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Old Oct 10, 2014, 06:23 AM
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Thanks Hugo.

Will try building some this weekend
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Old Oct 10, 2014, 08:11 AM
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Also

Was wondering wether to go with a sma t or soldered splice t.
Do you have any advice on your soldered spliced t joint to minimize impedance changes of the cable.
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Old Oct 10, 2014, 08:04 PM
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If 1.2Ghz use SMA, for higher freq. a splice is needed or use 50ohm coaxes and use a gamma match like Alex.

-Hugo
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Old Oct 14, 2014, 09:41 AM
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Hi Hugo

Just wondering if your spacing of 152mm is for 1280MHz.

I will go with 1/4 and 3/4 750hm coax.

My calcs seem too long though for 1280 compared to yours.

1/4 = 58.5 x 0.7 = 40.95
3/4 = 175.5 x 0.7 = 122.85

122.85 + 40.95 = 163.8mm

This is without the length of the sma tee as well.

Are you using slightly different lengths to factor in effect of connectors etc. I don't have access to any test equipment so can only go by calculated lengths.

If I solder the 1/4 and 3/4 75ohm coaxes straight to the antennas and measure between ground elements I get close to 152mm spacing.

Thanks

Chi
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Old Oct 14, 2014, 09:57 AM
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Where did you get 152mm?
I use 164mm just like your calculations.

-Hugo
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Old Oct 14, 2014, 10:06 AM
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Quote:
Originally Posted by Hugeone View Post
The staked fans use the 75/100/50 coaxial transforming/phasing method as described by OMM here

Mine is 1/4-3/4 instead of 3/4-5/4 for less coax loss and it place the antennas 152mm apart for a nice 4.5db gain.

-Hugo
Not sure if these were for 1280.

Also I want to check if it is ok if I solder the 1/4 and 3/4 75ohm lengths directly to the antennas or do I need to have the feed point in line with the ground plane of the antennas.
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Old Oct 14, 2014, 10:22 AM
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Hi Hugo,

Can you, or anyone else, post a sample NEC file that can simulate two antennas like this? Just put two dipoles on each end. I am more interested in how to set up the simulation.

Thanks!

-Ken
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Old Oct 14, 2014, 03:31 PM
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Quote:
Originally Posted by chilau View Post
Not sure if these were for 1280.

Also I want to check if it is ok if I solder the 1/4 and 3/4 75ohm lengths directly to the antennas or do I need to have the feed point in line with the ground plane of the antennas.
Must made a typo...

The fan omni antenna have no ground plane, so I'm not sure of what you mean.

-Hugo
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Old Oct 19, 2014, 10:25 PM
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Quote:
Originally Posted by chilau View Post
Not sure if these were for 1280.

Also I want to check if it is ok if I solder the 1/4 and 3/4 75ohm lengths directly to the antennas or do I need to have the feed point in line with the ground plane of the antennas.
I believe you are referring to the location of the 75 ohm match, correct? If so, they can be anywhere in the system so long as you place the tee at a multiple of 1/2 wavelength (accounting for velocity factor) away from the splice so for RG316/RG179 it would be:

.69 * n/2 * wavelength of frequency

where n = 0, 1, 2, 3, ect.

-Alex
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Old Oct 19, 2014, 10:27 PM
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The above stated, you can also use a stub tune method (use a Smith Chart) or you can use a single section of coaxial cable right at the tee. Remember that the antennas are 50 ohms and so are the feedlines. This means you have a perfect 50 ohms right up until you hit the tee point. It becomes 25 ohms there.

-Alex
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