NODE | Radical Tech Tutorials

#134 Making a better Allstar Node

While looking for solutions to connect to my radio clubs repeater systems. I considered a few solutions, eventually I settled on the Allstar asterisk system. This allowed us to connect analog radio signals over the internet similar to traditional repeaters without sounding too much like a VOIP system.

The system was created by a ham for hams with lots of settings and capabilities as well as tons of customization options. This sounds complicated but it doesn’t have to be. The beauty of the system is that you can decide to just buy a node or voter or make your own hardware. There’s options to cater to a large range of ham operators, there’s even commercial licensing (asterisk) and systems for business operators which is also nice. Having options is always good in a robust communication network.

Pogo pins for data with a choke to filter the data lines

After making a few DIY nodes I wanted to make my own complete professional PCB node unit with quite a few requirements.

Namely:

0805 parts.
Affordable and efficient as possible but also prototype friendly.
Easy layout for quick soldering.
Extra fuses and protection.
Reverse polarity protection USB-C.
Built in battery (LiPo pillow cells) commonly available & large capacity.
Short or limited no (wires flopping around)
Good grounding.
Good 50v or 35v capacitors.
Calculate PCB thickness/shielding and filtering for 50ohm impedance.
Solder bridge points and lots of headers for testing and debugging.
Antenna fits in a monopole way so try have decent ground plane.
Built in efficient linear charging circuit (avoid noise as much as possible)
Power path circuitry to allow charge and power (need good wall adapter)
Built in step up to 5v high current for PI and radio.
5v step up converter with high efficient and frequency (min 500khz)
Use Raspberry PI zero 2W hat approach
Pogo pins for USB data & choke
CH340 type of UART to TTL IC for programming SA818.
USB differential pair tuning.
4v linear regulator for filtering before powering radio module.
Uses SA818 modules (UHF/VHF FM capability)
Ability to connect any radio if needed (so not forced to use the SA818 module)
Proper radio filtering for UHF/VHF FM options.

After taking all these points into consideration I was able to do a bit of research and just a tiny bit of testing and then some more testing and then some more… Finally I was happy with the PCB I had sourced a decent box and design concept and all the parts allocated. I calculated all the costs at time of purchase and manufacture and sent to Gerbers off.

A few weeks later I was greeted with some decently manufactured PCBs.

On fitting the actual PCB to my enclosure I noticed the edges needed to have a more aggressive chamfer… Which I was able to do manually with a metal file tool. I did this outside with eye protection and a proper mask with respiratory particle filter. FR-4 carbon fiber dust in no joke.

After about a year of testing and playing around with different configurations I’m quite happy that this project worked out really well.

The two biggest concerns are chip availability and time designing, researching and developing.

Creating a commercial version of any project or product has a few other challenges, the big one being “bureaucracy” sadly there’s not much that can be done and “the process” can never be trusted.. we can only suffer through it and hope to be a better person at the end of the day.

Video demonstration here.

#126 Creating An Allstar Node

Display prototype on an actual Bread Board 🙂

In my previous article I was focused on the RTCM and the VOTER PCB which are used with repeaters. however I found out you could make a node instead for personal use. So basically a node is a radio connected through a sound card to a raspberry pi acting as an Allstar server.

You setup and connect this to the internet and you have a home made personal gateway to the Allstar servers. now you can listen or chat with anyone on the Allstar network

With that being said I was very interested in making my own version but I wanted it to use LiPo battery power for portability and a solar panel as power intake. I wanted a complete stand alone unit that could be setup once and placed somewhere and almost forgotten just remembered for maintenance and check ups.

I also wanted clean audio which could be a whole article in itself but for this write up I’ll be brief.

Testing out different filters and super capacitors

Eventually settled on a case with very short wires

I got the initial setup working using a UHF only Analog radio connected to a CM108 sound card that is plugged into a raspberry pi 2w with an OTG adapter. (it’s very important to keep all the wires as short as possible to prevent them from becoming antennas!!)
This was connected to a 5V step up converter and charger in 1 module. Now the radio needs max around 4.2V so I had to add an additional stepdown converter to accommodate this.

Everyting worked well and the system was portable but there was a very annoying whine. with some filtering I was able to reduce this significantly and the setup was almost done.

One annoying issue was that when the 5vstep up converter switched from main to battery power there was a very brief short delay where power to the raspberry pi could be lost casing a brownout and reboot of the pi. The solution was to add super capacitors in parallel with the supply to keep the volts flowing during this dip in power.

Also using a linear voltage regulator with a high ripple rejection circuit helped reduce the audio whine and noise

Over all this was a fun success of a project I will be creating a permanent case for my DIY version and I will be creating my own custom Nodes with a professional PCB for sale in future!

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