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High power amplifier for 1296
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A Very High Power Amplifier for 1296

Nestled in the amplifier stack in the station, this amplifier uses the new MRF13750 50v LDMOS device, and easily produces 600 watts on 1296 MHz, requiring a maximum of only 10w drive. This makes it an ideal match for most of the 10w radios in use today. Even a low power (2w) transverter will still produce 200w output (the amp has 20db gain).

It was constructed with ample cooling for the high duty cycles of the digital modes (including JT65), EME, and other DX weak-signal work...and uses the standard cabinet size (6h x 12w x 12d) so it matches well with the other high power amplifiers in the station.

Preliminary information (a work in progress) on the RF deck used in the amplifier is located here.

The color scheme is a medium gray cover with anodized front and rear panels in natural aluminum finish (very durable), very close in color scheme to the light gray paneled units shown above and below.

It has all the usual features and safety mechanisms...an internal sequencer built into the control board to coordinate fan control, high SWR lockout, high temperature lockout, a sequenced 12v feed for an external LNA (coordinated with driver hold-off via ALC connection to the driving radio).
 

Here's a birds-eye view of the interior.

At this power level, a Dow-Key high power transfer switch is used for the antenna changeover...very low loss, and one of the few products on the market able to withstand these power levels at this frequency.

The surplus Narda dual directional coupler at the upper right is used to sample forward and reflected power for the bar graph power meters on the front panel, and for the high SWR lockout trigger on the control board. The coupler is mounted directly to the rear panel to eliminate an extra jumper and connector...my thinking here was to eliminate the extra losses of additional interconnects, which mount rapidly at 1296.

The rf deck (on copper heat spreader) is mounted in the center of the heat sink with many of the other components in the system mounted around it.

Three 80mm 40cfm fans are mounted on the rear panel, and positioned to pull air in from the rear vent and push it through the heat sink fins, to be expelled out the front side vents in the top cover (top cover not shown in this photo).

Many ferrite RF chokes are employed to prevent RF from interfering with the operation of the supporting assemblies, and the inside of the top cover is lined with 'Eccosorb', a microwave absorbent material used to dampen resonances produced inside cavities like the one created when the cover is in place. This material also makes internal shielding of the rf deck unnecessary.
Looking at the rear panel shows how the coupler is mounted...it already had 4 mounting holes drilled/tapped into the coupler body near the connector, so all it really needed was a small square cut-out and the 4x hole pattern.

Anderson power poles are used for the DC in and the AC line switch, which is used to turn an external power supply on and off.

All of the sub-assemblies used to produce this amplifier, as well as completed amplifiers like this one can be ordered from the parts page.
 

I thought this photo might be a good one to demonstrate the different color schemes the amplifiers can carry. For those wanting to match darker equipment, the black anodized finish at top left is a good choice.

Just below that one is an identical amplifier in natural aluminum anodized finish with black lettering. This is very close in color scheme to the one at the bottom, which is light gray powder-coat finish, as is the one on the top right.