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Author Topic: Distance between 2 dipoles  (Read 886 times)
KC9ATJ
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« on: August 12, 2007, 10:29:42 AM »

I am running a special event station for my local Boy Scout Council and am wanting to be working both 20 and 40 at the same time.  I figured for this temperary setup I would use two dipoles (one for each band).  I'm wondering what would need to be the minimum distance between the two dipoles so that I don't create interference between the two radios.
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KB9CRY
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« Reply #1 on: August 13, 2007, 06:59:14 AM »

Probably a few miles.

Depends on the radios but what you'll want to have are bandpass filters on each.

Check out either Array Systems or ICE (Industrial Communication Engineers).

Many folks also make their own. Search for details on Google
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AA4PB
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« Reply #2 on: August 14, 2007, 05:36:00 AM »

Impossible to answer because it is so dependent upon the particular radios and how much interferrence you might be able to tolerate. Band pass filters will certainly help. As a wild guess, I'd think that most radios would be okay with say 20-30 foot separation for 20M and 40M. More is always better.
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KC9ATJ
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« Reply #3 on: August 14, 2007, 06:09:28 AM »

I am planning on using IC730 and IC706 for the two radios.  They will be putting out 100 watts.  I will definately look into band pass filters.
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N4OGW
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« Reply #4 on: August 14, 2007, 10:04:35 AM »

It depends...I have a 20/40m beam (Force12 EF420-240) that has interlaced elements for the two bands on the same boom with only a few feet of separation between them. With bandpass filters and coax stubs I use both bands simultaneously during contests.

The isolation between the antennas will increase if you can orient the dipoles perpendicular to each other, or if you use a vertical for one band and a dipole for the other.

If you are only going to use two bands and low power, a simple coax stub for each radio will be plenty of filtering and much cheaper than a bandpass filter.

Tor
N4OGW
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KC9ATJ
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« Reply #5 on: August 18, 2007, 06:10:48 AM »

I thought that coax stub was used for tuning and not filtering.
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AA4PB
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« Reply #6 on: August 20, 2007, 06:31:51 AM »

If you make a coax stub 1/4 wavelength long and short one end, it will be a band-pass filter. If you leave the end open then it will act as a band-reject filter.

A short on one end of a 1/4 wavelength results in a high impedance at the other end. On open on one end results in a low impedance at the other end.
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