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1kW LDMOS Linear Amplifier – Part 1 (PSU)

Based on designs by W6PQL

First step in building such an amplifier as described here:


is rigging up a power supply capable of delivering 50Volt at more than 35Amp.

There are a number of ways of doing this, telecoms power supply units (48V) can often be found on ebay, but like server power units can be very noisy. Its also possible to put together sets of 12 and 24 V switched mode PSUs with steering diodes etc to build a powerful combined unit. W6PQL describes such an approach on his web site.

I was lucky in that I managed to find a surplus Meanwell 48V 2400W power supply unit going cheap. Therefore my PSU is basically one of these units, encased in a slightly larger box with the addition of some switches and an ammeter to measure the current. Simple.

This is the front view

The connections are at the rear.

Inside its very simple.

With the top cover removed

In this image you can see the Anderson PowerPole connectors for the DC output on the rear and the cabling to them with ferrite beads aimed at reducing the RF on the wiring. Theres also a 75mV shunt on the negative output which is used to drive the ammeter on the front panel.

The pSU can be remotely turned on and off by shorting the remote input (two blue powerpole connectors) together from the attached LDMOS amplifier, or by setting the front panel switch to local.

Backyard HF Antenna project

I have been planning a return to HF operation, so the question of stealthy (small) backyard antennas comes up.  The available space is the typical ‘not much’, roughly 55ft by 30ft

Plan A is an inverted L, fed via an auto ATU at the far end of the garden, with the horizontal section of the “L” coming back towards  the house. So far A CG3000 auto-tuner has been obtained on ebay, and a 12m “Spiderbeam” telescopic fibreglass pole.  Every plan should have a sketch, so here’s mine:


So the ATU will not tune easily a length of wire close to 1/2 a wavelength or multiples pf half a wavelength.  I reckon the wire length will be around 23m.   I have to keep away from 21m  which is a half wavelength at 7.1MHz and multiples at 14.2 and 21.3MHz (!)

I plan to run radials under the lawn and along the bottom part of the wooden fencing.