T-8 Radio Interference

[Pappy]

I made an antennae from ribbon wire, tuned to the frequency of the oldies station in San Antonio. It was originally mounted outside on the south facia. The problem I had was the wind turning it in it's bracket.

When I rebuilt the roof of the playpen I made a bracket to hang it inside up from the joists. I could reach up with an old pool cue an turn it to improve reception on other stations. The metal roof didn't seem to affect it but the LiIon chargers did. When I added a T-8 light it went worse. There is nothing but static with the light on. I lowered the light and moved the antennae as high as I could. The chargers no longer cause interference, but the light still does. The T-12 lights I had before didn't cause any problems.

Any ideas or suggestions other than moving the antennae back outside, or switching back to T-12 lights? Any simple way to shield the antennae from the interference? Would changing the lead from the radio to the antennae to a coax cable do the trick?

[Slik Geek]

It is possible that the old T-12 light fixture had a magnetic ballast, so it operated at line frequency and was sine wave based, so it was reasonably "quiet" in an RF sense. The newer T-8 fixture likely has an electronic ballast, and it is switching at a much higher frequency, with square wave switching, which generates lots of harmonics and radio interfering RF noise.

Is the ballast marked as complying with FCC (it may say Part 18)? For residential applications, ballasts are required to meet it. Is the ballast well grounded? That may help. Adding ferrite beads to the power leads at the ballast may help as well.

How much distance between the ballast and the radio antenna?

[Pappy]

Problem Solved

The antenna is now mounted 20' high on the back wall of the playpen.

The antenna is made from ribbon wire based on this site http://www.kgnu.org/ht/helpfm.html#makeantenna and is tuned for the best reception on the weakest station I normally listen to. It is mounted on a piece of Maple.

The brackets are made from a Galvanized floor flange, a 12" length if Sch 40 PVC, and a 'T' fitting. The brackets are mounted one just above the top sill plate and one just below the ridge.



The mast is 1" aluminum tubing, courtesy of a customer that makes awnings, 14'9" long. A brass pin is inserted above the lower bracket. Once I determine the best orientation for the Austin and San Antonio stations, I will cut slots in the T for the pin to sit in.



Other than the slots, I need to drill holes for screws to secure the T's to the brackets. The antenna is connected to a converter and then to the radio with coax fed through the wall. I may add a wall plate and coax cable connector so the cable from the antenna to the wall and the inside cable are 2 pieces. I also need a cap piece on the wood mounting board to prevent warping.

[LCHIEN]

Pappy, if you are happy with your antenna then you don't need to do anything more.
FYI, i was confused when you called it ribbon cable, that's not what electrical engineers call ribbon cable, its twin-ax, or more specifically, 300- ohm twin ax.

you might improve things if you put a 300-to 75 ohm balun (like for TVs) just below the antenna lead out and convert to RG-59 coax for the long run down to your receiver. Typically a balun is about $1.50 and you can get the RG59 wire an the balun anywhere from radio shack to lowes or HD. this will reduce any interference being picked up by the twin ax leadin. Typically your receiver can be wired to receive either RG59 or twinax.

Better yet, you might just go get a directional FM-only antenna, if you are getting interference from other stations on that frequency.

The "folded dipole" antenna you made is insensitive from the ends of the arms, and most sensitive at right angles to the long arms. The sensitivity extends all the way to the sides, tops and bottom so it can pick up local interfereing signals like from your lamps. Its sensitivity pattern is like a big donut on edge with the arms going through the center.


A Properly made directional FM antenna will have a number of parallel arms in a plane. The sensitive direction will be in the plane of the arms and off one end of the array perpendicular to the arms. THe sensitivity in the opposite direction is usually intentionally reduced, giving the antenna a so-called front to back ratio. Also sensitivity form the top (outer space) and the bottom (your shop) will be significantly reduced. So the sensitivity pattern is like a long teardrop pointing out the end. This kind of antenna (called a Yagi) will have more sensitivity (e.g. pick up weaker signals) in the teardrop direction than the dipole antenna will in any of the donut directions. A quick look on the internet shows Yagis from Channelmaster, Weingard, and antennacraft starting around $24 and up. More bucks gets higher gain (more senssitive to weak signals) and higher front to back ratio (more rejection of signals and interference from the wrong directions) but even the cheapest will be better than a dipole in directionality.

[wardprobst]

Pappy,

Lchien has the right suggestions & theory. I would add that back in the 70s I worked at Radio Shack here in the Falls. Everyone wanted to pickup up stations in the Metroplex (120-150 miles southwest). I sold a lot of FM antenna setups. You've got the hard part done. If you mount a directional up there, you will be set. I used to have to sell a rotor with a setup to zero in on the signal as it wandered pretty widely in those days and I believe still does.

Good listening,
DP

[cabinetman]

Pappy - The floor flange you show as the base of the stand off...is it an electrical or plumbing flange? I need one with a 1 1/2" opening.

As for antennas, I use a simple FM dipole inside within 8' of T8's without interference. They are simple to move around...being flexible.
.

[Pappy]

C-Man, what you linked to is what I have, just cut to the length to best pick up a particular station. Still does fine across the rest of the band for stronger, closer stations. Not sure where the tower is for the station, but SA is 65 miles south of me.

The floor flange is from the plumbing dept. Not sure how big they carry at the box stores.

[Pappy]

C-man, I was in Lowe's and remembererd to look. They have the 1 1/2" flanges.

Loring, I have a balun installed with coax cable to the radio. Still get some static on the weak station with the light on so I will check into a Yagi.

[tseavoy]

When I was a radio ham in the 50s I always called it twin lead or maybe 300 ohm twin lead. A balun -- balanced to unbalanced, converts the twinlead signals (balanced) to coax (unbalanced), which is more impervious to interference at the cost of a slightly higher line loss. When TV first came to our area in upper Michigan we had a double stacked yagi using open wire twin lead to get reception from Duluth, 200 miles away. You got used to looking at a lot of snow.

Tom on Marrowstone

[Mr__Bill]

When TV first came to our area in upper Michigan we had a double stacked yagi using open wire twin lead to get reception from Duluth, 200 miles away. You got used to looking at a lot of snow.

Tom on Marrowstone

We had the same thing for northern Minnesota, the antenna was the size of a 2 car garage atop a long mast with a rotor. We had 2 Duluth channels and a Canadian channel from Winnipeg. Today we must have at least 75 on cable and really not much more to watch. Remember skip TV? Some nights it was from way down south.

Bill,
Ah, the good old days sure are better as a memory than they were at the time.

[Kristofor]

When TV first came to our area in upper Michigan we had a double stacked yagi using open wire twin lead to get reception from Duluth, 200 miles away. You got used to looking at a lot of snow.

On the TV or out the window both!

I live in a far southwestern suburb of the Twin Cities but I still receive a decent enough signal that a small indoor antenna works for digital tv, while several local AM radio stations are marginal.

We were camping up in Northern Minnesota a couple years ago and dialing around we managed to tune into the Twins. Not from a local affiliate that we were looking for, but from the station down in Tampa/St. Pete FL.

[cabinetman]

C-man, I was in Lowe's and remembererd to look. They have the 1 1/2" flanges.

Thanks for the info. I picked up one and an extender pipe. Made a base for my outdoor umbrella, using a 20" square Chattahoochee stepping stone (60 lbs) that I had.
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