Building a VHF Packer 6m Amp

I was given this kit by Wal, VK4CBW, as he had purchased it some years ago and knew he would not get around to building it.

The kit was produced and sold by http://www.hfprojects.com in America and came well packaged in a series of sealed plastic packets. Everything including the enclosure and heavy duty heat sink were included.

This little amp requires 1W drive for 30W output and features a Mitsubishi RF mosfet module mounted on the heatsink. There is also a filtered Anderson Power Pole DC input that takes 12V at around 6.2A. And measuring only 5.25 x 3 x 3 inches and weighing less than 1 lb, I figured it would be perfect for SOTA or VKFF operations.

I started my working on the well-made PCB.

Populating the PCB

Then I began making the power cable assembly, the RF cable assembly and the switch cable wiring.

The cables were installed inside the top enclosure case.

I had to fabricate a make-shift mounting plate for the Anderson Power Poles as this was missing from the kit. It has been ordered but hasn’t arrived yet. Eager to avoid delays so I could catch the 6m band opening, I made a replacement out of PCB material.

This isn’t perfect but it would do until the genuine item arrives in the post.

After a little fiddling it went in well and did the job.

The mounting plate in place.

Next, the circuit board and amp module were installed and the initial check carried out.

Ready for alignment and the first smoke test.

The bias current had to be set to 0.7A if the amp is to be used for SSB work, or 0.5A for FM. I chose the former.

The bias current set correctly.

I skipped the next step, which was to align the low pass filter as I don’t have the correct instrumentation. But as I had constructed coils L1 and L2 according to the instructions, this wouldn’t be too critical.

The power output test was more important. I connected the amp up to my Yaesu FT-817 (with power wound back to 1W) and attached my homebrew dummy load and an SWP/Power meter. RF output was shown to be a mere 16W. So I flicked the bypass switch and measured the output as 1W with an SWR of 1.0:1. All good there.

Tweaking the coils of L1 and L2 soon produced the required 30W, so it was time to disconnect the dummy load and attach my 6m monoband dipole antenna.

My homebrew 6m dipole strung up and ready for action.

Keying down produced the power output reading I was after.

RF out was now 30W with the SWR indicated as around 1.7:1. Not bad at all.

Next, I attached my LDG auto tuner to the chain and was ready for an on-air test.

All set up and ready for action.

The result was most pleasing. I worked a bunch of VK7 stations (SSB and CW) and well as VK2s and 3s. I am in business and ready to take advantage of the summer openings.

Oh, and all reports received were most favourable. Nice clear signals, good reports and clear audio were what most operators reported back: they were all impressed that I was only using 30W – most stations were in the 200-400W range.

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Another Power Distribution Board

I decided it would be nice to have a power distribution board made of wood and sporting Anderson Power Pole connectors on the bench. The PCB and power poles were sourced from SotaBeams in the UK. This is what I came up with.

The connectors have been loaded onto a PCB, a nice piece of dark wood has a dado routered and the back panel is cut to size.

I drilled and cut the back panel to fit the PCB.

Cutting the back panel.

Next, the PCB was pushed into place.

The gaps between the connectors was filled with small off cuts of wood.

Next, I cut a second piece of timber to use as a back panel to the backing board. This will protect the PCB as current will be flowing through the solder joints.

I used a router as a crude milling machine to make a recess on a backing board to cover the PCB from the rear.

Once that had been done it was just a matter of screwing the two backing boards together and dropping the completed assembly into the base. This was also screwed into position. A coat of protective varnish was then applied.

All done.

My new power distribution board ready to be pressed into service.

Modifications to my power distribution board

My latest activation (Springbrook National Park) had one positive side affect: I modified my SOTABeams PowerPole PP-4 Way power distribution board enclosure. My original one didn’t provide sufficient protection for the four power pole plugs when in my back pack. Do I sourced a better plastic container, one that came with a removable shelf that fitted halfway down in the enclosure and a lid to enclose the plugs.

I installed the power pole plugs into position on the removable shelf.

When in use, the lid of the enclosure is in the open position.

The shelf fits nice and snugly in the enclosure.

When ready for transportation or storage, the lid clips on in position and the plugs are well protected. There is room for storage underneath the shelf: I might carry spare AA cells there.

A nice functional solution.