I recently designed this multicoupler for use on 3 to 30Mhz. It's purpose is to be able to use one antenna and two receivers. I am using the NE5539 as I had some in my personal stock. The NE5539 is used as a gain stage feeding some emitter followers.
My questions are:
1. Do I need a resistor between the output of the NE5539 and the input of the emitter followers to prevent oscillation.
2. Or can I just connect the output of the 5539 directly to the input of the emitter followers.
3. Are the bias resistors for the 2N2222 the right values?
4. Is the output impedance of the emitter followers 51 ohms?
Any and all suggestions welcomed.
Schematic and data sheet of NE5539 attached.
Ned

Attached Images

MULTICOUPLER SCHEMATIC.JPG (33.2 KB, 10 views)

Attached Files

NE5539.pdf (170.4 KB, 4 views)

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First of all, I have to ask the question, "What antenna will you be using?"

If it is anything other than a short wire or loop, I see overload and intermodulation rendering the whole scheme useless.
Feeding a 30 foot long wire antenna into the 5539 will almost certainly result in driving the amp into non-linear operation if it has any gain.

Depending on the antenna, I would just use a resistive splitter.

JimB

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Jim, thanks for your reply. I plan to use the coupler between the 50 output of a auto tuned coupler and a pair of receivers. I think the most gain will be 6db.

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The great thing about electronics is unlimited ways to do the job. The only limit is one\'s imagination. I generally think my way is best.
Show me a different way. I have an open mind.

 

You need a bandpass filter at the amplifier input. Use a passive splitter instead of the two transistors:

A better type:

Which is from this page about 1/2 way down:
http://www.w8ji.com/combiner_and_splitters.htm

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Just one problem with that scheme, an auto tuning ATU requires something to tune with, ie a reasonably large signal from a transmitter.
You dont mention a transmitter.
Auto tune ATUs are no good for receive only applications.

JimB

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Experience is directly proportional to the value of the equipment ruined.