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FM helical antenna DIY
FM helical antenna DIY
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Old 2nd January 2018, 01:07 PM   #11
Pano is offline Pano  United States
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FM helical antenna DIY
Not in my area. I'm not sure there is even a station withing DX range what would be worth listening to. Those days are long gone - such a shame.
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Old 2nd January 2018, 01:50 PM   #12
scott wurcer is offline scott wurcer  United States
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Originally Posted by Pano View Post
Not in my area. I'm not sure there is even a station withing DX range what would be worth listening to. Those days are long gone - such a shame.
OTOH you can webcast them, try Howie's feed. You might not like all the shows.
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Old 2nd January 2018, 02:16 PM   #13
Speedskater is offline Speedskater  United States
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Just about everything most people need to know about FM antennas:
88?108 MHz

And yes, US FM radio is circularly polarized.
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Old 2nd January 2018, 02:22 PM   #14
Tubelab_com is offline Tubelab_com  United States
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Why helical?? FM transmission is either horisontally or vertically polarized
FM radio in the US was universally horizontally polarized until car radios began to include FM (late 60's). In order to best reach this market without considerable investment, a new antenna design was invented that did radiate a fraction of it's power in a variation of circular polarization. It offers a good compromise to vehicle antennas which were usually 1/4 wave whips offering a weird pastern due to the uneven offset ground plane created by the car body. Today's car antennas are essentially a very now noise amplifier with a short random wire antenna attached. They tend to suck too.

helicaly wound around a wooden dowel rod.
An axial mode helix would receive off of its end, exhibit gain over a dipole, but must have a diameter that is a significant fraction of a wavelength. A wire wrapped around a dowel is not an axial mode helix.

A normal mode helix is essentially a shortened monopole antenna which will not exhibit gain. It can however have a reduced radiation angle which appears as "gain" under the right conditions.

I built a super stick tuned to the 27MHz bandwidth. An old fishing rod with the antenna also helical wound
I made a few fishing rod antennas as a kid for my CB. The idea was more about hiding the antenna from my parents than maximum signal. Two 5 foot fishing rods in the attic fed in the center made a decent 1/2 wave dipole.

I'm not sure there is even a station withing DX range what would be worth listening to.
I used to pick up a decent classis rock station from Ft. Meyers several years ago.......but it is now probably owned by Clear Channel / I Heart and reduced to a 200 song play list.

That's what happened to the classic rock station in Ft. Lauderdale and here locally in Wheeling. Both have short play lists, similar but with a few differences. You will hear Free Bird and Sweet Home Alabama here once a week.

Then they wonder why nobody buys CD's any more. If I heard something on the radio I liked, I might buy it. But with 200 songs that are all at least 10 years old, I have already heard them all many times. I either have the CD, or don't want the CD......play something different guys!
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Old 2nd January 2018, 03:25 PM   #15
DF96 is offline DF96  England
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Originally Posted by 70s Veteran
The box height was limited to be 12" so as I didn't want a fragile whip antenna I mounted the antenna inside it.
OK, that explains why you needed a compact antenna. A normal-mode helical will work, but not much better and not much worse than any other compact antenna. We will pass over claims of '5/8' and '6dB'.
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