Stridsberg Engineering, LLC
Raven Signals

Shreveport, Louisiana, USA

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Technical Notes & Applications

This section of our web site is a tutorial style technical discussion on the application and specification of receiver multicouplers, as well as on support devices such as pre-amplifiers and receive filters and related components.
The material is mainly from our own R&D, but also from practical field test and experience with receiver multicouplers for a variety of radio monitoring sites.

We expect to include new and useful material for this page on a continuous basis, therefore, it always will stay "Under Construction". If you have a technical or an application question not fully covered here, please email or give us a call, we will be happy to talk to you.


Table of Contents

Introduction
Specifications
Passive/Active
Power Supply

 


Introduction ball-blu.gif (131 bytes)  The most fundamental use of a receiver multicoupler is to enable several radio receivers to utilize a single antenna system without interaction that may degrade each receiver's performance. Many variations in the design concept do exist as well as circuit options, however, signal splitting and the distribution of an RF signal is the basic need to be accomplished.

ball-blu.gif (131 bytes)  Receiver multicouplers may be used for all levels of signal monitoring, from VHF/UHF scanner radios used to monitor agencies, HF receivers to monitor shortwave broadcasts or utility stations, etc. The implementation of  a monitoring system using multicouplers, from HF to VHF/UHF, may range from the level of the serious hobbyist to surveillance professionals engaged in the business of signals intercept and communications monitoring. There are many benefits in using receiver multicouplers but the most obvious one is, of course, that only one antenna system is required to feed several receivers. The inherent technical layout of the monitoring system is further simplified in that only one feed-line is needed, and if a pre-amplifier or a lightning protection device is used, here again, only one is needed to feed banks of monitoring receivers.

ball-blu.gif (131 bytes)  Receiver multicouplers are available in two basic categories, the Passive and Active versions. Both will perform the basic task of splitting an RF signal and feeding several radios without degrading performance of each receiver in the system. The primary difference between a Passive and an Active unit is in how signal losses due to signal splitting is corrected for. That is, normal signal losses always occur in a passive coupler - 3, 6, 12 dB, etc. depending on the number of output ports. Active couplers have circuit designs that correct for these losses in addition to High or Low pass filters for bandwidth control. Therefore, as an example, a 4-port Active multicoupler has no loss of signal from input to either one of its four outputs.  The number of outputs (referred to as "ports") may range from 2 up to 16 or 32, however, standard stock units manufactured by Stridsberg is limited to 2, 4 and 8-port configurations.

ball-blu.gif (131 bytes)   In the "Technical Notes"  section that follows, we will discuss specifications and common applications of the Receiver Multicoupler. It will be helpful in the selection of a specific unit and demonstrate what a receiver multicoupler can or can not do.
We know that each monitoring site has different technical and operational needs, from a few scanners at a home based monitoring post, to, 32 receiver SIGINT platforms (or something in-between). However, there is a common need, antenna signals must be routed to each receiver in such a way as not to compromise the electrical performance of each radio. To meet that need, Stridsberg Engineering manufactures a standard line of Active and Passive multicouplers with specifications and reliabilty that satisfy the requirements of any level of user application.


Specifications ball-blu.gif (131 bytes)   For the majority of of users, specifications of importance are port-to-port Isolation and the coupler's signal loss/gain characteristics. And in the active multicoupler, front-end dynamic specs such as P1dB and 3IP are of value to know. However, the most important specification of a receiver multicoupler (passive or active) is the Port-to-Port Isolation. Isolation is measured in dB and is an indication of how well an output is (signal wise) separated (isolated) from the other output(s). The issue of isolation is very important when several radio receivers are connected to the multicoupler. Most radio receivers will emit RF signals back out (reverse) the antenna. These signals are, unfortunately, a natural circumstance from local oscillators, mixers, PLL synthesizers, etc. Depending on receiver circuit design these "outgoing" signals may be substantial - being strong enough in some cases to be detected by other nearby receivers. Therefore, when using several receivers in a monitoring set-up using a multicoupler, good isolation between ports is important. It ensures that each individual radio is operating without interference from other radios using the coupler. Isolation shall be a minimum of 20 dB for effective use - "the more the better" applies here.

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ball-blu.gif (131 bytes)    Figure 1 above shows how a standard multi-receiver site may be configured. In this case a 4-port unit is used to connect 4 receivers to one antenna. With good isolation between the ports, these receivers will work as they had independent and separate antennas connected to them, and, without interference between radios - the main benefit of the multicoupler.

In figure 2., one method of isolation measurement is shown. This set-up is the preferred one when swept measurements are necessary to confirm isolation over a broad frequency range, example, 25 MHz to 1000 MHz range. All multicouplers manufactured by Stridsberg Engineering are tested this way before release to customer.

ball-blu.gif (131 bytes)    There are, of course, several other electrical and mechanical specification that will determine the performance of a receiver multicoupler, both passive and active models. Among them is signal gain and or loss, signal phase shift (input/output), strong signal handling, power supply requirement, enclosure shielding, etc. Contact Stridsberg Engineering for information on these specifications as it applies to a specific model, or, if they are important or relevant to your specific application.

As mentioned above, in most radio receiving applications using multicouplers, the isolation (rated in dB) is by far the primary parameter of outmost importance. Good isolation will enable multiple receivers to work to its sensitivity specifications, and in the case of scanning radios, not "lock up" on signals emitted from other radios on the same antenna.

Typical Gain & Isolation Performance
MCA202M/204M/208M

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Typical Gain & Isolation Performance
MCA102M/104M/108M

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Passive/Active ball-blu.gif (131 bytes)  Passive vs. Active? In the selection process of a receiver multicoupler the question of whether or not a passive unit can do the job, or, if an active coupler must be used, will have to be answered. In most cases it is relatively easy and straight forward to determine the best choice for a given monitoring site as it is, generally, a question of RF signal strength (or anticipated signal strength) of the transmitters being monitored. For example, if strong HF broadcast stations are primarily monitored, such as BBC, VOA and other international radio stations with substantial signal strength, a passive multicoupler will in most cases do a fine job. Specifically if a large antenna system is used, the passive coupler may be a good choice. If, on the other hand, weaker signals with varying strengths such as those that may be received from clandestine radio transmitters, or from utility stations, is the primary goal of the monitoring effort, an active receiver multicoupler is the better choice.
Stridsberg Engineering offers passive units for both HF and VHF/UHF with up to 4-ports. The larger 8-port multicouplers are  available only as active units due to the excessive signal losses that would normally occur in a passive unit with that number of output ports (-13 to -14dB loss, input to any output port).

ball-blu.gif (131 bytes)   On VHF and UHF frequencies, the active multicoupler is the best choice in most cases. Here, the signal strengths of received signals are, generally, lower than what would be encountered on the HF frequencies. Also, increased losses in the antenna feed-line as the frequency is increased produces lower signal levels at the radio. Specifically, from about 500 MHz and up. Depending on the coaxial cable used, these losses may be substantial. Losses ahead of a radio's front-end (such as in the coax) will directly contribute to system noise figure, therefore, selection of an active multicoupler will not add to those losses as the passive unit would.

ball-blu.gif (131 bytes)  Active receiver multicouplers for VHF/UHF monitoring such as the MCA202M, MCA204M and MCA208M are capable of delivering RF signals to any of the output ports without loss. The frequency coverage of these units range from 25 MHz to 1 GHz, and beyond with slightly relaxed specifications. In fact, the active couplers are useable up to about 1.2 GHz. They are designed with internal amplifiers that corrects for losses, in addition to high-pass filters to shape and control the band-pass on these relatively broadband units. For a monitoring site with several VHF/UHF radios, the active coupler will always give better performance than a passive unit.

ball-blu.gif (131 bytes)  For HF monitoring, models MCA102M, MCA104M and MCA108M are active receiver multicoupler suitable for continuos service from about 100 kHz to 50 MHz. The high end of the frequency coverage (50 MHz) is set by a low-pass filter, thus, protecting the internal amplifier from strong out of band VHF/UHF signals, such as FM radio and TV signals. Although the internal amplifier does not have the benefit of having an AGC signal applied to it at the onset of strong signals, such as a receiver front-end, they are nevertheless designed very robust. Generally, standard models of the active couplers are specified with front-end dynamic numbers of P1dB of +17 dBm and P3IP of + 31 dBm.


Power Supply ball-blu.gif (131 bytes)  All active multicouplers requires +12 VDC/100 mA (nominal) to operate. Because of internal voltage regulation and filtering, this input DC voltage may be between +10 volt and +17 volts. On our standard models, DC power is applied via a common coaxial style power jack (5.5mm/2.1mm) with the center pin positive.

For the North American market, a wall adapter (110VAC/12VDC) is supplied as an accessory. For other countries, using AC power standards of 220 Volts, a DC power plug is supplied for the DC connection, this plug must wired by customer. On request, we can supply this plug wired with about 6 feet of cable for connection to customer +12 VDC power source.

The MCA series of multicouplers are designed to be used in mobile applications as well (surveillance vans, aircraft and shipboard SIGINT/COMINT platforms). If +12 VDC power is available, the multicoupler may be used with the supplied DC plug.For other special DC power requirements, please give us a call.



Page Under Construction

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Please use the email address below to submit technical questions,
request a quote/estimate or other information you may need.
We will respond promptly via email. If you like to be contacted by
phone or fax, please include those phone numbers.
Email:  stridsberg@bellsouth.net


Stridsberg Engineering, LLC
354 Albert Avenue
Shreveport, LA 71105, USA
DoD cage Code: 3RQT1
Tel: (318) 861-0660  Fax: (318) 861-7068
Last modified:
December - 2013