Allstar Link Node Build - Part 6

Welcome to part 6 of my Allstar Link node build. 

In this instalment the project finally comes together with the boxing up of all the various modules and parts that I covered in my previous blog posts.
 

Choice of enclosure

To enclose the project, I decided that I wanted to keep everything screened to minimize the possibility of unwanted interference in the shack. You may remember in part 4 of my build I commented that there's a reason computers are built into metal boxes!

I suspect that some readers of the blog maybe thinking but "my laptop case is plastic";  therefore my comment or argument is not a valid one! 

 

Well, having stripped down many laptops for repair, I can substantiate my point due to the fact that the internal electronics of a laptop are shielded either by tin sheeting or a screened coating on the inside of the plastic shell, the same can also be said for tablet computers and mobile phones.

The enclosure I chose is a split body extruded aluminium type, as shown below.

The dimensions of the case are 54 by 145 by150mm. I purchased mine from eBay and paid just under £15 for it delivered.

If the above web links are no longer valid just search on Google with the following "Aluminum Enclosure 54x145x150mm" and you should find a few suppliers listed.

Options for high or low RF output power

Before proceeding any further, a decision needs to be made regarding what the final RF output power from the node will be. By default the radio is capable of producing around 4 watts of RF output. Taking into account that the node will operate with a high transmit duty cycle, it is necessary to reduce the RF output to a safer level to avoid damage.

Option 1: For low power 20 to 40 mW you do not need to fit the Buck Converter module or drill the associated mounting holes; however, a further modification must be made to the Baofeng BF888 to reduce the RF output to a lower level. The modification involves the removal of the main RF output transistor, this is then bypassed using a capacitor or wire link.  For further information on this modification please take a look at the following web link:  888 Low Power Modification

Option 2: For high power 100mW or above, you will need to fit the Buck Converter module and drill the associated mounting holes.

For now I will continue with the casing up based on using option 2.  I will cover the transmit output power in more detail later once everything is mounted in the enclosure and wired up.

Template for drilling the bottom of the case

All of the main electronics are mounted on one half of the case and from now on, I will refer to it as the base.

I produced a drilling template for the base in CorelDRAW; this allows me to replicate the drilling process and share my layout as an aid for other node builders.

Below is an image of the template I created but please note it is not to size.

 

Click to enlarge to full size!

If you want to print a template from the above image, click it so it displays full size,  then save it to your computer and use your favourite graphics programme to print a copy out.  The file is a standard PNG type and should be printed at 100% size, resulting in an image that is 129mm by 150mm. If you would like a copy of the template in PDF format, please message me using the contact form at the top of the web page.

Cut out the template and make sure it sits flat at the bottom of the case as per the illustration below.

If the template fits correctly, there should be no side play movement. To avoid the template sliding in a front to back direction, secure it in place with Sellotape or masking tape along the front and back edges.  I recommend that you use a centre punch to make shallow indentations in the aluminium and remove the template prior to drilling.

Drill the fixing holes as per the template and your preferred RF power option. Start off with a small 1-mm-drill bit and increase the drill bit size gradually to get the needed hole sizes. The drilled base (option 2) should look like the one in the image below.

Mounting the modules

For mounting the modules, you will need some PCB standoffs.

8 of M3 thread type - female to female - 8 to 10mm in length

2 of M2.5 thread type - female to female - 8 to 10mm in length

I used brass types but you could also use the steel nickel-plated variety; I would, however, avoid using the nylon nonconductive type, as these could cause issues with PCB grounding.

The two M2.5 PCB standoffs were used on the LM317 module and the M3 size on the rest of the modules.

Offer the PCB standoffs to the respective module mounting holes and check to see if the standoffs have clearance from nearby PCB tracks or components,  if needed, use insulating washers between the standoffs and module mounting holes.

All the modules in place

Here is an image showing all of the modules in place,  securely mounted and ready for wiring up.  Note the USB sound module is not shown in this image; it simply plugs into one of the Raspberry PI USB ports.

Wiring the Modules

Connect the red, orange and black wires from the Baofeng radio to the modules as illustrated in the next image. Next fit additional wire links between the buck converter module and the LM317 voltage regulator module. If you prepared the radio with different coloured cables to the ones used in my example, care should be taken to ensure the cables are connected to the correct points!

If you have opted to build the low-power version of the node and omitted the buck converter module wire as follows. 

Here is an image of all the modules mounted to the base of the enclosure and wired up ready. Note the CM108 sound module is plugged into the bottom USB port (top left in the image). It is then secured in place with an end stop made from 1.5mm thick angled aluminium size 20mm by 20mm. Use the two remaining holes in the base of the enclosure to mark up the angled aluminium ready for drilling. Drill the holes with a 3-mm-drill bit and secure in place with M3 fixings.

Front Panel

I produced a front panel label in CorelDRAW then printed it onto photo quality paper  with my inkjet printer.

Below is an image of the label I created with the enclosure front panel.

 

 

The label is used as a template to mark the drill holes prior to drilling. Once all the holes are drilled, the 4 corner screw holes on the label must be cut out carefully with a small sharp craft knife. This is a tricky job, as the holes are close to the edge of the paper.

The label is fixed to the front panel using "3M Spray on Display Mount Adhesive" available from the likes of Amazon & eBay.  Allow sufficient time for the adhesive to dry then trim out the holes for the LEDs and switches.

Here is an image of the front panel with the label fixed in place and the LEDs and switches mounted. The text placement under the switches could do with lowering a little but I am otherwise happy with the end result.

If you would like a printable copy of the front panel with your callsign on please message me using the contact form at the top of the web page and I will send you a copy via email in PDF format.

Wiring the front panel

Using the diagram below, wire up the front panel controls and LEDs. Care should be taken to ensure the cables are connected to the correct points, especially if you have used different coloured cables to me!

NOTE The wiring points shown are correct for the Raspberry PI 3B plus model, if you are using an earlier or later model of the PI, the connections may be different!

Wiring the antenna socket

I decided to re-use the original rubber duck antenna and socket from the Baofeng BF888. The socket is mounted on the top half of the enclosure using a 150mm length of RG316 coax cable.  Here is a picture of the cable soldered to the socket and the free end prepared ready for connection to the radio.

 

Before the coax cable can be attached to the radio, a small amount of the green solder mask must be removed from the PCB close to the antenna connection point to forms a ground connection point.  

The following image shows the coax cable soldered in place on the radio.

Back panel

Before the wiring can be completed, the enclosure back panel needs to be prepared with holes cut for the DC power and ethernet network socket.

I have produced a template for the back panel in CorelDRAW. Click the image below to make it full size, then save it and print to 100% size.

Click To Enlarge Full Size!

The square hole for the network socket can be formed by drilling a series of holes to remove most of the unwanted aluminium then finishing it off with a small file.

The network socket/extension cable that I used is branded iGreely and is 1ft/30cm in length. They are supplied in a pack of 2 and are available from Amazon at the following web link  

https://www.amazon.co.uk/iGreely-Female-Ethernet-Network-Extension/dp/B06Y4J9MZ4/

If you carry out a search on Google with the text "iGreely 2Pack RJ45 Male to Female Screw Panel Mount" you will find lots of suppliers for the cable.

Remaining Wiring

To complete the wiring connect the remaining power supply cables, as shown in the diagram below.

NOTE The wiring points shown are correct for the Raspberry PI 3B Plus model, if you are using an earlier or later model of the PI the connections may be different!

I also soldered an additional ground wire from one of the Raspberry PI USB connectors to the Baofeng radio, as can be seen on the next image.

Setting the regulator voltages

Before the top enclosure cover can be put in place, the voltages must be set on the buck converter and LM317 modules.  

My node build is designed to run off 5 Volts DC and as I mentioned previously, I will be using a conservatively rated Raspberry PI 4 power supply to do the job. The PI 4 PSU is fitted with a USB C plug, this must be chopped off and replaced with a 2.1mm DC power plug.

***** IMPORTANT *****

Before applying DC power to the node for the first time, you must ensure that the Baofeng radio is turned off. This step is necessary whilst the buck converter & LM317 modules are adjusted and set to the correct output voltages.

Using the illustration below power up the node and adjust the module output voltages.

Once the voltages have been set, switch on the Baofeng radio and check the voltages again and make any fine adjustments if necessary.

Adding a protection fuse

Following my concerns regarding the buck converter module, the fake LM2596 and the prospect of it failing short circuit I decided to add a protection fuse. To do this, I cut a small strip of FR4 strip board with a break in the copper PCB track that is bridged with either an SMD or wire ended PTC fuse. The PCB is conveniently soldered to the- on/off toggle switch and if the fuse should trip power is isolated from the node.

The image below illustrates how I implemented the inclusion of a protection fuse. 

The rating of the fuse will depend on the overall current drawn from the node during transmit mode. For now I have fitted a wire link while I wait for fuses to be delivered.

Adjustable The Baofeng BF888S RF output.

In Part 2 of my node build blog, I covered preparing the Baofeng radio and adding various cables.  Referring back to that blog post, there is a section headed "Secondary power supply input" and another "A clean break". The information outlined forms what I can now reveal as my "adjustable RF output modification".

The break I cut in the PCB track isolates the transmit driver and output stages from the main radio's power supply rail.  The additional secondary power supply input (orange cable) provides an independent supply point for the transmit driver and output stages.

The buck converter is used solely to supply voltage to the Baofeng radio's transmit amplifiers. The variable voltage, in essence, provides a means to adjust the RF output level from the radio.

The Baofeng 888's RF output stage appears to run in class AB mode and not class C as I expected. This gave me some cause for concern, as any alteration to the supply voltage would inevitably change the transistor biasing.  In testing my concerns were unfounded and I was able to adjust the RF output down to a couple of hundred milliwatts and the monitored audio sounded clean and distortion free.

With the buck converter set to 1.6 volts, the RF output from the radio is approximately 500mW. When transmitting the duty cycle of the node can be very high so I would recommend that the RF output from the radio is not set too high.  Check your amateur radio licence conditions to ensure that the node is operated in compliance!

Final preparations

Before the top cover is put in place, a hole must be drilled to mount the antenna socket; also a micro SD memory card with software must be prepared for the Raspberry PI. 

The image below shows you a completed node and illustrates the placement of the antenna socket. Apologies for the poor quality of this image :)

The software I recommend for the node is produced by David McGough - KB4FXC. It is available as a free download from the Hamvoip Website.

Click here to go to the HamVoip website

I am not going to cover the installation and configuration of the software on the blog, as that is well documented on the HamVoip website but once you have taken care of the software side, your node will be operational and you can start having some fun!

EndNote

Please note that the status LED will not be functioning correctly yet. If I am able to resolve this I will do a follow up blog post to cover this.

If anyone can provide me details or scripts to get the status LED functioning correctly please contact me using the form at the top of this page.

The project is all but complete and I hope my build notes provide some inspiration and can serve as a useful guide to help other hams who may be interested in building an Allstar Link Node.

Until next time... 

73's From Andy G6LBQ

Its all about the Radio Ga Ga...