Re: Antenna switcher and splitter


Robert Conboy
 

The two transformer ones work better. Transformer 1 is 10 turn autotransformer tapped at turn 7. This transforms 50 Ohms to 25 Ohms. (Or 75 to 37.5). The second transformer is 14 turns center tapped.

The 25 (37.5) Ohm tap from the first transformer goes to the center tap.  The two ports are the outer ends of the second transformer.

Place a 100 Ohm (for 50 Ohm system) or 150 for 75 Ohm system across these two outer ends. This provides the isolation between these two ports.

There is only one ground connection - to the cold side of the first transformer.

Isolation and high frequency response can be improved by cancelling out the self inductance of the transformers by placing a capacitor from the center taps to ground.

For BN-73-202  ferrite cores, I arrived at 330 pF for this capacitor experimentally. See


The splitter I described is like fig. 4.


On Oct 7, 2021, at 5:48 PM, LA2PJ - Egil <egil@...> wrote:

Hi Jorge,

I built my own 2-way splitter called "BB-2" in this article:
http://www.dxing.info/equipment/rolling_your_own_bryant.dx

A couple of months later I bought a commercial 5-way splitter (ELAD ASA15).
All signal levels in the homebrew splitter was approximately half an S-unit lower than on the commercial splitter. But with the homebrew unit I'm able to read much weaker signals than I do with the commercial unit. The commercial unit has a built-in amplifier raising the noise floor.

Just one week ago I found this link:
https://www.aliexpress.com/item/4000140516245.html?spm=2114.12057483.detail.3.71be55edpi829d

The price of the chinese unit is is only 25% of what I have to pay here in Norway for the ferrite cores in the homebuilt unit above, so I ordered some of them for experiments. But they'll take another four weeks before arriving here. Looking forward to that.


73
Egil - LA2PJ






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