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Stridsberg Engineering HF Receiver Multi-Coupler

Discussion in 'Amateur Radio Equipment Reviews' started by W2WDX, Aug 10, 2018.

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  1. W2WDX

    W2WDX Ham Member QRZ Page

    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.

    Stridcoupler1.JPG

    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.

    Stridcoupler2.JPG

    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.
     
    Last edited: Aug 10, 2018
    KB4QAA likes this.
  2. W2WDX

    W2WDX Ham Member QRZ Page

    One other important thing I forgot to mention. These devices are only to be used in situations where you have a receive antenna feed that is separate from your transmitter. So these devices must be used on some type of T/R switching arrangement. They cannot be put inline with a transceiver and do not have any type of internal relay or bypass for transmit. You cannot put power through them.

    This arrangement is similar to what is used for a mast mounted pre-amplifier. Similar sequencers, relays and such can be used in the same way, or old school T/R switching used when you have a separate transmitter and receiver can be employed.

    My arrangement is I use the internal T/R delayed release relay in an unmodified Johnson KW Matchbox, of which there is a separate terminal strip for the receive antenna line. This goes through a small 6:1 balun to transform the 300 ohm output to 50 ohm, which is then fed into a DXE Receiver Guard, then into the multi-coupler and onto the various receivers.
     
    Last edited: Aug 10, 2018
  3. VK4GAP

    VK4GAP Ham Member QRZ Page

    That looks well made , i also in the past have used several SW radios via 1 antenna , i used to make up my own splitters altering catv and network splitters , some worked out ok , some preamp , some with balance amp , some passive , some not so good due to the size of the transformers and the difficulty rewinding them but overall it was good fun (i no longer use them due to cleaning out the collection) , i did once see a splitter on ebay a few years ago from one of the base's down there at Antarctica , it was humongous and had several fixed and 2? adjustable outputs ports and if i recollect properly had 10 outs with 2 ins all switchable for on or off , i should have bid on it , it was amazing 1980-90's era stuff . 73 , Paul
     
  4. W2WDX

    W2WDX Ham Member QRZ Page

    Originally I was using a TMC multi-coupler which dates back to the Cold War era. It had about a dozen outputs. Here's an image, the coupler is below the Johnson Matchbox.

    station042011c.jpg

    It worked fine until I started using SDR. It didn't take care of birdies coming from the older receivers into the SDR. This new unit took care of all of that.
     
  5. KB1NXE

    KB1NXE Platinum Subscriber Platinum Subscriber QRZ Page

    They also have one for VHF to UHF (25 - 1000 MHz). The MCA204 or 208 (4 or 8 ports). Great for multiple scanners.
     
  6. KD4MOJ

    KD4MOJ Platinum Subscriber Platinum Subscriber QRZ Page

    They make good stuff... expensive but worth it. I have the MCA204M which I use for aircraft receivers.

    ...DOUG
    KD4MOJ
     
  7. KL7AJ

    KL7AJ Ham Member QRZ Page

    I've used hybrids and splitters for ages, and properly designed ones work very well. Just be aware that for a 4:1 divider, each signal will be attenuated by 6 db over the the input port....or about an S unit loss.
     
  8. W2WDX

    W2WDX Ham Member QRZ Page

    It is not a divider or splitter. It's an active multi-coupler. The outputs on this specific example are actually about +1.5dB on each output above the input and completely isolated from each other. There are no losses, in fact there is slight bit of gain. That's why you use an active device like this, not a passive divider. It's much more complex than a simple splitter or divider.

    Yes ... I agree for a small device that takes care of something not so critical it is expensive. However, when you purchase something and its quality of manufacture and performance are exceptional the price becomes less of an issue. When you consider all the really badly assembled and designed stuff being offered for hams these days, it's very nice to get something that is built very well, at any price. IMO opinion, because I prefer to have these devices (because if you can't here them you can't work them) the quality of this one is well worth the price.
     
    Last edited: Aug 10, 2018
  9. SM0AOM

    SM0AOM Ham Member QRZ Page

    The hybrid splitters are preceded by an MMIC broadband amplifier for compensating the splitting loss.

    This causes a certain problem with multicouplers of this general form,
    the IP3 performance of MMIC:s can be impressive, but the IP2 is not.

    So, if you connect a multicoupler of this type to a large broadband antenna, especially in Europe,
    be prepared to find lots of second-order products.

    This is the reason for the steep prices for really good multicouplers, such as those from Raven Research and TCI.

    They have to be built using balanced feedback amplifiers having lots of resting current to have IM2 properties that are better than the good HF receivers.

    73/
    Karl-Arne
    SM0AOM
     

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