Homebrew FM Radio antenna

[ratdude747]

I finally am getting around to posting this..

what happend was i bought a magnavox mini system for $15 at a thrift store. it was that cheap because it was coved in spongebob stickers (easy fix), and missing the remote and antennae. i also found a different brand antenna to fix that problem or so i thought...

turns out dipshit over here was hooking an AM loop to the FM connection :faceplam: i always wondered why my reception was so bad... until an off topic physics discusioon this spring lit a bulb in my head...

what went wrong was the AM connection used a pwer supply fan type connector and the FM used bare Lead connections. the AM loop had bare leads. easy fix... snipped a lead off off a dead fan from a gutless psu and soldered and taped it.

which left me w/o an FM antenna. i decided i would make it homebrew... first, i decided to make each wire coil around an insulative frame, coing away from each other. for a frame, i found that a plastic pants hanger fit the bill... it had a place to tie wire off and a way to keep the the coils separate. as an added bonus, the hook ansd clims made it so i could either hang it or clip it to a shelf.

it was made and has worked well... i get a very strong signal in my basement, which iirc is a low signal area.

a pic of it:



any comments/ suggestions?

[Radio Fox]

Re: Homebrew FM Radio antenna

You would probably get better reception if you slung up a dipole antenna of the correct length. You have too much wire on that hanger for FM reception.

Idealy the impedance of the antenna should be 300 Ohms. You could construct an antenna using 300 Ohm ribbon cable of the correct length, or it may be cheaper to buy a ready-made one.

The next best thing is to construct a half wave dipole out of something you may already have to hand, such as speaker wire or twin mains flex, where the 2 wires can be pulled aprt & seperated into a "T" shape.. The total length of a half wave dipole is 468/f(MHz), which, for the centre of FM band II is 4 feet 9 inches.

[stj]

Re: Homebrew FM Radio antenna

you want to get the antenna up in the loft,
height will help more than design.

[ratdude747]

Re: Homebrew FM Radio antenna

it is a finished room, nowhere to hang it.

it is working fine so i am leaving it as is.

i have yet to see premade antennas anywhere...

[delaware74b]

Re: Homebrew FM Radio antenna

Ratshack has one if you're willing to part with $7.

Here's the link: http://www.radioshack.com/product/in...ductId=2062691

[PlainBill]

Re: Homebrew FM Radio antenna

it is a finished room, nowhere to hang it.

it is working fine so i am leaving it as is.

i have yet to see premade antennas anywhere...

#1 rule of engineering. If it works, you did something right. On the other hand, a lot of these just use a length of wire - 30" IIRC.

PlainBill

[ratdude747]

Re: Homebrew FM Radio antenna

The next best thing is to construct a half wave dipole out of something you may already have to hand, such as speaker wire or twin mains flex, where the 2 wires can be pulled aprt & seperated into a "T" shape.. The total length of a half wave dipole is 468/f(MHz), which, for the centre of FM band II is 4 feet 9 inches.

it is speaker wire... they do split in a T... do some math, i think my wire lengths are close to ideal... it is just a compact version.

[cadiman]

Re: Homebrew FM Radio antenna

fm is 32" and am should be around 48" Think automotive

[romansroad]

Re: Homebrew FM Radio antenna

I like this build! It's compact and will keep your tee-shirts off the floor as well. MI-6 no doubt will be interested

I've studied/built countless am loops and high gain directional fm loops. The ARRL handbook has some great designs, and you can tune them to your desired freq range. I prefer the multi-element loops, but they are by their design, directional.

Agreed that altitude is your friend, but if you have no access, that limits it some. If you wall access, you can slip up a wire in that space along the outside wall, and you'd be surprised how well it works. Keep in mind that there may be 110v lurking in there, so safety first and you may get some 60 cycle hum.

I recall that C. Crane company had a decent selection of pre-made antennas (but what's the fun in that!?) so take a look there. Overall, Plain Bill is right (no surprise!) and it looks like you've done it right if its working. I've found FM to be a bit capricious at best, and even my superior designs (IMHO) could get trumped by a dipole some days! Go figure....