Here's a topic you hear very little about in amateur circles ... First, let me lay down the ground work. I like boat-anchors. I also like SDR. I also now have a Flex 5000a. So I have a collection of receivers. I also have always been in situations where I had limited space for numerous antennas. So all my receivers generally were connected to my transmitting HF dipoles. So a while ago I discovered something that when I finally tried it I said, "Why didn't I do this earlier?". Having all these different receivers and also restoring and testing others, I noticed that my receive sensitivity and noise floor would change as I connected and disconnected receivers from the "buss" of my receiver antenna feeds. Most times, and like most hams I assume, I daisy chained my coax from one receiver to the next. This way I could use whatever receiver I needed, or several simultaneously. However, I began to notice even changing the "antenna trim" on one receiver would effect the sensitivity of another. Apparently the receivers were interacting. After a bit of digging, I discovered the existence of devices called multi-couplers. Being a boatanchor guy I found an old one made by TMC and these interactions were reduced. Each receiver became isolated from the others and overall gain was restored. Brilliant! Over time my collection became larger, and the types of receivers advanced. These interaction issues while reduced were still a bit problematic once I began using SDR. Birdies became an issue and other interactions that older tube based or early solid state multicouplers were not designed to deal with. The search was on for something more modern. I began looking and quickly I discovered few commercial amateur companies made these. And the ones that did make them offered lesser performance than the Cold War era TMC model I was already using. My guess is the demand isn't there, since many hams probably do not even know these interactions are real or are even present or a problem. Multicouplers work by isolating and splitting an antenna signal. Also if it is an active device it can maintain gain to each output going to each receiver. There is no interaction because gain is at unity and the load presented to each receiver front end is identical and will not vary due to interaction with another receivers front-end. However, active units have a preamplifier on the input, so two things make a big difference in the performance of a multicoupler, reduction of input overload and IMD, and a good 3OIP figure. Most of the products made for amateur use exhibit poor performance in these two crucial areas. After doing quite a bit of searching I discovered a small company down in Shreveport, LA called Stridsberg Engineering. They specialize in military grade receiver optimization devices. Many of their clients are in the fields of radio surveillance, SIGINT platforms and Radio/TV newsrooms as well as clandestine services and the military. They had a device which seemed perfect for my needs; a four-port active HF Multicoupler. The device is small and has BNC connections all around standard. N and TNC types are also available. The model is the MCA104M. The advantages of these multicouplers for this application requiring several monitoring receivers are the port-to-port isolation of the coupler. This will ensure there is no interaction between the receivers, and that the front end of each receiver is properly loaded at 50 ohm. The second obvious benefit in using the coupler is that only one major antenna system has to be maintained, and if a pre-amplifier is used, only one is needed to feed up to four receivers. The model MCA104M is an active multicoupler and exhibits no loss of signal from antenna input to the output ports. This has been achieved by incorporating a broadband GaAs MMIC amplifier driving hybrid splitters, with the addition of precision attenuator pads to balance the gain distribution. A 50MHz low-pass filter on the front end of the amplifier provides up to 50dB of attenuation in the VHF/UHF frequency range to prevent strong undesirable signals to overload the amplifier and possibly causing IMD. So I ordered one and of course had to crack it open to see how it ticks. I was very impressed. The build quality is outstanding. The housing is a black powder coat aluminum with a mount flange. While I had read the description and specifications before ordering, I was surprised to find some very good things not mentioned in the website. The soldering clearly shows these units are made by hand, and the quality of the work is the best I have ever seen, all assembled on a thick FR4 board. All the BNC connectors are Amphenol teflon types. Even the DC jack is high quality. The board also contains a regulator and polarity protection on the DC input. On the antenna input there is even Gas Discharge device to deal with any high-level surges. All the grounding screws as well as the DC and power LED pads are secured with Locktite. All the BNC's use grounding plates to secure then to the enclosure and the board close to each connector. The unit also includes a good RF quiet linear type wall-wart power supply. This item is totally designed & manufactured in the United States. Even the label is not some cheap laser-printed stick-on label. It is a machine printed metal label, perma glued to the enclosure face. I mounted this device to my station copper ground buss bar and connected my Collins R-390a, Hammarlund HQ-110ac-VHF, a RF Space SDR-IQ, and on RX-2 of a Flex 5000A, to the four output ports. Preliminary performance test have been exceptional, with no interactions present and birdies on the SDR's reduced significantly. Noise also seems to be lower. I do have a friend with some Agilent gear I can use to do more thorough analysis and will post those later on. But in my preliminary tests this device performs better than any coupler I have used to date. For now, here are the published specs: Frequency Response: 500kHz to 50MHz Nominal Impedance: 50 ohms Port-to-Port Isolation (min): 22dB P1dB = 17dBm (output), 3IOP = 32dBm (output) Coupler Gain/Loss: +2dB to -1dB (max) over frequency range Connectors: BNC (standard) Mechanical: 4-3/8 X 2-3/8 X 1-1/4 inches (L W H) Case: Die-cast Aluminum, Black Powder Coating Power: +12VCD (nominal) @85mA max. This model with BNC's sells for $185 +shipping. They have several different models with more ports, alternative connectors and different frequency ranges, as well as passive or active variants. You can find this and their other products at http://www.stridsberg.com Sidenote: In order to protect this device (and your receivers, especially SDR's) it is a good idea to use some sort of input overload protection device, such as the DX Engineering Receiver Guard DXE-RG-5000 or similar product. The maximum safe input signal level of this coupler is +22dBm.