FM radio antenna

FM does it with frequency!
Bonaro
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FM radio antenna

Post by Bonaro » Sat Dec 10, 2016 1:45 am

I want to improve the FM radio reception in my garage/man cave. I want to build a indoor or outdoor antenna. I have been googling around for some antenna plans and found many but I dont know which one to build. I am pretty handy about most things but I am just learning about antennas/eletronics.

Can you guys link me to some plans I can buld?

TPT
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Re: FM radio antenna

Post by TPT » Sat Dec 10, 2016 8:11 am

A quick google:

https://archive.org/details/VhfHandbook

Various amateur publications give you formulae to design antennas for 6 and 2 meters---which straddle the FM band. You can adjust these formulas for FM frequencies & build some interesting antennas out of copper water pipe. My friend Bob built a folded dipole out of pipe for an FM translator for our FM station that worked for years before we replaced it with a commercial circularly polarized antenna.

All depends on what you need--a highly directional antenna to pick up a weak station, or an omni-directional antenna to get more signal into your FM radio.

Bonaro
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Re: FM radio antenna

Post by Bonaro » Sat Dec 10, 2016 5:15 pm

I will explain my situation and maybe you can make a suggestion.

I live in the foothills of south Puget Sound and I'm trying to tune to stations only in Seattle, about 50 miles away. I have near line of sight with only a couple low hills between us. I also have 750Kva power transmission lines in the line of sight and only about 300' away. Currently I only have a 20' piece of wire stapled to the rafters for an antenna and I get ok reception. Somethings the strength is low and the background hiss is high and i need to cancel stereo to make it better.

It would seem a directional antenna would work for me. Would making it larger be better?
I have read that adding an amp would amplify the noise as well so I am looking at a better antenna first.

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Shane
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Re: FM radio antenna

Post by Shane » Sat Dec 10, 2016 7:27 pm

Sounds like a job for a Yagi antenna. Hit the books!
Mike Shane, CBRE
---Omaha---

Bonaro
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Re: FM radio antenna

Post by Bonaro » Sun Dec 11, 2016 12:50 am

I have seen plans for a Yagi antenna and I can build this. I have aluminum tube and lots of copper wire laying about

Will it work better if I make it bigger?...tips?

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kkiddkkidd
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Re: FM radio antenna

Post by kkiddkkidd » Sun Dec 11, 2016 7:47 am

Bonaro wrote:I have seen plans for a Yagi antenna and I can build this. I have aluminum tube and lots of copper wire laying about

Will it work better if I make it bigger?...tips?
More elements = more gain and higher directivity.

If you get decent reception with a simple wire in the attic, a 3 or 4 element yagi mounted outside will probably be plenty get full quieting. On the other hand, a simple, cheap, omni loop may be all you need at 50 miles for Class C stations.

A yagi such as"
http://www.mcmelectronics.com/product/S ... 0-/30-2460

Omni Similar to :
http://www.solidsignal.com/pview.asp?p= ... ce=inhouse
or
http://www.mcmelectronics.com/product/3 ... oCHEXw_wcB

The hardest part of building a yagi is the "driven" element and matching hardware. The other elements can be grounded or floating.

Most VHF TV antenna's cover the FM band as well.

Building antenna's has long been my favorite aspect of ham radio but lately don't seem to have time to do so.

Regards,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

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Deep Thought
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Re: FM radio antenna

Post by Deep Thought » Sun Dec 11, 2016 11:56 am

Currently I only have a 20' piece of wire stapled to the rafters
How are you "feeding" this? Off the end or from the middle as a sort-of "T" antenna? 20 feet may be too long for either of those.

One of the best shorter-range antennas is the simple twinlead folded dipole that used to come with every stereo receiver. They are only about six feet end to end. Most receivers these days use 75 ohm F connectors so you'd have to find a matching transformer to go from the 300 ohm leads to the 75 ohm input.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

TPT
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Re: FM radio antenna

Post by TPT » Sun Dec 11, 2016 1:00 pm

If you enjoy the challenge a Yagi would be your best bet. As noted, the problem is matching the "driven" element, that is, the element connected to the radio. On a Yagi, the remaining elements act to concentrate the received signal into the single element used for reception. Some designs use a folded dipole (think of a paperclip with parts missing) that is often 300 ohms. You would want to convert this to 75 ohms to feed a coaxial cable (and cut down electrical noise pick-up) into the radio. Luckily 300 ohm to 75 ohm matching transformers are cheap & available on Amazon.

Of course--if you would rather play the radio rather than play with an antenna, a good all-band TV antenna would work fine. Like this one from Lowes:
https://www.lowes.com/pd/RCA-Outdoor-Di ... na/3548988.

Just watch out for the "HDTV" antennas, they are mostly UHF only antennas, not much use for the FM band. And in dry weather, that high voltage line will still get you, no matter how much gain you have.

Bonaro
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Re: FM radio antenna

Post by Bonaro » Sun Dec 11, 2016 2:51 pm

kkiddkkidd wrote:
Bonaro wrote: If you get decent reception with a simple wire in the attic, a 3 or 4 element yagi mounted outside will probably be plenty get full quieting. On the other hand, a simple, cheap, omni loop may be all you need at 50 miles for Class C stations.

A yagi such as"
http://www.mcmelectronics.com/product/S ... 0-/30-2460

Omni Similar to :
http://www.solidsignal.com/pview.asp?p= ... ce=inhouse
or
http://www.mcmelectronics.com/product/3 ... oCHEXw_wcB

The hardest part of building a yagi is the "driven" element and matching hardware. The other elements can be grounded or floating.

Most VHF TV antenna's cover the FM band as well.

Building antenna's has long been my favorite aspect of ham radio but lately don't seem to have time to do so.

Regards,
Excellent info, guys. Thank you.
As I said I am not a electronics guy so learning this via Google is pretty confusing.

On a Yagi - the plans I have seen show a specific diameter for the element rods, usually small like 3/8". I have a pile of 1" aluminum tube. Can this be used instead of the smaller?

I see a "gain rating" on many of the antennas. Is the gain of an antenna proportionate to its ability to provide a better signal?

The omni is interesting because it will fit in the attic. I presume the diameter is important but what if I wrapped copper wire around a barrel of the right diameter? Would it be an improvement to stack 2 or 3 of these?

Bonaro
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Re: FM radio antenna

Post by Bonaro » Sun Dec 11, 2016 2:55 pm

Deep Thought wrote:
Currently I only have a 20' piece of wire stapled to the rafters
How are you "feeding" this? Off the end or from the middle as a sort-of "T" antenna? 20 feet may be too long for either of those.

One of the best shorter-range antennas is the simple twinlead folded dipole that used to come with every stereo receiver. They are only about six feet end to end. Most receivers these days use 75 ohm F connectors so you'd have to find a matching transformer to go from the 300 ohm leads to the 75 ohm input.

The antenna I am using is just a chunk of speaker wire strung thru the rafters in no particular direction. When I built the garage I just wanted some radio and threw this up...now 10 years later.... :roll:

Bonaro
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Re: FM radio antenna

Post by Bonaro » Sun Dec 11, 2016 3:04 pm

TPT wrote:If you enjoy the challenge a Yagi would be your best bet. As noted, the problem is matching the "driven" element, that is, the element connected to the radio. On a Yagi, the remaining elements act to concentrate the received signal into the single element used for reception. Some designs use a folded dipole (think of a paperclip with parts missing) that is often 300 ohms. You would want to convert this to 75 ohms to feed a coaxial cable (and cut down electrical noise pick-up) into the radio. Luckily 300 ohm to 75 ohm matching transformers are cheap & available on Amazon.

Of course--if you would rather play the radio rather than play with an antenna, a good all-band TV antenna would work fine. Like this one from Lowes:
https://www.lowes.com/pd/RCA-Outdoor-Di ... na/3548988.

Just watch out for the "HDTV" antennas, they are mostly UHF only antennas, not much use for the FM band. And in dry weather, that high voltage line will still get you, no matter how much gain you have.
Living near transmission lines can be interesting and I could tell a few stories but I will save that for a different thread.
There is a huge amount of energy being thrown off these lines. When it's cold and wet outside I can stand under them and hold a 4' fluorescent tube over my head and it will light bright enough to read by. I have played around with capturing this power and it doesn't behave...not easy to play with. :wink:
I know it must wreak havoc on radio reception but it seems to be pretty constant. I dont see a decrease in reception or more static when the weather changes and when the weather is very cold (high demand) those lines really hum.

The one at Lowes looks great but I would rather build an antenna and save the $

ChuckG
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Re: FM radio antenna

Post by ChuckG » Sun Dec 11, 2016 9:32 pm

Bonaro wrote: On a Yagi - the plans I have seen show a specific diameter for the element rods, usually small like 3/8". I have a pile of 1" aluminum tube. Can this be used instead of the smaller?
Yes, but the fatter tube is electrically shorter, requiring the lengths of the elements be changed. The math to figure that out is probably available online somewhere.
I see a "gain rating" on many of the antennas. Is the gain of an antenna proportionate to its ability to provide a better signal?
Yes. The higher the gain, the more output the antenna provides.
The omni is interesting because it will fit in the attic. I presume the diameter is important but what if I wrapped copper wire around a barrel of the right diameter? Would it be an improvement to stack 2 or 3 of these?
Look closely at the MCM (stellar labs) link. That's still that same basic twin-lead folded dipole antenna, the kind most receivers are sold with, only formed into a circle. Diagram below.
Yes you can stack elements to increase gain, but keep in mind that 1/2 wave spacing is about 5 feet, so a vertical stack gets out of hand rather quickly. A Yagi will get you the same or better gain in less space, provided you don't need the omnidirectional pattern.
figure2.gif
figure2.gif (26.31 KiB) Viewed 567 times
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Chuck Gennaro
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KPJL FM
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Re: FM radio antenna

Post by KPJL FM » Mon Dec 12, 2016 8:30 am

Bonaro wrote:
The antenna I am using is just a chunk of speaker wire strung thru the rafters in no particular direction. When I built the garage I just wanted some radio and threw this up...now 10 years later.... :roll:
Ha, sounds like you have the makings of a radio engineer.
Trim to fit, paint to match, tune for minimum smoke.

Bonaro
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Re: FM radio antenna

Post by Bonaro » Wed Dec 14, 2016 12:05 am

I am going to try to build a yagi. The two stations I always listen to have their repeaters in the same hilltop and I really don't tune to any other stations so a yagi will work great.

I found a calculator online that will tell me the length of the director elements and spacing.
I have 1" aluminum tube to use for the main beam and some old aluminum arrows to use for the director elements.

Some questions:
The reflector element on the back. I have seen designs that have a single rod, several vertically stacked rods, wire mesh and a aluminum plate. Since this is passive does this matter what its made from so long as it reflects? I have a metal housing from an old fluorescent shop light...trimmed for length, would this worK? It's probably 10" x 48" and already arched

The driven element seems to usually be made of copper tubing in the designs I've seen. Can I just make a folded dipole out of copper wire stapled to a board? will the wood interfere? Stranded or solid wire? Bigger or smaller gauge?

I have seen designs where the main beam is non-conductive and isolated from the directors and reflector. I have also seen it all metal and bonded to them. Which way? Bonded is easier

Finally...I am pretty sure this contraption I am about to build will work better than my silly wire currently in use. However, I dont have a signal strength meter and have no way of knowing except to listen. If easily done, will either of these help me measure the signal?
amp.jpg

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Shane
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Re: FM radio antenna

Post by Shane » Wed Dec 14, 2016 12:48 am

It seems you are looking for a long way around what should be a short cut.

Yagis are typically made of lightweight metal. I'm not aware of any reason why the driven element would need to be copper.

The meters shown would not help you by themselves. You would have to make one of them the indicator in a field strength meter circuit which is taking this discussion far beyond scope to accomplish your desired end.

Easy way: buy a commercially made Yagi specifically designed to receive the FM broadcast band and some "twin-lead" feedline (which is what we call the pair of wires you connect between the antenna and the radio), put the Yagi on a pole, point it toward the transmitters you are interested in hearing, connect antenna to radio and enjoy. (I may have left out a few steps but I think you would be able to fill in the blanks.)

Instructive way: Find an old copy of the Radio Amateurs' Handbook. Any year past 1956 should do. Somewhere in there will be fairly complete instructions for building the type of antenna you are looking for (a Yagi - capitalized because it's the last name of the guy who invented it) along with parts lists and theory (how it works including formulas for calculating the lengths of the elements).

A Yagi can have as few as 3 elements (even just two) and as many as needed with the majority of them being directors ahead of one driven element and one reflector. In general, the driven element would be cut to be resonant (a good match to feedline and receiver to keep it simple) at 98 MHz. The reflector would be a little longer; the directors each one a bit shorter than the last with the shortest one at the front of the array. Usually, only the driven element is not electrically connected to the boom, although there are a number of ways to use what's called a matching section so you can skip that formality and making it possible to use coaxial feedline instead.

Using wood is rather quaint. You will actually find some of those construction practices if you go further back into the Handbook annals. Lightweight metals, particularly aluminum, have pretty much made using wood unnecessary.

Two more things if this antenna is going to be outside: neighbors and lightning.

Neighbors have this awful habit of not liking ugly things in other people's back yards (or front yards for that matter). We call this the NIMBY effect, for "Not In MY Back Yard!" although it should be "not in YOUR back yard next to mine!"

Now WE don't consider antennas ugly but most people do. You may even have covenants in your neighborhood you agreed to when you bought the house that prohibit or limit this kind of activity. But then hiding one in a tree is pretty easy.

If you do get the antenna up in the air much at all, you should have lightning protection on the aforementioned "feedline" before it enters the house. The "lightning arrestor" part can be found at your local Radio Shack if you still have one. You will need to supply the ground connection for it. Again, the Handbook will have info for you on that detail.

One last thought. Pay careful attention to what was written above by previous posters about element diameter. Just because you have 1" pipe laying around doesn't mean it's a good choice. In fact, besides complicating calculations, using pipe that's too big may just cause the thing to collapse on itself.

Hope this helps and good luck!
Mike Shane, CBRE
---Omaha---

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