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Author Topic: RFI and Spectrum cable DVR box  (Read 356 times)

W8BO

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RFI and Spectrum cable DVR box
« on: September 17, 2020, 07:58:38 AM »

Hello:

Sure this will stir things up a bit.

Recently back on air with a ground mount 6BTV with 40 radials.  Station is also properly grounded.  The ONLY PLACE I get RFI is the cable TV DVR / converter box from Spectrum

When I run more that 25 watts on usually 40M, but occasionally 30 & 20, the box goes into one of the menus as if a remote button was pressed.

Tried removing the batteries from the remote to confirm the RFI is not into the remote, but the converter box.  No TVs or any other device has this issue in the house.  No other TVs use a box from Spectrum.  All utilities are buried and the dmarc is on the opposite side of the building from the antenna.

I have put snap-on toroids on cables  and no help.  Outside of taking this crappy built box outside and shooting it, any ideas woudl be appreciated.

Thanks,

Phil W8BO
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W1VT

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Re: RFI and Spectrum cable DVR box
« Reply #1 on: September 17, 2020, 08:17:32 AM »

In order for snap on toroids to be effective at 40 meters, you typically need at least ten turns.  Or ten squared of them in series, or a hundred of them snapped on as the inductance varies as the square of the number of turns.

If the wires are thin you  can wrap all the wires through one large toroid.  This is typically more effective that separate toroids.

It is likely that either the cable TV RG-6 or the power cord/AC wiring is acting as antenna that picks up your signal.  It could be both.
I have a phone, now stored in the basement, that would pick up RFI via either the handset cord, the phone cord going out to the Power Pole, or the wall wart powering the device.
Which one it was varied with the band I was on.

Zak W1VT
« Last Edit: September 17, 2020, 08:20:33 AM by W1VT »
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W9IQ

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Re: RFI and Spectrum cable DVR box
« Reply #2 on: September 17, 2020, 09:02:45 AM »

Phil,

Are there any soft touch buttons on the box? These are very difficult to tame from an RFI perspective.

Also have the cable company check all of their coaxial connectors and their coax for a braid break. If the braid isn't properly crimped in the connector, RFI ingress is nearly ensured. As little as an ohm of braid to connector resistance can cause significant problems. They can often detect this by RFI egress from their cabling but that method is not foolproof due to the difference in frequencies.

You didn't mention the mix of the ferrite you are using on your snap-on toroids. Using the right mix is essential for any chance of success. Given the referenced bands, type 31 material is probably the best choice. Type 73 material may work better on 40 meters but it will not have as high of resistance on 30 and 20 meters.

Get large enough cores to experiment with the number of turns. Ideally, you want to maximize the resistance of the choke, not the inductance or capacitance. The reason for this is that inductance can actually make RFI worse depending upon the cable's common mode impedance. When you get to a certain number of turns, the choke's reactive impedance component switches from inductive to capacitive. This can also suddenly make the RFI worse. The resistive part of the choke's impedance, however, always reduces common mode current on the cable - the higher the resistance the greater the reduction of the common mode current. So experimentation with the number of turns is sometimes needed to find the "sweet spot" for your particular installation. Do this on all signal and power cables in and out of the box.

- Glenn W9IQ
« Last Edit: September 17, 2020, 09:17:59 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KF5LJW

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Re: RFI and Spectrum cable DVR box
« Reply #3 on: September 17, 2020, 09:06:23 AM »

Station is also properly grounded. 
If that were true, you would not likely have the problem, and what you describe is quite common among ham radio operators.

Your CATV coax shield, your radio coax shield, station ground, and AC service should use the exact same bonding point. Other wise you can have problems like RFI.

However I do not recommend you doing that because it it is simple, fast, and cost effective. Mostly because it is the very first place to start. It is not much fun if it works. Cost almost nothing, and takes almost no time to resolve. Hams like throwing a lot of money and time fixing problems they created :D
« Last Edit: September 17, 2020, 09:08:45 AM by KF5LJW »
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KC9NVP

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Re: RFI and Spectrum cable DVR box
« Reply #4 on: September 17, 2020, 09:29:26 AM »

I too have spectrum as my cable provider, but do not have issues running HF.  My issue is with 2 meter where stations assigned to ch 7 will freeze and go blank when ever I use my 2 meter radios even at 1/2 watt.  Good luck with your problem.
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AJ8MH

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Re: RFI and Spectrum cable DVR box
« Reply #5 on: September 17, 2020, 01:13:51 PM »

I also have a Charter DVR (Arris) along with a DVD player and low latency Bluetooth headphones.  My TV is a Samsung.  I feed the Samsung through an HDMI cable from the DVR. The Bluetooth headphone transmitter is connected to the Arris DVR through analog cables.  Analog cables also connect the DVD player to the TV.

I use a total of 8 cores with multiple turns through each except the two large cores snapped in series to the TV.  All wires running to the TV go through the large cores.  Multiple turns is out of the question unless I buy some REALLY BIG cores.

The TV is the only component affected by RFI.  I run 500 watts to two inverted-L antennas on 160, 80, 40 and 30.  The vertical section of each run up the side of my tower about 8 feet from the TV set.  Occasionally, I put the TV in some off-the-wall mode when the TV is OFF and I transmit on 40.  Once the TV is turned on, I have to dig deep into the menu to fix.  The Arris DVR is fine.

I actually replaced all TV cable coax and splitters when I moved in.  I have 5 TV's.  My tower and station ground is connected to the electric power/cable TV ground at the panel through a long run of copper and MULTIPLE ground rods.  The cable run to the affected TV is over 75 feet.

Dealing with RFI can be fun, but occasionally unproductive.

Search the Internet for "A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing" by Jim Brown, K9YC.  Good reading.
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W1NJC

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Re: RFI and Spectrum cable DVR box
« Reply #6 on: September 30, 2020, 02:01:44 PM »

If you rent the box, contact Spectrum and tell them the box is flaking out (don't tell them about the RFI) and demand a replacement new one.  You might get lucky and the new one will not have the problem. 

Otherwise yes, I see lots of winding cabling through ferrites in your future.  It might be interesting to disconnect cables one-by-one going into that thing and see if you can determine which I/O is the culprit (of course it could be multiple).  Don't forget about the power cable.

Good luck!

Nick
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WB4SPT

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Re: RFI and Spectrum cable DVR box
« Reply #7 on: October 02, 2020, 10:56:28 AM »

Station is also properly grounded. 
If that were true, you would not likely have the problem, and what you describe is quite common among ham radio operators.

Your CATV coax shield, your radio coax shield, station ground, and AC service should use the exact same bonding point. Other wise you can have problems like RFI.

However I do not recommend you doing that because it it is simple, fast, and cost effective. Mostly because it is the very first place to start. It is not much fun if it works. Cost almost nothing, and takes almost no time to resolve. Hams like throwing a lot of money and time fixing problems they created :D

A Faraday cage (ie: shield) has no need to be "bonded" to anything in order to work.  It works because the conductive sphere tends to prevent E-field production inside the shield. 
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N2KI

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Re: RFI and Spectrum cable DVR box
« Reply #8 on: November 30, 2020, 07:30:27 AM »

Phil,

I had the same problem with the new (plastic) Spectrum DVR box.  My issue was the box would reboot and go through some very strange gyrations on only 50 watts of key up, like it was possessed.  160M was the chief band that was an issue with 80 meters running in second.  The cure for me was to eliminate the cheap 12v DC power supply they provide with it.  I connected it to a 12vdc linear supply and the problem was solved. 
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KF7CG

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Re: RFI and Spectrum cable DVR box
« Reply #9 on: December 06, 2020, 04:29:28 PM »

Had a similar problem with one of my two Direct TV boxes. Both had touch controls, the old one was unquestionably stable; the new one acted as if possessed whenever I would get on. The was most true of 40 though it was troublesome on all HF bands. New box was cheap and dirty. Got rid of Direct TV and went to off the air reception. Problem solved.
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KL7CW

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Re: RFI and Spectrum cable DVR box
« Reply #10 on: December 07, 2020, 06:37:21 PM »

PHIL,
   It could be a defective cable or cable crimp to your TV box. Try another cable first. I had a situation here with RFI from various sources getting into my ham radios.  My antenna cables all ran through a rather expensive remote antenna switch just inside my house.  I discovered (with an ohmmeter) that one of the switch ports had a one ohm resistance in it's shield connection to the common port.  In my case, the problem was a poor switch design, but a small resistance (less than an ohm) in a crimp or coax will let RF in or out.  If I ran a KW the one ohm resistance could cause significant problems on TX.  I have found that if run roughly ten turns of coax through a type 31 core you will usually get at least 10 db of attenuation on many of the HF bands. Other core materials are better for various bands and the optimum number of turns depends upon the band.  If the problem is with the cables to the box and you can run 25 watts, 10 dB of attenuation should let you run 250 watts without problems.  I have used several chokes in series for more attenuation, or stacking cores may be better in some situations.  This is just one possibility, and other ideas such as ingress through the plastic box, etc. may be a more probable cause of your trouble.  It is good that you "thresh holed" the problem, so say a toroid fix let you run 80 watts.  You solved part of the problem, next you could try more cores, shielding, a new box, ingress through a power cable, etc.  Often there is more than one source of RFI to or from a device.  Many folks have more or better information.  I am not an expert, just an "old guy" who has been doing too much ham radio for 66 years !!                 Rick   KL7CW
             
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N5RMS

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Re: RFI and Spectrum cable DVR box
« Reply #11 on: January 07, 2021, 09:50:36 AM »

Just another old guy.  I had  RFI to my own OTA Tv when I removed my choke balun from my inverted L antenna.  Put the choke balun back on antenna feedline....no more RFI!
N5RMS
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