The "Easy" 432 MHz KW+ SSPA with Freescale 50V devices
Fancy some real power on 432 MHz?
DUBUS recently published a design for a 432 MHz 500W SSPA using MRFE6VP5600H devices. A first stab at 432 MHz using the new Freescale LDMOS range.
A nice compact design on a small PCB was published that uses the same 50V format as the 1KW PA for 50, 144 and 222 MHz. Since that article was publised earlier this year there followed a number of articles on combining these but these invariably use coax combiners which in my opinion are bulky and messy to make.
So I am pleased to announce that Jim W6PQL has managed to create the "dream" 1KW+ SSPA for 432 MHz using 2 x 5600H devices.
These 2 devices are combined using a small commercial coupler on the input and a printed PCB coupler on the output. The output combiner is printed onto teflon microwave PCB to handle the power and heat at the 1KW level.
I had the pleasure of helping Jim test the 500W board designs at his Fremont QTH and can say they are very nice designs and well built.
This is a real neat design and encompasses the mods and improvements that Jim has developed over the past 12 months or so while developing 144 and 222 MHz designs using the Freescale range of 50V LDMOS devices.
This is personally the breakthrough I have been waiting for - no messy coax combiners - a single board with 2 devices and easy combining - no messing with coax.
I received my board kit last week and over the past days have managed to get the board made up and the heatspreader milled and drilled.
The board is easy to build and probably easier than even the 144 MHz pallets - and they are not particularly difficult to build.
The heatspreader was milled up and drilled and tapped by Chris ZL3LF - whom I thank for his excellent work which made mounting the devices and PCB's up very easy.
The devices are soldered to the heatspreader - I use a large plate of aluminium on the stove top and heat the spreader indirectly. I used some solder paste that melted assoon as the block reached the critical temperature and I then used a damp cloth to spread the solder across the small milled gutter until the area under the devices was well tinned.
I then dropped the devices onto the right areas which I had notched with a craft knife so I knew where to locate them. I spread a very thin layer of solder paste on the base of the device andthen drop it in place - leave for a few seconds and then give a little shuggle side to side so it beds in. After that remove from the heat and let cool slowly to ensure no thermal shock. Once the heat hasstarted to reduce I use a cold tap to chill the pallet down to a manageable temperature.
Once its all mounted up I defluxed the board using alcohol and we are now ready to bolt down to a heatsink and do some tests which I will publish soon on here.
Watch this space :)
You can find more info at Jim's page over at www.w6pql.com
Last Updated (Sunday, 24 June 2012 00:57)
About the 432 MHz Band ….
Although maybe not as popular as 144 MHz, the 70cms band has in similar ways undergone the same technology revolution as its lower band neighbor. The introduction of solid state low noise receiver frontends, MOSFET power amplifiers and computer generated digital modulation, DSP techniques and optimized yagi designs have all evolved at 70cms too. The band is very similar in nature to the 144 MHz, offering a broad array of modes such as FM, via simplex, repeaters, IRLP/Echolink nodes etc. SSB and CW are very popular, as well as newly introduced modes such as WSJT.
Although similar in characteristics to 2M its worthy of note that this band is above the cut off frequency for Sporadic E. Mainstay modes such as Tropospheric Ducting, Meteor Scatter and Aurora are all present on this band and in fact some modes such as Tropospheric Ducting are more prevalent due to the smaller wavelengths. All of the main manufacturers offer transceivers in the same guise as their 144 MHz options either as single, dual or multiband options. Again transverting remains popular for high performance stations, with a number of suppliers offering kit or ready built equipment.
Readers should also refer to the 144 MHz band description for supplemental information.
Last Updated (Monday, 17 May 2010 23:25)