I’ve recently built another AllStarLink node to compliment my personal 70cm band SHARI node as I thought since I have a full duplex dual band handheld it would be great to have another node that I could connect to FreeStar or HUBNet at the same time as monitoring the Matrix node.
Rather than build another personal node I decided this time I would build a public node, obtain a callsign from the RSGB and make it available to the HAM’s locally on the 2m band.
This would make it possible for me to monitor both nodes at the same time using my Wouxun KG-UV9K full duplex dual band handheld whilst providing the local HAM community with access to the AllStarLink network.
Initially I thought I may be able to use my old Retevis RT85 handheld and AIOC board for the 2m node but, after a little testing it soon became apparent that it overheats during long overs (which are common on AllStarLink) and so, I needed to find another solution.
Chatting about this in the main Matrix HAM Radio room Steve, M0XVT sent me a message saying he had an old Key KM-4000 converted PMR radio that had been reprogrammed for the 2m band that he was looking to sell and that it might be ideal for the new node. Wasting no time, we came to an agreement and I was soon the proud owner of a converted PMR transceiver.
The KM4000 transceiver has a standard output of 15w, 10w more than I needed for the gateway and so I had to reduce the output. A quick search on the internet and I found the Thames Valley Repeater Group website that had all the information required to turn down the output.
I also had to reprogramme channel 1 to the frequency and CTCSS tone allocated to me by the RSGB so that in the event of a power outage when the radio came back on it automatically jumps to channel 1 which would be correctly setup for operation.
Unfortunately the software for programming the radio is only available for windows and so I had to build a virtual machine running windows 10 to be able to reprogramme the radio.
Once this was done I rewired the AIOC USB audio device to work with the KM4000 radio and built the AllStarLink node on a spare RaspberryPi 4.
For an antenna I made a simple end fed vertical dipole from some RG58 coax and mounted it 8m up on one of my Spiderpoles in the garden. Running a coax feed out to the antenna I did some tests into the Parrot to get the audio levels setup and checked that the DTMF codes were interpreted correctly and that the node switched connections without error.
Once this was done I had a few test conversations with stations on the Matrix node and FreeStar to ensure all was fine and then set the gateway status to “Operational” on the RSGB website.
This worked fine for a while with myself and some local stations using the node regularly but, then the hot weather arrived and things started to overheat. The transceiver was getting incredibly hot in the 30c+ summer temperatures and the power supply was also running extremely hot and so I decided to add some cooling.
Cooling the PSU was simple, it has a perforated top panel to which I strapped a cooling fan. This worked great and brought the temperature of the PSU down considerably.
The radio wasn’t so easy to cool. It has a solid case cover top and bottom and so cooling wasn’t going to be a simple affair.
I decided to remove the covers and drill some holes into them to allow airflow through the unit and strapped a fan to the top cover to pull the hot air out. This worked well however, on both transmit and receive I now had a warbling sound on the audio that was caused by the motor of the fan when powered up.
I found that lifting the fan up away from the case of the radio the warbling audio disappeared and things were back to normal and so, I decided to design a cooling tube to fit to the top of the radio to allow full airflow from the fan but, with the fan raised up away from the radio to resolve the audio problem.
Jumping into my CAD software I quickly designed a cooling tower to fit on the top of the radio that would allow the fan to sit far enough away from the radio so as to not affect the audio whilst at the same time pulling the hot air out of the radio and drawing cooler air in through the bottom of the case.
I sent the design through to my Bambu Lab A1 Combo 3D printer and set the print job running.
The cooler worked great with the radio staying cool to the touch and no longer overheating and reducing O/P power.
It’s amazing how much dust and dirt is in the air from all the farming activities going on at the end of our garden and how much of it is sucked in by the cooling fan. Regular cleaning is a must!
The MB7IBW Internet Gateway has been on air since mid June 2026 and has worked well. It spends most of its time connected to either FreeStar or HUBNet with connections to the Matrix Node when we have our nets.
Details on Frequency, CTCSS etc can be found under the MB7IBW menu above.
Sadly the initial interest from local HAMs has now wained and I am mostly the only user of the gateway. I was hoping more people would use it and bring some life to the 2m band, I guess time will tell.
It’s been a fun project and was interesting to go through the callsign allocation process with the RSGB representative. It was much easier than I thought it would be.
I now have all the parts to build another Internet Gateway for the 4m band. Hopefully that may attract some more interest. It’s certainly worth a try!
More soon …
