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Old 14th June 2005, 12:51 AM   #11
homer09 is offline homer09  Canada
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the back
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Old 14th June 2005, 12:52 AM   #12
homer09 is offline homer09  Canada
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the dipole i use (obviously i stretch it out and orient it as best i can)
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Old 15th June 2005, 01:53 AM   #13
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Ah, I thought as much. I too have one of those nasty ribbon antenna's. And my one is crap .

So there's hope for you yet!

This site shows you how to build a similar antenna, but tuned closer to your weak station. I'd try that first as its quick, cheap and easy.
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Old 15th June 2005, 03:53 PM   #14
homer09 is offline homer09  Canada
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Quote:
Originally posted by TwoSpoons
Ah, I thought as much. I too have one of those nasty ribbon antenna's. And my one is crap .

So there's hope for you yet!

This site shows you how to build a similar antenna, but tuned closer to your weak station. I'd try that first as its quick, cheap and easy.

Thanks, i will try this!

will connecting the crossbar of the antenna with 75-ohm coax be better than using more 300 ohm twin lead? i noticed the apparently very good FM Reflect dipole from C. Crane

http://www.ccrane.com/fm-reflect-antenna.aspx

uses 75 ohm to terminate. any other insight between the differences between this FM Reflect and a standard dipole?
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Old 15th June 2005, 07:19 PM   #15
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Quote:
Originally posted by TwoSpoons
Ah, I thought as much. I too have one of those nasty ribbon antenna's. And my one is crap .

So there's hope for you yet!

This site shows you how to build a similar antenna, but tuned closer to your weak station. I'd try that first as its quick, cheap and easy.
What's the difference? Is the 300ohm wire much better than that used in the ribbon antenna?
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Old 15th June 2005, 07:23 PM   #16
dnsey is offline dnsey  United Kingdom
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As Twospoons pointed out, a straight dipole is terminated at 75 Ohms, and a folded dipole at 300. (Actually it's a bit more complicated, especially if you start adding elements...).
What the DIY site describes is a folded dipole:

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so it needs a 300 Ohm cable.

The Drake looks like a straight dipole:



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and will therefore require 75 Ohm cable.


EDIT: The site doesn't like my diagrams, but I hope you understand what I mean!
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Old 15th June 2005, 07:26 PM   #17
homer09 is offline homer09  Canada
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Quote:
Originally posted by jimbo1968


What's the difference? Is the 300ohm wire much better than that used in the ribbon antenna?
i have read that some wire used in cheap dipoles doesnt even have 300ohm impedence, some have closer to 200. thats one improvement.

second, my dipole is almost 6' long, which is terrible considering that is optimized for 78 MHz, when FM is 88-108 MHz and my problem station is 99.9 MHz. this will be the second improvement.


Still wondering about that FM reflect antenna and if anyone has any insight on how it is built inside?


Click the image to open in full size.
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Old 15th June 2005, 07:29 PM   #18
homer09 is offline homer09  Canada
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Quote:
Originally posted by dnsey
As Twospoons pointed out, a straight dipole is terminated at 75 Ohms, and a folded dipole at 300. (Actually it's a bit more complicated, especially if you start adding elements...).
What the DIY site describes is a folded dipole:


so it needs a 300 Ohm cable.

The Drake looks like a straight dipole:

and will therefore require 75 Ohm cable.


Sorry what is the "Drake" is this the antenna i just posted a pic of? Because if it is, this one looks like a folded dipole to me, notice in the picture there are two runs of coax... how could it be using 75 ohm then?
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Old 15th June 2005, 07:31 PM   #19
homer09 is offline homer09  Canada
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another pic of the FM Reflect

Click the image to open in full size.
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Old 15th June 2005, 08:09 PM   #20
dnsey is offline dnsey  United Kingdom
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I have no idea where I got 'Drake' from!!

I was referring to the FM Reflect, which looked to me like a straight dipole, but I see from the larger pic that it's not.

As I said, it's not really as straightforward as all that (what is?) - the impedence actually varies with the point of attachment of the feeder. It's also quite possible that the two runs of the Reflect are not electrically conected - one may well be acting as a parasitic element.
The best feeder for a simple ribbon folded dipole, however, is 300 Ohm.

I'd be a bit dubious about the reports of some feeders being 200 Ohm - it's possibly so, but not an easy thing to measure, and will vary according to various extrinsic factors, so I wouldn't worry too much.

Just for fun, I've read that a pair of 'Slinky' spring toys arranged as a dipole can be very efficient - might be worth a try: cheap copies are available here in 'Pound Stores'.
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