LOW PASS filters -who makes them and who has schematics?
Curtis Scholl
I think I may need a LOW PASS filter to keep my emissions from
interfering with the TV next door.
Here is the situation from the evidence presented so far.
Last week I had a multiband (multi dipole) inverted antenna up about
16 feet. It started looking very ugly so I built a multiband (three
different quarter wave) vertical. Last week I received no complaints.
This week I am told that my antenna is radiating into her TV. She hears
my call sign on the unit with a fancy cable box in the living room. She
does not hear me on the non cabled TV in the back room. Yesterday she
did not hear me either and the verticals did not have a "counterpoise".
This morning I ran some 10/15 foot wires from the central ground
point of the antenna out to a distance of 10 feet give or take to make a
"ground plane". Now she hears something in the cable box.
Is there enough evidence here to suggest that the cable for the TV
set is underneath my counterpoise? Or is the power line being invaded by
my signal? If it were the power lines being polluted, would not the
older TV in the back room be affected?
Would a LOW PASS filter that would allow nothing above 30 MHz to
pass be sufficient or would anyone suggest moving the ground wires
around?
Curtis Scholl
KG8SU
Gary Coffman
> Would a LOW PASS filter that would allow nothing above 30 MHz to
>pass be sufficient or would anyone suggest moving the ground wires
>around?
I'm doubtful that a low pass filter on your transmitter will do any good.
This sounds like typical fundamental overload to me. If you were radiating
harmonics, they would show up on specific frequencies, and would move
as you tuned to different frequencies. That doesn't sound like what's
happening. The fact that the over the air TV is unaffected reinforces
this conclusion.
You're just coupling enough amateur frequency signal into her cable box
to cause this symptom. What you need to figure out now is how it is
getting in, and how to stop it. (Actually, it isn't legally your problem. It
is the cable company and your neighbor's problem. But trying to be
helpful in solving the problem is a good neighbor policy.)
The signal could be getting into the cable box either via common mode
on the cable or via the power line. Since the problem didn't exist when
you were running a horizontal antenna, but does now that you're running
a vertical, you need to look around and see how the relationship between
your antenna patterns and the cable and power lines have changed. It
is likely that you now have a current loop paralleling one or the other
now when you didn't before.
Unless you want to change your antenna system again, you can try
ferrite filters on the power cord and cable at the offending cable box.
(Providing the neighbor will let you do that.) There's no filter you can
add to your transmitter which will help.
Gary
Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
Dale Parfitt
Curtis Scholl wrote:
> Hi Group!
>
> I think I may need a LOW PASS filter to keep my emissions from
> interfering with the TV next door.
> Here is the situation from the evidence presented so far.
>
> Last week I had a multiband (multi dipole) inverted antenna up about
> 16 feet. It started looking very ugly so I built a multiband (three
> different quarter wave) vertical. Last week I received no complaints.
> This week I am told that my antenna is radiating into her TV. She hears
> my call sign on the unit with a fancy cable box in the living room. She
> does not hear me on the non cabled TV in the back room. Yesterday she
> did not hear me either and the verticals did not have a "counterpoise".
>
> This morning I ran some 10/15 foot wires from the central ground
> point of the antenna out to a distance of 10 feet give or take to make a
> "ground plane". Now she hears something in the cable box.
>
> Is there enough evidence here to suggest that the cable for the TV
> set is underneath my counterpoise? Or is the power line being invaded by
> my signal? If it were the power lines being polluted, would not the
> older TV in the back room be affected?
>
> Would a LOW PASS filter that would allow nothing above 30 MHz to
> pass be sufficient or would anyone suggest moving the ground wires
> around?
>
> Curtis Scholl
> KG8SU
I sincerely doubt your problem is harmonic radiation- this being the ONLY
problem that an LPF would solve. Sounds more like fundamental overload of
the TV ( HPF) or common mode (ferrite chokes).
Dale W4OP
Cortland Richmond
However, I'd say your neighbor will need to install an AC power filter. She
may need to filter not just the cable box, but also devices hooked up to it.
Cortland
David Rich
speakers on my television, hi-fi vcr, stereo with surround combination if I have
the dolby surround "ON". The television receives it signal from a yagi on the
roof. I use a R7 vertical not too far away. The interfering sound is not to
loud and goes away when I turn the Dolby surround "OFF". My transmitter does
interfere with the television picture a little mostly when I am on 20 meters
phone and the television is on channel 4. I have tried Radio Shack and
Vectronics HP filters on the TV and VCR and wrapping the speaker wires with
ferrite but it does not seem to really help. The Vectronics has both a HP
filter and ferrite core for common mode. It is not that bad of interference but
I would like to get rid of it. Do you think wrapping the AC cord with a ferrite
filter would help? I am only concerned about the sound interference. I guess I
could try the old LC 100 uH choke and .001 uF shunt cap on the speaker side
trick. I hate to go through all that work to see that it does not help one bit.
Since my shack is in the basement I use a cold water pipe for ground. I have a
ground rod next to the R7's antenna mast. I strap the ground rod to the cold
water pipe also. I also have a Alpha Delta Transi-Trap lightning protection
device in-line with the HF cable. The lightning protection device is strapped
to the cold
water pipe as well.
73 Dave KG0US
Paul Keinanen
wrote:
>This week I am told that my antenna is radiating into her TV. She hears
>my call sign on the unit with a fancy cable box in the living room. She
>does not hear me on the non cabled TV in the back room. Yesterday she
Did this happen on all TV channels ? Was the picture affected ?
If the picture is not affected and the problem occurs on all channels,
then this is an audio break through directly into the audio system of
the TV.
Are there external speakers connected to the TV ? If so, disconnect
the external speaker wires from the TV and the interference is not
heard on the internal speaker, the problem is audio break through from
the speaker cables. If there are no external speakers, then most
likely, the interference comes through the power line and wrapping the
power cord around a ferrite bar should reduce that interference.
Paul OH3LWR
Clifton T. Sharp Jr.
> A properly operating cable system would not pick up radiated signals.
Then again, a properly operating cable system would be an anomaly.
(Who, me? Cynical? Angry because the local leaky cable system spent years
with Discovery Channel, my landlord's favorite, on 144-150 MHz? Nawwww.)
--
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Al, N2NKB
transmissions. Three times he has had the cable company come over to is house to "fix" his problem. He also
mentions that one of the cable station's audio is at the same frequency as the air distress band.
Al
Gary Coffman wrote in message ...
>On Sun, 16 Jan 2000 16:56:52 -0500, Curtis Scholl <csc...@izzy.net> wrote:
>> Would a LOW PASS filter that would allow nothing above 30 MHz to
>>pass be sufficient or would anyone suggest moving the ground wires
>>around?
>