Tag Archives: HAM RADIO

DUAL BAND ANTENNA FIX

14 August 2025 Cale Leave a comment

#127 Fixing a Faulty Handheld Antenna

A while ago I purchased a few hand held radio antennas from a reputable source. Unfortunately one of them had a great SWR for 2m but a terrible SWR for 70cm. So I began investigating this and started to take apart the antenna to find out more. Just as a side note: I would not recommend this for beginners or businesses (if you have a faulty product immediately contact the seller and get a replacement or refund)

So during my autopsy of the antenna I was able to determine a few things. Firstly the plastic connectors in the middle of the antenna is supposed to have a loaded coil but there was just a crimped thinner antenna wire. Second on opening up the base of the antenna I was surprised to find out that they had a metal enclosing case which was nice.

Then looking at the SMA connection to the antenna I was pleased to see a base tunning coil and capacitor, this is a good sign. potentially meaning the antenna is a “GOOD COPY” of whatever the original antenna was. the antenna has zero markings but we can take a guess that its a good copy of the Diamond RH951

Finally I found the culprit.. the capacitor on the coil seemed to be destroyed.. after de-soldering it and testing it turned out to be a faulty part. So in order to fix the antenna I soldered another cap with a close enough value.. (13pf instead of 12pf) and sure enough after putting everything back together a gluing it the antenna worked perfectly but did have a slight frequency shift when Compared to the others I had purchased.

still this is a mission success the antenna works perfectly in both bands and I’ve been using it for over a year with both bands and no issues.

Radio

ALLSTAR NODE

31 July 2025 Cale Leave a comment

#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!

Experimental, Radio

ALLSTAR VOTER

30 June 2025 Cale Leave a comment

#125 Creating a DIY VOTER

VOTER (Voice Observing Time Extension for Radio)

For a while now I have been involved with some troubleshooting at my radio clubs repeater site closest to me.
we have had a few issues where our equipment gets damaged from lightning water and rats.

We’ve tried to mitigate these problems however the reality is that it more of a manage the symptoms situation rather than solve the problem situation.

With this in mind we have had some damaged RTCM devices, the RTCM (radio thin client module)
is connected to the internet and to the repeater. It has an IP address and forwards the voice data to other sites or nodes that have the Allstar system setup. It’s basically like a small VOIP system that can adjust squelch and do simulcasting but the repeater site can choose what settings to enable or disable.

In our case its just connecting the Voice data to the internet so that club members can chat with other repeater/node users over a greater distance through the internet.

E.G: talking to someone in Durban is not possible using VHF at the altitude where I am situated, due to the terrain, large mountains and a hefty over 100Km+ distance away VHF will have a really hard time. Also with all the solar whether these days… I would expect diminishing results.

But… with an RTCM connected to a repeater or a Node, I can now communicate over that distance using Analog VHF radio to the RTCM over the internet and then through the repeater or node on the other side in this case in Durban.

Checking and adding components to the PCB

So now the big issue I had was that RTCM devices will be just under 10K south African ZAR from America for 1 with shipping and all the tax applied it’s very expensive and I wish money was no object but the truth is our club is not super financially inclined due to many reasons a lot of them out of our control.

This prompted me to investigate on an alternative and I found a few but I chose the original 2011 VOTER PCB which allows us to do the same thing basically just on the prototype board.

Of course this rises some concerns like:

THT components used
Parts are all PDIP and most have to be substituted
No case provided
A larger size

Back of the PCB while I was populating it

But… in my case weighing up the pros and cons there’s no major issue using this VOTER version.

So I got a few professionally made, read the datasheets for all the IC’s and purchased the available parts.
I also substituted the parts no longer available and integrated them with some small modifications.
(I will create my own PCB based on this in the future for better availability and usability)

Overall It took me around 3 month just to read all the datasheet and to get familiar with they systems bootloader and firmware of the VOTER PCB not to mention learn about the Allstar system as I had not really been educated on it. Though it was worth it and the research paid off in the end.

I was able to learn fast and I can say that I was happy with this project and the VOTER boards turned out great!!

Electronics, Experimental

MOTOROLA CM140

18 July 2023 Cale 12 Comments

#102 Reprogramming an old CM140 radio

If you do not have the code plug password or a saved code plug with the radios serial number then this post is for you.

I recently came into possession of 2 Motorola CM140 25W radios. These radios belonged to my grandfathers old security company which is now dissolved, however amongst a lot of the kit I was able to save a few gems.

Upon inspection these radios were in immaculate condition despite there age. I was able to power up both radios only to find that they were programmed to one channel and when I used Commercial Series CPS (customer programming software) I could not read or write to the radio since the code plug was password protected.

Luckily I found a sample code plug for the model of CM140 radio I had. This allowed me to clone and change the password of the radio using the sample code plug now I can read/write to the radio

I have created a step by step document on my GitHub page here.

Radical Tech Tutorials

Tag Archives: HAM RADIO

DUAL BAND ANTENNA FIX

ALLSTAR NODE

ALLSTAR VOTER

MOTOROLA CM140

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