I’m only human, so I’m prone to occasionally screwing up just like anyone else. Over the years, I’ve managed to nuke the FET’s in my Ameritron ALS-600 on 3 occasions – and twice it was clearly may fault.
For quite some time, I’ve wanted to make use of a program called “DDUTIL” to automate my Ham radio station, simplifying its operation and greatly reducing the odds of me screwing up – yet again. This program communicates with the Flex 5000’s Power SDR program and allows other devices to automatically sync up and work with with the Power SDR software. DDUTIL is an exceptionally impressive, full featured and best of all – free program! Check it out – HERE.
While I am not sure – it may work with other radios too.
A few weeks ago I completed the process of linking my Steppir control box to my computer for synchronization and control via DDUTIL (after first modifying the box to accommodate a direct USB connection – more on that HERE). Now, as I change frequencies or bands via Power SDR, the antenna automatically follows and adjusts itself – wherever I go. I no longer have to worry about transmitting into an improperly adjusted antenna. That alone reduces the chance of nuking another set of FET’s – considerably.
The next step was to automate my ALS-600 for automatic band selection – again tracking whatever band I was using in Power SDR. DDUTIL has a function that allows you to connect an inexpensive USB controlled relay board – and turn on a desired relay when you select a band in Power SDR. At first, I thought it was going to be a fairly tough project, but it all came together pretty seamlessly.
To begin, I had to figure out the ALS-600’s Low Pass Filter control scheme. It turned out to be pretty straight forward. Below is a partial block diagram.
The ALS 600 has 6 Low Pass Filter circuits to cover all HF ham bands.
The filters are selected by the band selection rotary switch. It sends +12 volts to one of 6 connector pins on the LPF board – each pin is connected to a pair of relays that – when energized – connects the selected low pass filter into the circuit. All of the other filters have their inputs and output grounded – until they are selected.
It took just a few moments with a DMM to map out which band switch connector pin corresponded to which ham band.
The photo above shows the disconnected connector from the band switch in the foreground and the connector from the relay board connected in its place. Only the 6 pins on the left are used. The black wire selects the 20 / 30 meter Low pass filter bank, white is 40, yellow 160, brown 80, grey 10/12, and purple is 15/17.
I installed a ferrite toroid onto the wires, but in retrospect it really wasn’t necessary.
These wires from the new connector go to the USB controlled 8 channel relay board. When activated by the DDUTIL program, the appropriate relay closes and sends +12 volts to one of the connector pins on the LPF board – thus activating the appropriate LPF circuit.
The photo above shows the relay board – in place. There’s precious little real estate available inside so a certain amount of “rigging” must be tolerated. I attached a plastic sheet to the back side of the board to insulate it.
The boards USB jack – the kind commonly found on a printer – had to be removed. The mating connector on the cable was likewise removed and the wires directly attached to the board. It was the only way to get the top cover back on.
The relay board needs a 12 volt power source applied to the 2 pin screw terminal on the bottom of the board. I connected to positive 12 volts by soldering a red wire into the via next to J104 pin 2 on the amp’s ALC / METER board. I scraped away a bit of solder resist on the nearby ground plane and soldered a black wire.
The photo below shows the 2 – carefully dressed – red wires that were added in order to distribute +12 volts to all of the relay “commons”. When a relay is energized, +12 flows from its common to the “Normally Open” terminal. From there it goes to the LPF board and energizes the selected LPF relays.
Below is a partial block diagram of the completed modification. The 160 meter LPF is selected.
Below is a screen shot of one of the DDUTIL set up pages that deals with the relay board.
The screen shot above is a little complicated to explain. Basically – its a table that defines which USB relay is energized for a given band. It’s a bit tricky to set up, and you need to be comfortable converting binary to decimal in order to make the proper “Data” selection. Making matters unduly complicated – Relay #5 seems a bit flaky, so I had to play some games with the programming and wiring configuration in order to re-task another relay. Full discussion of this table is beyond the scope of this post. If anyone is interested in the details – contact me directly.
I’m please to report that the system is working correctly, but needless to say – I’m still playing with it quite a bit, and I’m mulling over a few more options.
The board has 8 relays – but I only need 6 for the LPF’s – 5 really since I will probably never have an antenna for 160. I could effectively disable 160 altogether and free up its relay.
You can’t (legally) use an amp on 60 meters – and (if I remember correctly) you are limited to 200 watts on 30 – a band I never use anyway. Also – while the radio can do 6 meters – the amp cannot. At some point down the road I’ll take action to address those issues.
It should be possible to add a 2nd – even a 3rd antenna port to the amp. Naturally, that will require additional RF port selection relay(s) that are controlled by the unused relays on the USB board. Once installed, I’ll set DDUTIL to automatically select the 2nd antenna port – connected to an 80 meter antenna – whenever I select the 80 meter band in Power SDR .
These USB relay boards are cheap and have a lot of potential applications. The one I bought was recommended by the DDUTIL wiki page. I think it cost about $43.00 – delivered – from Bulgaria. I didn’t notice until later that there’s an even cheaper Chinese made board available on eBay for about $23.00 delivered.
This project AND the amp have been abandoned!
This amp uses 4 of the expensive, fragile and ancient MRF-150 FETs. These devices can supposedly withstand a “whopping” 10:1 SWR. In spite of my best efforts, in the 7 years of owning this unit I managed to nuke FOUR sets of FETs (collectively costing IN EXCESS OF $500.00) . I suspect it had a low pass filter problem that I was never able to identify. Regardless, the design was cheap and the schematic was absolute garbage – all but impossible to follow. I wouldn’t own another one if you gave it to me.
I have since moved on and am making good use of my home brew 1KW solid state amp based on the BLF-188XR. If you can believe the data sheet, this beast can withstand a 65:1 SWR. Clearly, it is vastly superior in terms of ruggedness, power output – and nearly the same price as a set of four matched MRF-150s.
Why MFJ / Ameritron insists on the continued use of the MRF-150 is a mystery for the ages.
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