- 50 and up, poor.


I guess its the caps I'm using that is blocking or interfering with some of the frequencies.


Any suggestions guys?

Thanks!
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Mon Jun 30, 2008 3:03 am    Post subject: Re: Need Rf Ground Breaker Design, CATV giving me 1.5v from Reply with quote

gabito wrote:
Hi guys.. this is my first post here.

Sorry for my english. hope you can understand me.

BTW: I'm not a technician or anything.


I live in Argentina, where we still have analog CATV. The other day I measured the voltage that my cable company sends through the coax cable. To my suprise, it was 1.1v and sometimes fluctuating to 2.0v!

I guess I know now why a TV set of mine died on me last month.

Any how, I came up with a filter to get rid of the current and just let the RF signal through.

Here's my schematic:




Voltage is down to 0, of course due to the caps.

But something is wrong. We have approx 70 channels here, so:
1- channels from 2 to about 10 have very poor quality
2. channels from 20 to 30. poor.
3- 50 and up, poor.


I guess its the caps I'm using that is blocking or interfering with some of the frequencies.


Any suggestions guys?

Thanks!


That reading is very low & in no way will damage any equipment?
For one thing, stray readings on cable lines are common & will cause interference more than anything. If you are worried about blocking DC, your best bet is to use an adapter made for this purpose like;
http://tinyurl.com/65jytx
http://tinyurl.com/5q6trv
That schematic is not suitable for your application. While you are correct about the caps blocking DC, the addition of L1 & the 2 diodes(acting like capacitors in RF), you are attenuating the heck out of your signal by effectively making a bandpass filter.
The enclosure alone will also effect the signal & depending on your signal strenght, you are bound to degrade your signal regardless of the filter design.
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gabito



Joined: 27 Jun 2008
Posts: 2

PostPosted: Mon Jun 30, 2008 4:03 am    Post subject: Re: Need Rf Ground Breaker Design, CATV giving me 1.5v from Reply with quote

vtech wrote:


That reading is very low & in no way will damage any equipment?
For one thing, stray readings on cable lines are common & will cause interference more than anything. If you are worried about blocking DC, your best bet is to use an adapter made for this purpose like;
http://tinyurl.com/65jytx
http://tinyurl.com/5q6trv
That schematic is not suitable for your application. While you are correct about the caps blocking DC, the addition of L1 & the 2 diodes(acting like capacitors in RF), you are attenuating the heck out of your signal by effectively making a bandpass filter.
The enclosure alone will also effect the signal & depending on your signal strenght, you are bound to degrade your signal regardless of the filter design.




Thanks vtech..

I think I'll be getting one of those DC blockers for $1.99.

Do you think that one will work fine? The other site you gave me has blockers that go for about 25 bucks.
Since I'm no technician I have no idea what the real difference between them are.

What would you suggest?

I just need a dc blocker to get that 1-2 volt(s) out of the way and be able to watch channels 2 to 80.

Thanks!
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Mon Jun 30, 2008 5:46 am    Post subject: Reply with quote

Yes I noticed that too & quite honestly don't really know why is there such a difference?
Even though I have not used the $1.99 jobs, I don't see why spend any more than have to? ---still for the little~ 2volts, it is really not necessary.

You can always try it but, remember there is always a possibility that you may notice some signal degredation with any passive device inline especially if your signal level is marginal to start with.
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Mon Jun 30, 2008 8:05 am    Post subject: Reply with quote

The simplest way to achieve a such DC blocking would be to use an antenna connector with built-in blocking capacitors from any old tv with "live" chassis.
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power



Joined: 11 Jul 2008
Posts: 4

PostPosted: Fri Jul 11, 2008 9:34 am    Post subject: Re: Need Rf Ground Breaker Design, CATV giving me 1.5v from Reply with quote

Hello,

I was facing some problem with my TV. By visiting the links posted by you I have really got some help there.

Thanks for that.
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Fri Jul 11, 2008 6:07 pm    Post subject: Re: Need Rf Ground Breaker Design, CATV giving me 1.5v from Reply with quote

power wrote:
Hello,

I was facing some problem with my TV. By visiting the links posted by you I have really got some help there.

Thanks for that.


You are wlcome Very Happy
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ronwelldo



Joined: 01 Jan 2009
Posts: 1

PostPosted: Thu Jan 01, 2009 6:56 pm    Post subject: Ground breaker for CATV Reply with quote

Know this is a response to an old post but...Be sure you do not bypass a ground with a filter you would be asking for damaged equipment and most certainly a poor picture. Your best bet would be to make sure the CATV is bonded electricly to the power companys ground first off. This way you would not create a difference of potential ground in your home.
Since CATV signals cover a wide frequency range within the TV/Radio frequenct spectrum and are or should be EFI/RFI shielded and is sensitive to any characteristic impedance changes within the circuit, any filter that you could make would probably not pass muster. In fact,most of the commercially available inexpensive filters present problems as well.
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