DIY FM antenna, can it be better than radioshack junk?

[Illusus]

'Black Satin'* paint

Oh, I forgot about the asterix... OT story... near my home, some fools spray painted "SATIN RULES" on the side of a church. I'm sure they meant to write satan rules but satin is just so funny. Alas, the graff was gone by the time I came around with a camera.
Fools:
- "Dude, I just love satin...it's so smooth!"
- "F!'n A, man! Satin rules!! Praise satin!"

[TwoSpoons]

i am very confused when researching j-poles because they are mostly used for HAM and transmitting. i want to receive signal and have no idea where this all fits in.

Antennas work equally well transmitting or receiving - i.e. a good transmitting antenna is also a good receiving antenna. Otherwise it would disobey one of the laws of thermodynamics!

From the sites I've seen
1. 300 ohm ribbon varies widely in velocity factor, its not a parameter controlled during manufacture. So calculating the right length is going to be tricky.

2. fatter conductors = wider bandwidth, which is want you want for receiving FM.

3. A j-pole is an end-fed half-wave dipole, with a quarter-wave matching stub. It can be built as an end-fed 5/8th wave, but tuning is supposedly more finicky. J-poles are nicely ground independent.

4. Velocity factor for 1/2" copper pipe is about 0.95, at 98MHz

Kind of random, but that summarises some of the stuff I've found.

[jackinnj]

Originally posted by TwoSpoons


Antennas work equally well transmitting or receiving - i.e. a good transmitting antenna is also a good receiving antenna. Otherwise it would disobey one of the laws of thermodynamics!

But a transmitting antenna is built to take anywhere from a few watts to two kilowatts for ham use -- so the materials might be different -- this becomes problematic for yagi's and LPDA's where you have to contend with wind and ice-loading.

Most university libraries (and county libraries in the U.S.) will have a copy of "The ARRL Antenna Handbook" -- this is a great source of theory and practice. The book costs around $39 and comes with a CD-ROM of programs which put the calculations into some easy programs (although many of these are java-scripted for the web nowadays.)

It surprises me that there have been relatively few articles on FM and AM antenna's -- a couple years back there was a nice article in EW describing how a.m. radio buffs in the UK built multiple loop antennas in order to hear bluegrass from the U.S. I think that AudioXpress and its predecessor have only had a half-dozen articles in the past 30 years or so. I have only been receiving Elektor for 4 or 5 years and would be interested to find out if they have any good FM antenna articles.

[Scott Stansbury]

The ARRL is definitely the source for all the info you need. The ARRL Antenna Book is the bible, and the site itself has good info. Check out:

http://www.arrl.org/tis/info/antproj.html

Any step in the direction of a real antenna will produce good results.

Best regards.

[gengis]

Has anyone tried those car antenna that extended automatically when the radio is turn on? Go down to the junk yard and pick out a late model cadillac, and take out the antenna.

That would be pretty cool.

[homer09]

hmmm. i guess it would be "cool" but what about performance?

[gengis]

It should be fine. Just like any rabbit ear antenna.

[richie00boy]

Just bookmarking this thread as I want to build an FM aerial soon.

[homer09]

Originally posted by richie00boy
Just bookmarking this thread as I want to build an FM aerial soon.

be sure to report back with your experiences!

[richie00boy]

I promise I will, but it will be a few months yet, too many other jobs to do...