Views / News – Blog

Merry Christmas

@YellowsBestLtd we would like to thank our Customers for your enquiries and orders throughout this year, as well as our Suppliers for your support.

We’re pleased to have been of assistance providing services and solutions. Now into our fourth year of trading, we appreciate your continued interest and support, and look forward to continuing our business relationship in the New Year ahead.

Wishing a Merry Christmas to you and your family.  

Nokia ‘Dynanet’ Telecoms – Stock disposal

‘Last chance’ for spares!

The Nokia ‘Dynanet’ family of PDH Transmission telecoms products has served customers well for the last 20+ years, and indeed some networks continue providing good operational service. 

Dynanet Subtrack

@YellowsBestLtd has supported requirements to maintain these networks by supplying various spare part items from refurbished and surplus stocks in perfectly working order.

However, demand has recently reduced and warehouse space is needed, so now the time has come to recycle / dispose of a large proportion of the remaining equipment. Consequently, there remains a short-term opportunity to obtain any items still required to maintain existing deployed infrastructure, before the products are gone.

Here is a stock list of the main items currently available, though there may be a few additional parts that can be supplied. Hence, please check and if you do have any requirements, please let us know – before it’s too late! We look forward to hearing from you.

Part  NumberDescription
24204TPSO H/W Module
CC 24002DB2 Branching Unit, B2 2×2 Mb/s 75 ohm
CC 24011DB2 2 Mb/s Switching Unit, X2 75 ohm
CC 24101DN2 Interface Unit (IU2) 2×2 Mb/s 75 ohm
CC 24111DN2 Control Unit (CU) 75 ohm
CF 24186DN2 19″ Subrack
CF 24186.09DN2 Subrack 19″, grey-L91 EMC
CG 24170DN2 Bus Power Unit (BPU)
CG 24171Extended DN2 Bus Power Unit (EBPU)
CU 24013Data Interface Unit (DIU) 2M, nx64k: G.703/704, 75 ohm
T30506.0917-slot DYNANET Subrack
T30851.02Subrack Power Adapter (SPA)
T37870.01NDM ACM2 19in 17-slot subrack
T37871.01NDM DN2 19″ 17-Slot Subrack
T37882.01NDM DC Unit (NDUe)
T37882.02NDM DC Unit (NDUe)
T37885.01NDM Ring Generator
T37889.01NDM Backup Unit (NBU)
T65520.01ACL2 RM DC Power Gen
T65580.01ACL2i PF GEN Line Terminal Card
TA 21513Optical Line Terminal Repeater 2-8 M, 1300 nm LED MM/SM
TA 21516Optical Line Terminal Repeater 2-8 M, 1300 nm LASER SM
TC 21101DM34 Mux Card
TC 21301DM8 Multiplex Equipment, 75 ohm
TC 21705Supervisory Substation
TC 21710.01TMS Adapter
TG 21261Ring Generator 25HZ 15W
TU 21122.5Data Interface Unit (DIU) 48..64k V.11 10ch
TU 21124Data Interface Unit (DIU) NX64k V.11/V.35/X.21 2CH
TU 21124.05Data Interface Unit (DIU)
TU 21125Data Interface Unit (DIU) 48..64k with sync, X.21
TU 21205Channel Unit SUB/SUB
TU 21206Channel Unit SUB/SUB
TU 21215Channel Unit SUB/EXCH
TU 21216Channel Unit SUB/EXCH
TU 21234.20Channel Unit E&M/VF-P, 10 CH, 20 E&M CH
TU 21236.10Channel Unit (CU) 8ch E&M/uP: 2xe&m/vf
TU 21255.01Channel Switch, 4 PORT
TV 21640.08Power Interface Adapter DC

Three years milestone

Three years completed; onward in our fourth year!

@YellowsBestLtd has now reached the significant milestone of completing three years of trading; something often useful to be able to state when qualifying for opportunities and registering with business customers.

Our aim continues to be “Keeping Customers Operational”; understanding requirements and fulfilling them by providing a range of management services and solutions, including:

  • consultancy, such as business development planning3_years_services
  • technical support, e.g. day-rate engineering, NMS assistance
  • systems supply, including legacy IT servers / workstations
  • spares for infrastructure, in particular telecoms and CCTV cameras
  • repairs at module and component level, e.g. LED displayboards
  • value recovery through reverse logistics, resale and recycling

As we move forward in year four, we’d very much like to discover what else to provide to our existing Customers, as well as what would be of interest to potential clients. We’re always keen to enhance our range of #business services, increase the #enterprise infrastructure we support and expand our mix of #sustainable solutions we offer for supply and maintenance of new and legacy #technologies and products.

Please get in touch to discuss your challenges; whether you’re implementing new systems or maintaining existing infrastructure to serve your operational business needs. We look forward to hearing from you.

Solar energy project

“Off-grid eCharger”

The aim of this ‘off-grid’ solar energy project was to build a charger for an eBike so that its battery could be charged (when not in use) from power collected from the sun via a ‘fixed’ off-grid installation, rather than relying on mains energy. This can also be used for other battery charging and small backup supply purposes.

Four main elements were put together to create the solar charging ‘system’:


Solar Panel

This fundamental part performs the key task of converting sunlight into electrical energy. There is a wide range of panel types to choose between. Firstly, sizes include the very small, through 50W, 60W, 80W and up to 100W. Thereafter, systems are typically built from connecting multiple panels together.

Solar Panel
50W Mono Flexi Solar Panel

Then, there are four main types of solar array:

a) Poly Crystalline – cheaper to manufacture, sensitive to high temperature, less efficient with a shorter lifespan
b) Mono Crystalline – more expensive, more efficient, with a longer lifespanc)
c) Thin-Film Amorphous (A-Si) – flexible, lower cost – easier to produce, shorter lifespan, lower power
d) Concentrated PV Cell (CVP) – very high performance, solar tracking and cooling required, very expensive.

Finally, there is the choice of construction type:

i) Rigid – cheapest and most solid, heavy and longest lasting
ii) Flexible – PET – light-weight and bendy, ideal for vehicles and temporary installations
iii) Flexible – ETFE – longer lasting, marine grade, can be walked on.

For this project, the aim was to use something lightweight that could be easily attached to an existing small building structure by means of the re-enforced ringlets in its corners (not all panels have these, so choosing had to be careful), rather than a permanent roof-top installation, and so the Flexible PET type was indicated.

After some consideration of likely ‘sun-hours’ – estimates tend to indicate an average of 2-3, depending on the season and weather – and also cost, a 50W 12V Mono Crystalline Flexible PET panel was selected. This size could prove to be an under-estimation for the task, but this can be supplemented later as necessary since its possible to join panels in parallel to increase current (or series, to increase voltage). That will require ‘T’ or ‘Y’ joining pieces for the MC-4 solar cable connectors, and potentially in-line fuses to protect separate ‘strings’ of connected panels (on their own they don’t need the fuses since their short-circuit current rating is sufficient).

If a panel becomes partly shaded, its whole output diminishes. Hence the advantage of having separate panels is that they may contribute more energy individually that using one large single panel. Another aspect is that it is likely that the cost of solar panels will reduce over time, and so adding to the system over time makes sense, rather than trying to ‘future proof’ the power requirement.


Charge Controller

The task performed by this element is to ‘condition’ the output of the solar capture, converting an unregulated supply of around 18V (for a single panel) to a more stable 12V, the energy from which can be directly used or stored in the battery. The use of a controller avoids the risk of over-charging of the battery or issues with varying power, and will shut off its output to the loads when the supply is diminished and the battery is discharged. There are many models, which vary in power rating and functionality, some with simple LED displays and others showing a range of information, and may include sense terminals for long cable runs, temperature measurement for adjustment due to the weather and equalisation functionality for spreading charge across multi-battery systems.

PWM Charge Controller
PWM Charge Controller

The controllers fall into two main types:

a) PWM – Pulse Width Modulation

b) MPPT – Maximum Power Point Tracking

The latter of these is much more efficient, likely to convert more of the captured solar energy into stored power. However, these tend to be at least 3 times more expensive, often much more.

A modestly–priced (reasonably-functioned) PWM unit was selected for this system, with a 20A rating (more than enough for the initial project requirements). The reasoning for this product selection is this: with a small system, should the captured energy be not enough, then purchasing additional panel(s) to increased the wattage is more cost-effective in terms of energy produced, compared with the gain from the more efficient controller. It only becomes worth purchasing the MPPT version when much more energy is being generated (and therefore ’lost’ with a less efficient charge controller).The controller model selected is capable of both 12V and 24V operation, which allows for the increase the voltage rating of the system if desired in the future.



The traditional choice for this type of storage application is the ‘Lead-Acid Cell’, though it needs to be of a Deep-Cycle ‘Leisure’ variety, which is intended to be frequently discharged and recharged, rather than the ‘starting’ classification which is used in a vehicle for short-bursts of energy to get a motor running, after which its mainly in stand-by and therefore expected to be 100% charged most of the time.

AGM Battery
AGM Battery

Apart from this distinction, there are two main types of product:

a) ‘Flooded’ Wet-Cell or Valve Regulated Lead-Acid (VRLA)

b) Absorbed Glass Mat (AGM) or Gelled Electrolyte (Gel)

Of these, the Wet-Cell traditionally required periodic ‘maintenance’, topping up with fluid, though VRLA sealed versions are now available, and tend to ‘vent’ gas and can’t be tipped over due to the fluid inside. The AGM and Gel types however are available maintenance-free, don’t ‘vent’ gases and don’t have fluid that can spill out.

The AGM-type was selected for this project as, whilst being a bit more expensive, offered the convenience of a product shouldn’t require special attention; these are less sensitive to over-charging and can stand for 30 days totally discharged without harm.

There are a number of measurements of the capacity and capability of batteries:

  • Reserve Capacity (RC) is how long the battery can deliver a constant current of 25A at 80F
  • AmpHour (AH / C20) represents how much charge is stored. It is the energy delivered continuously in 20 hours at 80F without falling below 10.5V
  • Cold Cranking Amps (CCA) is a measure of the ability to start an engine cold. It is the number of Amps delivered at 0F for 30sec by a 12V battery whilst maintaining at least 7.2 Volts

A capacity of 110AmH was chosen for this project.  Whilst ‘the more the merrier’ in terms of storage is certainly the case, this capacity should be sufficient for the basic storage needs.  It is advisable however to allow for discharge of only 50% of the stated rating, whilst also bearing in mind the possibility of a few days without sun.

It is possible to add batteries in Parallel to create more storage, or in Series to increase the voltage of the system. For a modest system set-up, 12V is sufficient and convenient for the purpose. Adding another battery to double the system voltage to 24V would have a side-benefit of requiring lower gauge of wiring.



In order to convert the 12V DC power generated from the Solar Panel and stored in the battery, to the 240V AC required by the Load, the Li-Ion battery charger adapter, an inverter is needed. This wouldn’t be the case if a suitable 12V charger-adapter could be sourced, which would avoid the inefficient ‘double-conversion’ of 12V DC into 240V AC and back into 42V DC again. The inverter does however provide the flexibility for powering other equipment requiring an AC ‘mains’ supply and therefore is ideal for a range of charging and backup tasks.

PSW Inverter
PSW Inverter

Apart from the selecting the correct voltage, which is normally either 12V or 24V (12V required to fit with this system set-up), there are two main choices:

a) Modified Sine-Wave

b) Pure Sine-Wave

The first type is the low-cost product, and available in a wide range of power-ratings, so if high-power is required then that tends to be the preferred choice. The draw-back is that it is less-efficient, creating a ‘blocky’ AC waveform which can upset sensitive equipment. The second type produces a smooth sinusoidal AC waveform equivalent to the standard AC ‘mains’ supply, and therefore is suitable for all equipment types, though at higher cost and usually lower-power rating.

Given the performance uncertainty and potential for harm to some equipment that the MSW product might bring, and the modest power needed, it seemed sensible to select the PSW variant. A 300W product was chosen, partly limited by cost, but also since it is recommended to ‘match’ the power rating to the consumption requirements; in practice the inverter size should be around 3-7 times the power needed by the load appliance. A much higher-than needed inverter is ultimately less efficient for smaller loads, consuming more power than necessary.


Additional parts required were cabling and mounting accessories, plus some optional ‘add-ons’ in the form of other battery chargers and lights to make full use of the generated power:

System accessories

Accessories – MC-4 Connectors & Cable, Light, Battery Charger, Fuses and holder

  • An extension cable to connect the solar panel to the solar controller. The panel itself comes with about 1m of ‘tails’, fitted with MC-4 connectors which are standard for solar equipment. A ‘male’ connector provides the positive supply, and a ‘female’ connector offers the return negative connection. Two cables are therefore required, with the appropriate MC-4 connectors at one end, and unterminated at the other to connect to the solar controller. A ‘top tip’ is to obtain a single fully-terminated extension cable of twice the required length, and cut the cable half-way. For this project, a 25m extension cable was sourced, which provided 12.5m as a sufficient length for both positive and negative connections once cut in half. Thickness of the cable is an important consideration, so that the rating is sufficient for the power of the system and the loss due to the length of the connection. For this installation, a 4mm2 (12AWG) cable was selected, suitable for up to around 15m and 23A, meeting the needs.
  • Battery terminal leads
  • Midi and Blade Fuses and holders for fusing of the output from the battery supply (40A) and protecting the input to the charger controller (15A). The inverter came with a 35A mini-blade input fuse.
  • Lugs and wire for the Solar supply and DC power connections
  • Fixing screws for the solar panel, and cable clips
  • 12V Lamp with remote and motion sensor, providing a light powered by the solar energy for the indoor work area
  • AA / AAA / C / D / PP3 battery charger, for supplementary battery charging requirements, fed from the 12V output from the charge controller (avoiding unnecessary 240V conversion)

The resultant assembly captures energy from the sun via the solar panel, ‘conditioned’ by the controller (to avoid over-charging or issues with varying power) and stored in the battery. Naturally, this can take place throughout the day when the sun shines, without the need for a load to be present. Then when required, the load can be supplied from the stored energy.

The inverter is utilised to supply a replacement AC feed to the specialised Li-ion charger required for the load battery, which can therefore be used as an ‘off-grid’ power source for other uses in place of a regular ‘mains’ supply.

Charging additional Li-ion or Ni-Cad batteries for other equipment can be also be facilitated using the 12V output to supply an appropriate battery charger, and as well as powering 12V LED lights for illumination of the work space.

Hopefully this project is of interest and of use to anyone contemplating establishing a solar energy system, with the aim of harvesting energy from the sun, a ‘free’ resource available to us all!

@YellowsBestLtd our mission is in “Keeping Customers Operational”. We’re always keen to enhance our range of #business services, widen our #enterprise infrastructure support  and expand our mix of #sustainable solutions we offer for supply and maintenance of new and legacy #technologies and products for our customers.

Please help us understand what would be of interest to you by getting in touch to discuss your management services or solutions requirements, whether you’re implementing new systems or maintaining existing infrastructure to serve your operational business needs. We look forward to hearing from you.

Legacy Computing – Windows through time

DOS Beginnings – the early days of ‘personal computing’

The ‘Personal Computer’ (PC) launched by IBM in 1981 was a breakthrough that revolutionised the workplace, though the early ones were quite limited especially in terms of how to use them and what they displayed. Not only did they have no ‘touch screens’ for ‘swiping’ and ‘apps’ as we know them now, but there was no ‘graphical user interface’ either. Rather than a ‘desktop’ with icons and a mouse pointer, there was just a black screen with text and a flashing cursor.


This was Microsoft DOS (Disk Operating System), which seemed to be the ‘proper’ way to use computers for at least a decade.

GEM - Atari ST
GEM – Atari ST

Indeed, some PC users were initially ‘suspicious’ of icons and windows which had appeared on the Apple Mac as well as other alternatives in use like GEM on the Atari ST.

People had become so used to typing commands, and knew all the ‘switches’ and other modifiers e.g. DIR /W to display a list of the files across the screen rather than in a column. And ‘WP’ was all you needed to get ‘Word Perfect’ to launch – the then favoured Word Processor, which gave rise to some still familiar short-cuts like ‘Control-C’ to copy.

Desktop computing takes-off and ‘Windows’ takes-over

Windows 3.1
Windows 3.1

Windows 3.1 showed PC users something different from around 1992, when 386 and 486 PCs powerful enough to run it well became available.

mouse tutorial
mouse tutorial

It even came with a tutorial to show users how to use a mouse!

Windows 3.1 floppy disks
Windows 3.1 floppy disks

No-one enjoyed having to install it using 7 floppy disks though.

And at first it seemed somewhat unnecessary to run existing applications.

Windows 95 – DOS prompt

Indeed, there was a bit of an ‘outcry’  that Windows 95 and later variants didn’t first boot into DOS!

But then it was realised there were some key benefits. Now you could delete a whole directory in one go without having to clear out each ‘level’ – not always the safest feature! Email really became more useable when you didn’t have to log in specifically to check to see if you had messages; now it could be running all the time in its own window.

The rise of the Internet – and security issues

Windows 98 ‘desktop’

With each variant of ‘Windows’ came more sophistication, and suddenly a whole world of connected information could be accessed with Netscape and then Internet Explorer, which then meant Windows really became a ‘must have’.

Internet Explorer - WinXP
Internet Explorer – Windows XP

Certain difficulties were experienced getting old and new applications to behave themselves in the Windows environment; stability and also backwards compatibility started to become issues. Users now had to deal with ‘blue screen’ crashes of Windows, and then a variety of increasing security threats and viruses requiring ever-more enhanced anti-malware protection applications and mandatory backups.

The continuing need for ‘Legacy’ support

Although the majority of modern offices, educational establishments and homes now use the latest PC hardware as well as phone and tablet computing devices running the newest generation of operating software and applications, some industrial workplaces have professional implementations of systems that still make use of early computing platforms (ranging from desktop PCs to OSS servers), where the basic requirements are unchanged, and particularly in stand-alone use where security threats aren’t an issue. And some people still have old PC games to play!

Drive Setup
Drive Setup

It can however be quite a task to restore the operation of legacy systems, particularly if backups are missing or incomplete.

FDISK for partitioning
FDISK for partitioning

Associated issues include obtaining the appropriate hardware replacement parts such as disks (modern versions can be too high capacity to work well with old systems) requiring the right settings of cylinders, heads and sectors, and preparation using FDISK and FORMAT commands.

Floppy Disk
Floppy Disk

Software ‘patching’ of configurations may be needed, hunting out correct versions of driver files and specifying the right parameters. Creating a floppy disk with ‘boot’ files can also be a helpful tool!

Emulation and Virtualisation

There’s still a way today to run legacy software even without the old PC hardware, and that’s via the ‘joy’ of emulation and virtualisation. Even using an Apple Mac or Linux computer, it’s possible to run various flavours of Windows legacy software.

Particularly useful applications to enable this include:


DOSBox – a handy emulator tool which enables the running of old DOS based applications in an application window. Relatively straight-forward to setup, with the ability to ‘mount’ folders so that files can be imported.


VirtualBox – a fully featured virtualisation tool that allows the creation of ‘virtual machines’ into which can be installed a full operating system, such as Windows 3.1, Windows 95 or Windows XP. The tool also emulates CD and Floppy drives for  loading disk images and running legacy applications.

CPU fix for Win95
CPU fix for Win95

Takes a bit of work to set up, preparing a virtual ‘hard disk’, and then installing the operating system. There’s a ‘work-around’ needed to take account of modern processors being ‘too fast’ for the old operating software! Also, to set the display to the necessary resolution and get sound working, special video and audio drivers may need to be installed.



Or you could try the Windows 95 ‘computer as an’ App created by Felix Rieseberg, which can be downloaded and installed on macOS, Windows and Linux!


@YellowsBestLtd we can assist with support services for both legacy and new software and hardware solutions, so please get in touch if you have any requirements you’d like to discuss;  we look forward to hearing from you.

Legacy mobile phones

The original ‘smartphone’ – Nokia Communicator

Remember way back in the late 90’s and early 2000s, when Nokia ruled the mobile phone market, they launched the Communicator series. Essentially it was the coming together of a mobile phone and a PDA, joined with a hinge that ‘opened up’ to reveal a full QWERTY keyboard and display screen. Always somewhat big and bulky, it initially was way ahead of anything else, offering phone, text, email and even fax communication.

Nokia E90 Communicator

The E90 was the last and most feature-packed variant, produced in 2008. More compact and powerful, it featured colour screens inside and out, video and photo cameras with flash, 3G telephony, Bluetooth and WiFi connectivity, together with internet browsing, GPS maps, photos, video and music players, radio, clock, calendar, contacts and a file manager, plus games and the ability to install apps like quick office for document creation and spreadsheeting. In short, it had everything we’ve come to expect in a ‘smartphone’, lacking one key ingredient – a ‘touch’ screen.

Nokia E90
Nokia E90 (closed)

10 years on, it’s a testament to Nokia’s impressive build quality that it looks almost as good as new and still works as well as it did, though of course without the ability to pinch, zoom and swipe, and no ‘app store’. The photo and video quality now looks very basic, as do the limited number of games and apps; but it is possible to load it up with an up-to-date Opera web-browser and Google maps. The music player still works well, using a headset or in speaker mode, as does email and texts – and naturally it can still make telephone calls!

Nokia E90 Communicator
The original ‘smartphone’ – Nokia Communicator

The Nokia phone business itself didn’t fair so well, being eclipsed by the competition and then sold off, as recently well documented in “The rise and Fall of Nokia” (shown previously on BBC4, now on youtube) by Arto Koskinen. However, more recently Nokia phones have made a bit of a comeback, relaunched by HMD Global. Though probably no hope of a new Communicator model?!

Mobile phones for all – Nokia 5110 ‘featurephone’

If you can remember the 20th Century and the dawn of the mobile phone, then the Nokia 5110 maybe familiar. Introduced in 1998, during the period of Nokia’s seemingly unstoppable rise, and helped them become the world’s number one mobile phone producer, which they remained for the next 14 years.

Nokia 5110
‘Featurephone’ for all – Nokia 5110

This was the breakthrough when phones ceased to be ‘bricks’ (though still including an external antenna) and became mass-market devices that everyone could consider carrying, even just as an ‘emergency’ phone. Text messaging was included, though many people at the time couldn’t see what the point of that was: “its easier to just ring someone, isn’t it?” How times have changed! Plus it had a clock, calculator, and a choice of ring tones including the now famous ‘Nokia tune’. And Nokia introduced the world to ‘snake’, heralding in the era of mobile gaming. No app store yet, and ‘touch screens’ and even colour displays were still to come. But you could now choose the colour of the product; they didn’t have to be just black anymore!

'snake' game
Nokia 5110 – ‘snake’ game

The phones themselves were of the solid long-lasting construction that characterised the products of that time from the Finnish manufacturer, perhaps due to the harsh winter environment of home they were built to survive, which is why 20 years later, it still works! Looking back, the surprising thing is that despite its rugged nature, a case was often used, and given the (now, seemingly) impressive talk and standby time, it was quite usual to have a spare battery too. Perhaps that was because they were still seen as an expensive luxury, and given that ‘normal’ desk phones didn’t run out of power, ‘early adopters’ wanted to make sure they could always make use of their investment.

Legacy 'Featurephone'
Nokia 5110 with accessories

Much has since changed in the world of mobiles, such that they’re not even used much as just ‘phones’, and Nokia’s phone business itself came and went, though now being revived by HMD Global. On the cusp of the launch of a new ‘flagship’ model, the Nokia 6.1 plus, it’s also interesting to see the ‘re-introduction’ of some ‘classic’ phones, the 8110 and 3310, harking back to those early beginnings.

@YellowsBestLtd we’re always keen to hear from #business customers looking to maintain and keep operational “legacy” products and #enterprise equipment, as well as newer #systems, helping to source and supply spares, repair and support services so that assets and #technologies continue to serve and perform. Please get in touch to discuss your Management Services and Solutions requirements; we look forward to hearing from you.

Keeping Customers Operational – ‘telling’ not ‘selling’

@YellowsBestLtd our mission is to provide our Customers with Management Services and Solutions so their infrastructure networks continue to serve and perform – “Keeping Customers Operational

Needs vary from the launch of the latest IT and Telecoms technologies through to the support of well-established legacy systems.

Given that each organisation is unique, both in its business practices and deployed infrastructure, then we find that its best to take a flexible approach and provide tailored services to suit exacting demands.

Our no-cost and no-obligation Customer consultation is all about finding out needs, regardless of technology or manufacturer, and then sourcing the required solution(s), which may mean seeking out difficult to obtain products or requiring the supply of specialist services.  So in essence, it’s not about us ‘selling’ them something we have, but rather our clients ‘telling’ us what to provide. Making it easier and more convenient for busy procurement and operational teams,  saving them effort, time and cost.

We’re always keen to see how we can enhance our range of #business services, increase the #enterprise infrastructure we support and expand our mix of #systems solutions to supply the required #technologies and products for our customers.

Please help us understand what services would be of interest to you to  support your systems requirements, by getting in touch; we look forward to hearing from you.

Business Services
Day Rate Operations & Maintenance Engineering Site Visits Hardware Repair
Project Based Training Solutions Sourcing Software Support
Consultancy Telephone Assistance Spares Supply Reverse Logistics & Value Recovery


Enterprise Infrastructure
Alcatel-Lucent Bosch Ernitec Ganz
Huawei IBM Keymile Marconi
Nokia Pelco RAD 360Vision


Sustainable Solutions
Legacy Systems Refurbishment Testing Craft Terminals
Spares Sourcing Repairs Maintenance Technical Support
New Telecoms Infrastructure Functional Replacements Reverse Engineering Management Systems


Technologies & Products
PDH Access SDH Transport IP / MPLS CCTV Cameras
Copper Cabling Microwave Radio Pseudo-wire Solar Energy
IT / Servers DWDM / CWDM Carrier Ethernet PMR / TETRA

Nokia, Marconi and Ericsson SDH – ‘Synfonet’, ‘SMA’ and ‘OMS’

‘Legacy’ Networks; long history, but still important and operational!

Back in the day, when PDH (Plesiochronous Digital Hierarchy) was all there was for telecommunications optical and copper transmission, a familiar site was the ‘Multiplexer Mountain’.

PDH Multiplexer Mountain

Then came the new transport technologies: SDH (Synchoronous Digital Hierarchy) for high-speed digital communication (via optical fibre and radio links); and (D)WDM ((Dense) Wave Division Multiplexing) as an optical solution for raising the capacity of existing fibre networks (particularly when the fibre-count was limited).

Nokia launched the ‘Synfonet’ range as the big brother to their successful ‘Dynanet’ PDH portfolio, with SDH capacity of initially STM-1 (155MBit/s) and STM-4. Later came STM-16 and WDM.

Synfonet – STM-1/4

  • All in one subrack (REG, TM, ADM, DXC)
  • Wide range of tributaries
  • 64kbit/s cross-connection server
  • Upgradable from STM-1 to STM-4 while in service
  • Compact, flexible and easy to expand

Nokia Synfonet

Synfonet – STM-16

  • 2.5 Gbit/s, four times the throughput rate of STM-1/4

Nokia Synfonet

Synfonet – WDM

  • 4–channel multiplexing / demultiplexing
  • 8-channel multiplexing / demultiplexing
  • Up to 20 Gbit/s per fibre

Nokia Synfonet

But in 1999, Marconi Communications acquired (for over $100M) Nokia’s Synfonet brand, SDH and DWDM transport equipment products and about 120 staff from its Cambridge research and development business under the deal.

Inevitably over time Marconi rationalised their portfolio and the Synfonet range was discontinued, in favour of the SMA and MSH SDH equipment.

Business however took a downward path and in 2005 Ericsson acquired the key assets of Marconi (for SEK 16.8 billion). “Marconi” then became the registered trade-mark branding for Ericsson to promote these products, until phasing them out.

Marconi® Series 1 SMA1 Multiplexer

  • Flexible SDH Multiplexer
  • Terminal, Add/drop (ADM) or Digital Cross-Connect (DXC)


Marconi® Series 3 & 4 SMA Multiplexers

  • Full range of options, including size and power variants
  • SMA1, SMA4, SMA16c and SMA16c+ Series 3 models
  • Tributary interfaces from 2MBit/s to STM-4
  • SMA1/4, SMA1/4c, SMA1/4E and SMA1/4UC Series 4 models
  • Supports ATM and IP with enhanced data functionality
  • Metro access and metro core deployment, and customer premises


Marconi® SMA 16-64 Multiplexers

  • Advanced ADM, DXC and low-order aggregator
  • Delivers 2.5GBit/s and 10GBit/s data transport capabilities
  • Full VC-12 granularity allowing single-layer access without VC-4 layer
  • Metro core deployment


Marconi® MSH Series

  • Family of STM Multiplexers, Regenerators and Cross Connects
  • MSH11C, MSH41C, MSH51C, MSH63, MSH64, MSH64C and MSH86 Models.


Marconi® MSH2K

  • Foundation of Marconi’s switching portfolio
  • DXC functionality, capacity of 320GBit/s
  • Support for STM-1 to STM-64 electrical interfaces
  • Embedded DWDM and support of SDH protection / restoration
  • Seamless transition from Ring to Mesh network architectures
  • Capable of upgrade to Multi-Layer Switch (MLS)
  • Metro core deployment


Marconi® MSH64C

  • Based on same platform as MSH2K
  • Core ADM/XC, 80GBit/s switch, capacity of 32 x STM-64 interfaces
  • Consolidating and grooming traffic.
  • Gigabit Ethernet interfaces for data transport
  • Embedded DWDM interfaces


From 2007, Ericsson launched the (still) Marconi® branded OMS (Optical Multi Service) portfolio of advanced SDH multiplexers, including OMS 1200, OMS 1400 and OMS 1600 providing multi-service products for Metro-Edge and Metro networks. The “Marconi” brand was later dropped by Ericsson for this OMS range.

OMS 1200 range

  • Range of SDH ADM
  • Optimised for ring and terminal applications

OMS1200 series

OMS 1400 range

  • Compact energy efficient multiservice and packet optical transport.
  • Optimized for use in Metro Access networks
  • Carrier class Ethernet and TDM services interworking with metro and core Networks based on SDH, Ethernet or IP/MPLS
  • Applications ranging from high capacity customer sites, fixed or mobile backhaul/Radio Access Network (RAN) aggregation and transport


OMS 1600 range

  • Compact, multiservice transport and switching platform
  • Terminal, Add/Drop and Cross-connect multiplexers
  • Line, ring, star and meshed networks
  • Modular configurability, comprehensive switching options
  • High port density reducing space and power consumption
  • Range of data and TDM services, fulfilling ITU- T G.782 requirements

OMS1600 Series

The OMS range provided packet evolution capabilities to Ericsson’s optical networking portfolio and strengthened its Full Service Broadband offering, meeting the demand from operators to evolve their network to support a mix of services and traffic types, with dexterous backhaul connectivity, TDM or Ethernet-based, with telecom quality, flexibility and scalability.

Perhaps this ‘potted history’ helps explain the ’journey’ these products took, and clarifies why they can be referred to as both Nokia and Marconi, or indeed Ericsson. Although now discontinued by these manufacturers, the products are extensively deployed and still in use by Telecoms Operators, Utilities and Transport companies.

Supporting ‘Legacy’ Networks and Keeping Customers Operational

From time-to-time Customers benefit from services from @YellowsBestLtd

  • Locating Nokia, Marconi, Ericsson (and other vendors) hard-to-find replacement items
  • Hardware repair services to existing parts
  • Supplying additional spares for newer systems to increase capacity or provide alternative interfaces

This way these ‘legacy’ but still important networks can continue to be maintained and kept operational.

To illustrate the possible requirements for spares and repairs, some key parts from the above networking technologies are listed, as follows:

Nokia - Synfonet


Part Code Family Description
STM-4 (T30023.01 – 71.02) Synfonet STM-4 card
STM-16 (T30172.02 – .06) Synfonet 2 x STM-1/4 WDM Mux
WDM MUX (T30172.41) Synfonet 2 x STM-1/4 WDM Mux
STM-1 E/140M (T3033.01) Synfonet 140Mbit/s STM-1 electrical IU
34M/45M (T30046.02) Synfonet 34/45Mbit/s electrical IU
2M TA (T30041.01 – 43.01) Synfonet 2Mbit/s interface units
CU (T30073.01) Synfonet Node control and timing unit
SSW (T30053.01) Synfonet System Switch Unit
SU-A (T30084.01) Synfonet Service unit / EOW
SPIU (T30093) Synfonet PSU Card
TSW0 (T30110.01) Synfonet 64 kbit/s cross-connect unit
TSW1 (T30063.01) Synfonet Cross-connect unit for STM-4

Marconi - SMA / MSH


Part Code Family Description
02HAM00002AAJ SMA-1/4 21 X 2M LTU Balanced
02HAM00003AAL SMA-1/4 63 X 2M LTU Unbalanced
03HAT00010AAS SMA-1/4 10/100MB Ethernet Module
1HAM61217AAK SMA-1/4 Power Unit
1HAT 60796 AKU SMA-16 STM-16 OPT.TCM AHK S16.1 (SC)
1HAK 60596 AAE SMA-16 STM-16 RX OPT S16.1
1HAK 60701 ABM SMA-16 STM-16 TX OIC 1310nm (FC/PC)
1HAT 60730 ADL SMA-16 STM-16 LINE UNIT 1550nm (FC/PC)
1HAT 60730 AJX SMA-16 STM-16 LINE UNIT 1310nm (FC/PC)
1HAT 60730 AMA SMA-16 STM-16 L-16.1 SC
1HAT 60730 ANS SMA-16 STM-16 L-16.2/3 SC
SN99AD SMA-16 Power Supply Unit
Part Code Family Description
133-1467/01 MSH86 Matrix Shelf
131-9475/21 MSH64 STM-64 S64.2 SC/PC
131-9475/22 MSH64 STM-64 L/V/U64.2 SC/PC
131-8685/01 MSH11C 3 X 34MBit/s Tributary Unit G.703
133-1260/01 MSH84 MSH86 Shelf Type 5
130-3118/01 MSH84 Trib Matrix Board
130-3132/01 MSH84 Control Matrix Sub Unit
130-3142/01 MSH84 Main Control Sub Unit
1MBD60697AAT MSH2K Shelf
02MBB00001ABG MSH2K S-16.1 Module, LC
02MBB00001ACY MSH2K L-16.1 Module, LC
02MBB00001ADR MSH2K L-16.2 Module, LC

Ericsson – OMS


Part Code Family Description
03HAG00001AAX OMS1200 A/D Mux System Chassis
03HAM0019AAQ OMS1200 HI Power DC Supply
03HAN00007AAH OMS1200 AC Power & Battery Backup
03HAN00009AAM OMS1200 Fan Unit
03HAT00041AAQ OMS1200 Common Control ADM Unit-A
03HAT00041ABH OMS1200 Common Control ADM Unit-B
03HAT00045ABR OMS1200 Ethernet Prnt Card
1HAT61107ABC OMS1200 64 x 2M Core Trib Card
1HBA60828AAX OMS1200 32x 2M Unbalanced LTU
1HBA60832AAA OMS1200 32x 2M Balanced LTU
1HAT61106BAE OMS1200 Comm/Aux/ANC Unit
1HAM61217ABC OMS1200 Power LTU Mod
Part Code Family Description
03HA500032AAC OMS1664 STM-1 Switch Card
03HAM00006AAT OMS1664 STM-1 Line Terminating Card
03HAM00015AAG OMS1664 10/100 Electrical LTU-Type 2 (SK57BC)
03HAT00015AAD OMS1664 STM-4 Line Card
03HAT00016AAF OMS1664 STM-4/16 Core Card
03HAT00021AAK OMS1664 STM-16 Line Card
03HAT00020AAH OMS1664 STM-64 Line Card
03HAT00029ACM OMS1664 16xE1
03HAT00053AAK OMS1664 140M Transmux Card
03HAT00057ABL OMS1664 Ethernet L2 Data Switch Prnt Card
03HAT00054AAM OMS1664 Ethernet Layer 2 (8+16 Ports) (SK58AB)
1HAG60619AAK OMS1664 Standard Shelf
1HAG60620AAF OMS1664 Compact Shelf

Please get in touch and let us know what you need to keep your network in good shape!

Business Financing

Equipment Leasing and Funding

With Business expansion in mind, when there’s a need to fund key purchases of equipment, but you don’t want to tie up precious capital, and perhaps even with a carefully worked out business plan, your bank won’t provide the lending – help, is at hand …

@YellowsBestLtd we can assist with funding though our business finance partners. Finance can be arranged for nearly all business equipment, machinery and IT (including software). With facilities small and large that can be repaid over 1 to 5 years, it makes sense consider how you can get what you need now, not what you can only afford. After all, you don’t pay for your staff 3 years in advance, and you don’t wait to buy a building for them to work in. So don’t hold yourself back!

Please get in touch to let us know what you need to purchase and see how we can enable your business to move forward. Or perhaps you’re selling your products to your Customers, in which case we can arrange a point of sale facility to aid their purchase and accelerate your sale.

Summary of Customer Benefits

– an alternative line of credit: finance lease, lease/hire purchase, loans, sale & leaseback

– tax efficient: leasing is 100% tax deductible

– all asset types considered: office equipment, production machinery, fixtures & fittings, etc

– the biggest benefit is ‘the use’, not ‘the ownership’

Summary of Vendor Benefits

– provision of ‘point of sale’ leasing and finance facilities

– increase order values, sell more equipment

– incorporate services & consumables in rentals

– more effective cost justification

“TESTERS” – Test Equipment to suit all deployed technologies

Customers who own infrastructure systems usually require some form of test equipment to assist with the build, operation and maintenance activities.

Given the mixture of old and new technologies now deployed, consequently the range of available test equipment options has grown considerably. And like the infrastructure systems themselves, new functionality demands and obsolescence issues also affect the associated test equipment needs and availability.

@YellowsBestLtd assists Customers by sourcing the required test equipment, supplying either modern or legacy units. Often refurbished ex-hire equipment in excellent condition and at commercially attractive prices makes sense over leasing. This ensures the continued availability of sets of the appropriate specification, which may become discontinued by the manufacturers over time.

If necessary, we can also arrange the repair of existing units, especially those that perform very specific functions that cannot easily be replicated with more recent equipment.

There follows a brief description of many of the types of test equipment available; we would be very keen to hear from you to understand your specific requirements, so please get in touch!

Calibration Checkboxes

Calibration checkboxes, or electrical checkboxes, are used for routine observations of test equipment and allow users to maintain accuracy in between official calibration procedures. Suitable for use with PAT testers and with other testers and instruments.

Calibration Checkbox
Calibration Checkbox

Component Analysers

These test the efficiency and status of components including transistors and capacitors. An essential instrument for development engineering when specific components are used in product design.

Component Analyser
Component Analyser

Earth Loop Testers

Loop impedance testers, or loop testers, verify the loop impedance of a live electrical circuit without disconnecting from the electrical supply. Most testers include non-tripping RCD technology as standard to prevent unexpected outages.

Earth Loop Tester
Earth Loop Tester

Earth Testers

These verify that electrical current paths are safely earthed. Earth spike testers, high current loop testers with earth stakes and leads are available.

Earth Tester
Earth Tester

EMF Meters

EMF meters are used for verifying the presence of electrical magnetic fields given off by electrical equipment. Ideal for use in heavy-duty electrical applications and laboratory testing conditions.

EMF Meter
EMF Meter

EVSE Testers

EVSE testers are purpose-built for the installation, testing and maintenance of electrical vehicle supply equipment and are an essential for use by electrical vehicle charging point installers, manufacturers and anyone else involved with EVSE equipment.

EVSE Tester
EVSE Tester

Insulation & Continuity Testers

A wide range of insulation and continuity testing instruments which include Megger insulation testers, insulation resistance testers, Fluke testers and insulation meters from Amprobe, DiLog, Seaward, Metrel, Martindale, Kewtech and Extech.

Insulation and Continuity Tester
Insulation and Continuity Tester

LCR Meters

LCR meters get their name from their testing capabilities – they can test inductance (L), capacitance (C) and resistance (R).

LCR Meter
LCR Meter

Multifunction Testers

Ideal for use when completing or testing an electrical installation. The huge range of MFTs include the Fluke 1600 range and Megger installation testers.

Multifunction Tester
Multifunction Tester

Optical Fibre Inspectors

Quickly find and inspect the right port. Like having a built in flash-light so you can see in dark areas and dense panels. Pause button holds the image for viewing when it’s hard to get it just right. Bright backlit display. Screw-on probe tips to support most connector types.

Optial Fibre Inspectors
Optial Fibre Inspectors

Optical Fibre Visual Fault Locators

Locates fibres, finds faults, verifies continuity and polarity. Locates visual faults including tight bends, breaks and bad connectors. Easily verifies polarity and identifies fibres. Features continuous and flashing modes.

Optical Fibre Visual Fault Locator
Optical Fibre Visual Fault Locator

Optical Power Meters

Multimode and Singlemode Power and Loss Measurements. Multiple kit configurations with light sources for single mode, multimode and PON fibre optics. Min/Max capability automates tracking of intermittent power fluctuations.

Optical Power Meter
Optical Power Meter

PAT Testers

For Portable Appliance Testing (PAT) routine safety checking of electrical equipment, including dual insulation test voltages and portable RCD lead testing, with adjustable PASS testing limits and substitute/mains powered leakage testing procedures.

PAT Tester
PAT Tester

Power Quality Analysers

These provide a comprehensive snapshot of how power is being used in your facility and verify where energy is being lost. The latest power analysers and power analysis tools include those from Fluke and Hioki.

Power Quality Analyser
Power Quality Analyser

Production Line Safety Testers

Perfect for laboratories and product design applications, the equipment in this category can be used to verify electrical safety, service equipment using multiple electrical parameters and to simulate PAT conditions.

Production Line Safety Tester
Production Line Safety Tester

Proving Units

An essential accompaniment to a voltage tester, proving units verify that the tester remains accurate both before and after testing. Both the NICEIC and NAPIT strongly recommend using these regularly when testing.

Proving Unit
Proving Unit

RCD Testers

For testing RCD trip time and overall residual current device safety/efficiency. Available are handheld RCD testers, Megger RCD testers, RCD analysers and multifunctional RCD testers which also measure loop and PSC.

RCD Tester
RCD Tester

Socket Testers

These testers are placed into a socket to assess faults with the wiring using audio/visual feedback.

Socket Tester
Socket Tester

Telecom Datacom Analysers

Ideally suiting traditional telecommunications networking requirements, typically providing testing at V.24, V.35, V.11/X.21 interfaces at rates up to 2 Mb/s.  Also a full range of BER/BLER measurements, control-circuit timing analysis with transitions diagrams and storage in text and graphic form.

Telecom Datacom Tester
Telecom Datacom Tester

Voltage Testers

Voltage Testers

These verify the presence of voltage, and allow full test of voltage levels. Instruments are available from the leading test equipment manufacturers such as Fluke, Kewtech, Martindale, Amprobe and Megger.

Voltage Tester
Voltage Tester