If you have a number of shortwave, broadcast and LF receivers and like to run more than one at a time, either for receiver comparisons or tuning different signals, then a multicoupler is a virtual necessity.  It allows several  receivers to share the same antenna with no interaction between them.  That is, tuning one or changing the band on one receiver will have no effect on the other sets.  Neither will you lose signal strength, which will happen when you tie multiple receivers to a common antenna. 
This is the second multicoupler that I've designed and built. Although  the circuit has been simplified and draws considerably less power from the 13.6VDC power supply (about 33mA), it has much better performance than the original.  This is due to the fact that instead of 4 power RF transistors and an RF driver transistor, it uses ONE premium transistor (2N5109) designed for CATV service and the splitting action is accomplished by the use of an MCL 4 way power divider. 
The simplicity and performance comes at a price though.  That MCL splitter costs roughly 40.00 new.   IF you don't need LF response down to <13KC, you can get by with one of the cheaper MCL units that covers a smaller frequency range. It should be mentioned that this power divider is the heart of the unit, insuring isolation of about 35dB between receivers and a power balance between outputs of about .5dB.
The basic circuit is a one stage, low noise amplifier with high Intercept Points and 19dB of gain.  Since a multicoupler should have little or no gain, the preamp is followed by a 6dB, 50 Ohm attenuator.  That insures a good 50 Ohm impedance match into the power divider.  The power divider has 6dB of insertion loss, giving an overall input/output gain of 6-7dB (roughly 1 "S" unit). 
Since the amplifier stage does have 19dB gain over a wide bandwidth it is ESSENTIAL that you follow good RF construction practices in it's construction.  Short leads and a good ground is a must.  "Dead Bug" construction on a copper clad PCB board is good.  I built mine on a small Universal PCB board from Radio Shack and securely mounted it on a piece of copper clad with many grounding staps between the boards.  Keep the output leads away from the input.  Having said that, I had virtually NO stability problems with the unit I built.  
A few construction notes:
1.  The transistor bias is adjustable via R3.  To properly adjust it, adjust the bias control so that the collector (case) of the transistor has EXACTLY HALF as much Voltage as the junction of resistors R6 & R7 has.  I.E., if there is 12.6VDC at the junction, adjust the bias for 6.3VDC on the case of the transistor.

2.  In normal operation the transistor runs quite warm and "should" have a small, finned heatsink attached.  (remember, the case is at collector potential, DON'T ground it).
3.  Diode D1 isn't essential, it is there for reverse polarity protection of the transistor.  Diode type isn't critical either.  Any small rectifier type diode will suffice.

4.  Unit should be mounted in a shielded metal box, and you can use any type of RF connectors you desire.  (BNC, SO-239, RCA etc). I used BNC connectors because of their high quality and ease of installing (single hole mount).

5.  Resistor R4 is there for RF stability and should be mounted right AT the base of the transistor (short leads).

6.  Resistor R5 is there for temperature stability and to provide some degenerative feedback,  DON'T bypass it for more gain.

7.  Resistor R6 actually consists of TWO 390 Ohm, 1/2 Watt resistors in parallel.  They run warm, don't use smaller Wattages (you MAY use a single 220 Ohm, 1 Watt resistor, I didn't have any).
I asked Steve Ratzlaff, a friend of mine who has the equipment to run some tests on this circuit design.  Here is what he had to say after running the tests.
"I've breadboarded and tested the preamp on the bench.

Using a 2N5109, at 13.0VCC, 36mA (runs hot but can hold finger on for several seconds = conservative rule of thumb for need for heat sink, OK as is). The two 390 resistors do run warm, but I used 1/4 watters.  
Below about 2MHz, gain is +19.6db. -1dB rolloff at 14.9Mc and 20kc; -2db rolloff at 31.4Mc and 13.5kc. All these measurements are into well-defined 50 ohms in/out.

Running intermod tests, I get +28dBm 3rd order output intercept (OIP3); +36dBm 2nd order output intercept (OIP2). This is average to above average performance, especially for so much gain, and is much better than most radios, so should be adequate for your usage."
OK, here's the schematic and parts list.

   4X MCL PSC4-6 4 Way power divider
   C1, C2, C3 .1uF 50V Mylar
   C4 10uF 25V Electrolytic
   D1 1N4001 polarity protect diode
   Q1 2N5109 Transistor
   R1 3.3K 1/2W
   R2 180 Ohms 1/2W
   R3 470 Ohms Variable
   R4 10 Ohms 1/2W
   R5 4.7 Ohms 1/2W
   R6 2ea 390 Ohms 1/2W resistors in parallel
   R7 10 Ohms 1/2W
   R8, R10 150 Ohms 1/2W
   R11 39 Ohms 1/2W
Melt Some Solder!
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