Presentation on theme: "Converting The Harris Platinum TV Amplifier For Use on Six Meters"— Presentation transcript:
1Converting The Harris Platinum TV Amplifier For Use on Six Meters And A Discussion of Trends in Solid State Ham Power AmplifiersD. Hallidy K2DH 3/2012
2BackgroundSolid State PA’s for amateur use are nothing new- they’ve been around for decades! Think of the units made by:MirageKLMTokyo Hi-PowerTeleTecTE SystemsThe thing about all of these is that they typically only produce modest power ( W is the typical maximum), are fairly low gain (10-12dB typical using bipolar transistors), and they aren’t cheap!They were designed to provide more RF output power primarily for mobile VHF/UHF stations, running on 12vdc. So their power capabilities are limited.
3BackgroundTechnology has advanced! Today, companies have developed LDMOS (Lateral Diffusion Metal Oxide Semiconductor) devices (LDMOS FETs).High gain, can produce lots of power in small packages (20+dB Gain, Hundreds of Watts to >1kW typical power).Typically operate in the 50vdc range, making them impractical for mobile use, but just fine for home station RF power generation.Relatively cheap!Some companies (for example Ameritron) have designed products for the ham using LDMOS devices. The ALS-600 and ALS1300 are examples of 600 and 1300W solid state HF amps they offer.Some hams have designed high power VHF/UHF amps using them, also. We’ll see examples and references to some of them in this presentation.Some high power commercial LDMOS amps have become available as surplus to the hams, too. This presentation is centered around one of these.
4BackgroundWith the changeover to Digital TV, all broadcasters had to remove their VHF analog transmitters from service, to change over to digital transmitters.Many of these analog transmitters were built by Harris and were sold as the “Platinum” series of TV transmitters.Transmitters ranged in output power from 20kW to 100kW, depending on how many 1kW modules were installed.Very sophisticated units, designed for “Hot-Swapping” failed PA modules, with many levels of fault detection and protection built into them.After these transmitters were pulled from service, some of the modules began appearing on the amateur surplus market, instead of in the dumpster.Two versions exist- low band (Ch 2-7) and high band (Ch8-13). Either can be converted for 6m operation, but the low band version is easiest.Modules were rated for 1kW video service, 24/7 .Will provide at or near legal limit output in amateur service with modest drive (~25W).Here we will discuss the low band version of the Harris amp in amateur service.
5Harris Amp SpecsEach module consists of 16 Philips ON4402H LDMOS transistors connected in 4 pallets of 2 push-pull pairs each and combined.Operates on 50VDC (as do most of the LDMOS power transistors in use today), at about 45A (1500W output).Drive for 1500W out is about 25W, well within range of common 6m equipment.
6Where Can I Get One?I got mine from Steve W1SMS at Microwave Update 2011 this past Fall. He may still have some; he got a quantity of them from WCBS (100kW transmitter) in NYC.Lance W7GJ has been advertising them and still has some.As far as I know, these are the low band versions only.
7Some Images of The Harris Platinum Amplifier Module BIG heatsink!Fault/operateindicatorsDrawer front, used forinserting/removing themodule in its chassis
12Where Can I Find Modification Info? John Sortor KB3XG wrote an article (3 parts) in the Mt. Airy Pack-Rats “Cheese Bits” newsletter in May, June, and August This article is very complete and gives all the steps necessary to convert the low band unit to 6m. He also shows power output achieved, drive and DC power required, and quite a bit of operational data. He also discusses cooling at length- good cooling is a must, as none is provided in the module as it stands alone (cooling was part of the main Platinum chassis). He also discusses the power supply requirements, as well as the need for a high power low-pass filter on the RF output.W7GJ has also written a very complete set of modification instructions. Lance even tells you how to combine two of them for as much as 2.5-3kW out! See the link to his website at the end of this presentation.
13CoolingThe module does NOT include any cooling. Cooling air was provided inside the main chassis into which the modules were installed. Therefore, you must provide plenty of air to the heatsinks on the top of the module.From the various articles, it appears that 4-5 muffin fans above the heatsink will adequately cool the unit, but SUCKING air up from the heatsink, NOT blowing it onto the heatsink.This forces air past the entire heatsink, instead of cooling only the area below the fan (which can also cause a hot spot directly under the fan center).KB3XG built a very nice plenum for his cooling fans that is probably overkill (see image).
14KB3XG’s Cooling System End of unit where “drawer” front would be Image courtesy KB3XG/PackRatsEnd of unitwhere “drawer”front would bePlenum over heatsink, fans on the sideCable to fault/operate indicators
16Power SupplySee the image on the next page. The amplifier requires 50VDC at nearly 50A.This sounds difficult (read: expensive), but it’s not.Blade Server power supplies are available on eBay for $38 (incl. shipping!) which are rated for 57A. These are switchers used in server applications, and are clean and well-regulated. They operate from Single Phase. They are new surplus, no junk, made by HP. The model number is BL20P.
17HP/Compaq BL20P Blade Server Power Supply- 50V/57A
19Hardware Modifications There are not many mods required- they are:DC Power ConnectorThe original DC Power/RF Input/PTT Input connector should be removed and a haevy-duty Cinch-Jones screw-type terminal strip installed in its place for the DC power connections (see images).RF Input ConnectorThis was part of the power connector but a BNC or other small connector can be installed on the end of the chassis very easily (see image).RF Output ConnectorSince the unit was deigned for “Hot-Swapping” and instant plug in, the output connector is not a threaded type. However, it is the same size as a Type N and can be easily replaced with a chassis-mount N female connector which will solder right to the output directional coupler board (see images).PTT Input ConnectionA ground on the violet wire in the original multi-function connector puts the unit in transmit. This wire can be brought out to an RCA jack or another terminal of the power connector.
20Modified RF, DC, and PTT Input Images Courtesy KB3XG/PackRats
21Added Type N Output Connector Images Courtesy KB3XG/PackRats
22Expected PerformanceAgain, it should be emphasized- these amps require no tuning for optimum performance on 6 meters. SOOOOO…Pin=26W; Pout=1475W; Ids=43.7A; Vds=47.3V; Max temp=61.2oC; Gain=17.5dB; Eff=71.4%As you can see, these are pretty good numbers- and these were taken AFTER the low-pass filter was installed!The performance numbers listed above are not mine, they are KB3XG’s. My unit is still a “work in progress”, but should be complete by Spring.I highly recommend referring to both KB3XG’s and W7GJ’s articles for details not presented here.
23What Other Choices Do I have? There’s another TV amp out there (Canadian) called the LARCAN. These were also pulled and made available; with careful searching you might find one- they are similar in power to the Harris amps.You can roll your own! This is not as ridiculous as it seems. There are LDMOS transistors out there that will do >1kW output from 1-600MHz (Freescale MRFE6VP1K25HR6) for about $200 and there are many articles and folks building them- see the links at the end of the presentation for more info.
24Popular VHF+ Solid State Devices for High Power Use Freescale MRFE6VP1K25HR6 (1200W out/1-600MHz)Articles and kits for both 50 and 144MHz 1kw+ amps using this device (DUBUS 4/2010 for F1JRD article). See W6PQL.com for his 144 and 222MHz 1kW amps using this device.Freescale MRFE6VP5600H (500W out/1-600MHz)Article and kit for 432Mhz 1kW amp using 2x this device (DUBUS 1/2012 for F5FLN article).NXP BLF578XR (1200W out/1-500MHz)No article I’ve found yet, but I’m sure there is one, as the price is about the same as the Freescale part.