Question: Found an antenna in the attic, modified to work with FM. Thoughts?

jakel01

DTVUSA Jr. Member
#1
First post here FYI.

I've had an old antenna in the attic for years that went unused. The elements were about 44 inches before I trimmed them to the upper, middle, and lower 5/8 wavelengths of the FM band. I placed it in the attic, positioning it nominally along the horizontal plane. Problem is, the main stations that transmit are at 68 degrees, and I receive them fine, but a station at about 115 degrees doesn't come in at all, even though its the same miles away.

Is there a better configuration that would make this antenna less directional? Would I need two antennas pointing about 45 degrees from each other? The stations are about 45 miles from my location.
ANY help would be great, I apologize if this question was asked and replied to a few pages back, I did not do any searching or looking.
 

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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#3
Jake,

The link to your FM survey was the starting page and not the result of the survey. Please try again. Is your antenna a 'Discone' variation? I ask because it is similar to VHF Police Scanner antennas from 30 years ago.
Jim
 

jakel01

DTVUSA Jr. Member
#4
Jake,

The link to your FM survey was the starting page and not the result of the survey. Please try again. Is your antenna a 'Discone' variation? I ask because it is similar to VHF Police Scanner antennas from 30 years ago.
Jim
View attachment 3438
As for the type of antenna, I have not a clue what it's original purpose was. It was in the attic and had 300 ohm wire that terminated somewhere in the wall.
 

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#5
Links to FM Fool reports do not work. I've tried that before. The attached image is too small to read.
It looks as if you have tried to construct a bow tie type antenna for the FM band. A broad band width bow tie type antenna built for FM broadcast band will be quite large, and needs to be about one wave length wide to produce gain over a simple smaller dipole or loop. It looks as if you have cut three elements to 5/8 wave length for three frequencies across the FM band. The elements will interact lowering the resonant frequency of the whole antenna.
While I don't know how you are feeding the antenna I would suggest using a 75 to 300 ohm balun if your using coax.
You could try adding a reflector.
If I needed to build a simple antenna for the FM broadcast band my choice would be a full wave loop.
http://www.wryr.org/Antenna_instructions.pdf
 G1VVP - Skegness DX: The (In)Famous Faulkner FM Loop Antenna!
Steve
 

jakel01

DTVUSA Jr. Member
#7
Thanks for the insight. I was using the bowtie with a 300 to 75 balun.

As for the link to TV fool, pretty much all stations are edge 1 or edge 2, with the bulk of stations at 67 degrees, which I have no trouble picking up, but the one station at 99 degrees is the stinker that I can't pick up reliably. My car has no issue picking up all stations while parked in the driveway.

Other things I have tried...
The classic folded dipole that comes with stereos mounted to the attic rafters with a balun, but no luck getting all stations.
Also made a rubber duck whip that plugged right into the back of the stereo, actually worked the best of all my attempts, but only way I could get my station at 99 degrees to come in was with standing just right, and at best it was still static-y.

I have a compression fitting tool, I redid all my old crappy crimp on connectors with compression, and replaced any suspect RG6 with new cable.

Still confused as to why my home stereos have trouble, yet my casio alarm clock, and a Tivoli Audio Model One using the internal antenna have no issue getting stations to come in.

At least all this gives me something fun to do, harnessing the magic of RF is always fun and rewarding.

Also edited an above post to show proper graph from FM fool
 
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#8
Jake
Thank you for the pleasant response. I'm a seat of my my pants antenna builder myself, but I do study the works of others who are much more knowledgeable then myself.
I'll try to offer some ideas to think about.
FM broadcast signals are circular polarized. Meaning that the transmit both a vertical and horizontal signal. In a perfect world both should be equal in strength.
http://www.dtvusaforum.com/dtv-hdtv...sion/6472-fm-antenna-polarization-choose.html
Even from the transmit antenna both polarities are often not equal, and then when terrain in between gets involved things can really change as to which polarity is received best.
A full wave loop fed from the bottom center is horizontally polarized. When fed at the center of a side it is vertically polarized. This applies to both round, and square loops.
A dipole has a gain of 2.15 dBi. The gain of a full wave loop is about 3 dBi. An insignificant improvement over a dipole in most situations. In the real world I like loops.
A correctly built Bow tie antenna will have about 4 dBi gain. A bow tie antenna built for FM broadcast band will be about 128 inches wide, 64 inches per side. One wave length.
You really don't need to try and channel cut an FM receiver antenna. It should be simple enough to build an antenna fed into 300 ohm with an swr below 3 to 1 across the FM band. You are not trying to load a kilowatt into it.
The simplest way I know of to get 3 db more gain is to add a reflector. keep in mind a reflector needs to be over 1/2 wave length long.
When I've found myself in need of an FM broadcast antenna I've just done a little bit of simple seat of my pant work.
1005/88=11.42x12=137.04/4=34.26. About 137 inches of 12 or 14 awg wire 34.25 inches per side. Crude but did the job for what I wanted at the time.
The accuracy of the 1005/f loop formula is very questionable, and controversial at this point in time. It works for small wire antennas.
While I've never had need to build an FM broadcast antenna with much gain I'd suggest trying a loop with reflector.
Here are some ideas keep in mind they must be rescaled to the FM band. Much larger.
Hi-VHF Circular Loop + Reflector
Hi-VHF Square Loop + Reflector
How to rescale is covered in the third paragraph of the home page.
Albums By holl_ands - ImageEvent
If you need more gain spend some time on this site. He has some good FM yagi plans.
88–108 MHz
I don't have the answers. I just thought I'd send a few ideas to look at.
I'm not certain why you have trouble with just one receiver.
Steve
 

jakel01

DTVUSA Jr. Member
#9
Tried a few more things today.
I built a square loop, with some 1x2 scrap wood, and made the lengths to 32" with hopes to catch the 89.3 station. No luck on the home receiver. SO strange! Henry Kloss radio picks up stations just being near the loop, doesn't even have to be connected to it!

I did discover some of my coax in the wall had been nibbled on by mice, so I thought to try bypassing all of it and running a line straight from my ground block outside where the DTV antenna connects right to my home receiver with a cable run thru a window. No stations come in under 100 MHz... WHAT? Almost all the TV and FM stations are transmitted from 3 towers the DTV antenna is aimed at.

BUT, if I plug in the rooftop DTV antenna directly into my Henry Kloss One radio, I get all stations clear as day, even stations behind and off angle.
The DTV antenna is this style hdtv_a8.jpg

Basically ANY antenna other than what it came with (the crappy 6' wire with a slip on plug) doesn't work on the home receiver.

Time to see if whiskey helps reception and brainstorming.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#10
Jake,

Have you tried splitting the signals from your rooftop antenna between your TV's and FM Stereo ... thus, adding your FM receiver to your system as if it was an additional TV set?

Jim
 

jakel01

DTVUSA Jr. Member
#11
I have tried splitting the signal from the DTV antenna and haven't had much luck getting good signal.

Tonight I prototyped a folded dipole from 1/2 copper and I'm having GREAT results so far. I have yet to solder it, but I can get all stations on the home receiver in clear stereo. Tomorrow I'm going to strap it to a PVC pole and see what rooftop results I can achieve.

Loop of fail next to the dipole of success

 
#13
Good to hear of your success. The folded dipole looks good to me. The one thing I want to mention is a loop fed on the top or bottom will be horizontally polarized, and when fed on the side will be vertically polarized. While I've always used horizontally polarized antennas for FM. Since FM signals are circularly polarized use what works best at your location.
Steve
 
#15
I was referring to home built loops, and simple dipoles I have used on home receivers. Car radios are the reason FM broadcast went to circular polarization. With circular polarization you waste half your power on the wrong polarization. Ideally one would want to use a circularly polarize receive antenna for FM broadcast. I really have not found the time to get too far into building better FM radio antennas. I was always happy with the stations I did receive some reliably from over 100 miles. Too many antennas, too many frequencies, not enough time, money, or other resources to do it all in one lifetime.
Steve
 
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