Category: Ldmos amps

I recently watched the movie Fat Man and Little Boy, a great movie about the Manhattan project and the development of the atomic bomb. Paul Neman is the lead character as an army general assigned the responsibility of delivering the bomb. John Cusack plays the role of a very bright mathematician and scientist from the University of Chicago.

ldmos amps

Toward the end of their efforts many of the scientist, especially Cusack's character, begin to think about the moral issues of what they are about to achieve. The movie centers around the collaborative effort to affect the end result with a lot of very independent minds and ideologies. The film reminded me of how we amateurs work together exchanging ideas and helping each other with all sorts of issues - antennas, radios, projects - etc.

Silicon-based LDMOS FETs are widely used in RF power amplifiers for base-stations where requirements for high output power with a corresponding drain to source high breakdown voltage ratings are required - typically cabable of very high frequencies. Exchanging ideas with many of my ham friends for this project has been the key for its success.

After two failures with LDMOS chips it was pointed out to me that the source to drain voltage ratings of the devices being tested was not high enough to take the 55VDC analog power supply being used. As a rule of thumb the rating should be divided by a factor of "2", and that would mark the upper limit. The original unit we used had a rating of volts so anything over 50 volts was likely to result in a "failure".

Viewing the NXP device was scary when thinking about heat dissipation. In dealing with this issue some designers have channeled out the copper plate used to disperse the heat and soldered the units within the indentation.

ldmos amps

This seemed extreme to me so I just went with the conventional application by bolting it directly to a copper spreader with a good dose of heat transfer silicon. This is working okay as the heat gets moved away from the transistor sufficiently to stay within its design parameters - the junction temperature limit of the NXP transistor is C I would think it would melt at this level! Some hams have used a clamp on top of the unit but I did not see the advantage and worried about possible damage.

LDMOS chips are "Gemini" - literally translated as "multi faced" - and have two transistors incorporated within the same chip. This is the perfect combination for a "push-pull" design and significantly reduces the cost.

The NXP engineering group provided their ideas for a HF schematic as shown below along with a list of materials. The feedback resistor looked a little light to me - FYI they don't show the bias supply and regulations circuit. I could have "rolled" my own board following the schematic provided by NXP.

However my objective at the outset was to use offerings from third parties to lessen the project's obstacles. Most of us have busy lives and don't have the time to put it all together - including me. Using Skype and email we communicated regularly about the design and application I had in mind. His experience with other hams and overall expertise has been a big plus. In simplest terms the transistors have very low input and output impedances so the drive has to be lowered and the output increased to feed the Ohm source and load.

The input and output transformers are usually engineered with sometimes and ratios, in RF terms - 9. Baruch appeared to follow the NXP model using toroids hand wound for the output stage. The board features a high power transmission line transformer wound on stacked ferrite toroids modeled after a design by ON9CVD - resulting in lower IMD and less saturation at higher frequencies.The transistors used are extremely rugged and can withstand an SWR mismatch for or greater at all phase angles.

The bias current is preset to mA and can be readjusted by use of 2 independent potentiometers. The board dimensions are 4" wide by 7. I also provide free technical support by email. Product Description:. Watch my video to see the RF Amplifier in operation. For repairs, Buyer pays shipping costs to ship to seller and return costs to ship back to buyer.

Before returning any RF module for repair, please contact the seller to coordinate the return or to request a cost estimate in advance. Legal Disclaimer:. The Buyer assumes full responsibility for compliance with all applicable regulatory agencies and laws. By purchasing this RF Amplifier you are agreeing to all terms and conditions stated herein. This amplifier used high level of electrical power. Buyer assumes full responsibility for the application and safe use.

The Seller assumes no liability for the the use of this product and is not liable for any damage to equipment or personal property. Further, the Seller assumes no liability for personal injury or fatalities that may occur to the buyer or third parties if resold.

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Buyer agrees to use this product at his or her own risk. To the maximum extent permitted by law, the seller disclaims i any and all liabilities arising out of the application or used of this product, ii any and all liability including without limitation special, consequential, or incidental damages and iii any and all implies warranties including warranties of fitness for a particular application, pass through warranties if the product is resold, and all non-infringement rights.

Operating Voltage 50 - 56 volts DC. Current Draw 40 - 50 amps.

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Input power 1. Idle Current mA. Operating Class AB. Cooling Requirements forced air. Assolutamente tutto perfetto! Legal Wavier: By purchasing this RF Amplifier you are agreeing to all terms and conditions stated herein.That requires an antenna with as much gain as possible, and a powerful amplifier. This whole undertaking was a huge challenge, and as usual I learned a lot Jim clearly had major problems with EMI, judging from the large number of toroids he has scattered around the interior of his enclosure.

He also resorted to RF absorbing material to line the inside of the lid. I believe toroids are Band Aid and not a great solution. I prefer a more systematic approach using shielding and filtering The source of EMI can either be radiated through space, or coupled into signal or power wiring and propagated into susceptible circuitry Conducted. We deal with Radiated Emissions by the use of shielding. We contain Conducted Emissions inside the shielded enclosure by filtering all wiring that penetrated the shielding.

We protect susceptible circuitry from Radiated Emissions through the use of shielding.

HF Power Amplifier 6000w test Part1

We prevent Conducted Emissions from entering the shielded enclosure through the use of filters. The concept is quite simple - seal up the bad stuff inside an RF-tight enclosure and trap any conducted EMI through the use of filters. It's the execution that can be a challenge This is a common type of in-line EMI filter that can allow a signal or power conductor to pass through the wall of a shielded enclosure, while trapping conducted EMI.

Look at the specs That's going to stop conducted EMI dead! How well my homemade enclosure works will depend entirely on how well I did in eliminating even the smallest gaps. I found out the hard way that even a commercial die-cast aluminum enclosure, with the lid screwed down tight did a horrible job at shielding. This is the top view, with the lid off. Initially I had planned to use bulkhead feedthrough RF connectors to deal with RF In and Out, but Type-N connectors take up a lot of room and are marginal at this high power level.

I ended up simply drilling a clearance hole in the ends of the enclosure and passing the coax through. I'll show you how that worked in a few slides Getting back to the coaxial cables I made small rectabgular pieces out of. Using a tapered awl I carefull tapped it into the small hole and enlarged it for a tight fit. That created a tunnel so I had some surface area to solder the coax to.

After aligning that piece, I pushes the end away, soldered the coax, then slid the and back and screwed everything together. In my schematic you can see that all signal and power lines pass through EMI filters when penetrating the shielded enclosure. There are a lot of components on this board.

That's why I recommend buying the assembled and tested board and not the kit.I built this in an afternoon and it most resembles the Elecraft amplifier from the drains back output section. The Elecraft output section design looked pretty elegant and simple.

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So I wanted to try and copy it and see how it performed. That said, none of these amps with the CMFC scheme you see here, and other similar ones, can ever be linear. I test up to W CW key down. Then I usually run it up to 2kW just to see what kind of headroom above W that it has. Your amplifier is really good looking, very professional design. We can all learn from your experience.

I would love to see a schematic if you have one. Good morning. I post what I am comfortable posting. Too much time and effort went into getting the circuit perfect. For my dual 1k80h pallet, the values are different for the same outcome. If I change Vds, the values all change for either amp. Hello, this design seems to be very similar to the KPA I would suggest to add negative feedback and a ground resistor at the gates to avoid common mode oscillations.

Do you supply 65 volts to it? Good eye. Rob, Thank you. Looking more closely, I see that you already have a path to a 10 ohm ground at the biasing network through the transformer secondary.

I would have placed the ground path closer to the gates and not in series with the transformer inductance. Ohhh and I forgot the compensation: For the first transformer you used TC coax, which has around ohms Zo instead of the ideal 6. This along with the PCB traces to the drains represent some leakage inductance or mismatch that you will have to compensate to reach 6m band.

What are your findings?

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I wanted to know about the heat dissipation capabilities when not bolting down the LDMOS or Soldering the bottom to the copper Heat sink. All the years of building audio amps with mica insulators and thermal grease. Never looked back.One of my design goals is to be able to run full power for extended periods of time, primarily for EME work, so first problem is design of a sufficient cooling arrangement: This is what I came up with: The heatsink itself is 35x20x10cm and weighs about 7Kg, with the Cu heat-spreader 10x35x0.

Now it should only be a question of moving a sufficient amount of air through the heatsink, more on that later. This was accomplished using solder paste and a household oven this process smells BAD, so don't do it while the XYL is home it took about 1 hour with the termostat set to degrees centigrade before the solder finally melted and completed the baking phase!

I had to bake the entire assembly, as some of the screws mating the Cu piece to the Al one are located underneath the PCB remember this part of the project was fabricated prior to the adoption of the LDMOS device.

A check with a transistor tester showed that the two separate transistors survived the baking process! Actually soldering components onto the PCB attached this way, is a cast iron bitch - I finally heated the whole assembly to some degrees again to accomplish this, particularly the through-plated ground pads are difficult because of the excellent heat transfer of this assembly method which was the goal anyway.

He prescribes that they be mounted on the edge and as close together as possible, I took a chance and remounted them loosing only one 15pF cap in the process - luckily i had a spare in my RF-components junk box.

This i what it looks like after the remount:. The RF-module is now complete but still untested and I am working on the completion of the F1TE control and safety circuit. In the middle two Radiall 24V coax relays, and on top of the power supply LP-filter and Directional Coupler, these will probably be relocated to fit next to the relays later.

The white twisted wire hanging over the side with a invisble push-button switch at the end is for Fault-simulation during testing. You do, of cause, use a decent LP-filter in you amplifier - don't you? Cook, with very good rejection of 2'nd and 3'rd harmonics and miniscule insertion loss:.

From the front And finally from the front with operational controls and indicators. The first power-up current limited power supply went fine with no signs of oscillations or other untoward phenomenons.

After a few attempts to adjust the gate bias correctly I noticed the silk-screened " first " next to the mode "B" adjustment no mentioning of this in the documentationand from then on adjustment proceeded smoothly. Time had come to move the RF-module to the internal high-current power supply!

These were two of the caps I relocated after being told that they were less than optimally mounted, one blew and the other was badly singed.

Please bear this in mind as you read on.N6QW makes yet another attempt to lure you into the homebrew world! One of the biggest issues maybe ranking near the top are the problems with putting a RF Amp in line between your transceiver and the antenna system. The Arduino is ideal in this case as there can be logic incorporated into the control functionality to add a high degree of protection. The appropriate low pass filter was not selected --so the output side is not connected but the input side is - smoked the final.

Let us now take a tour through this schematic. So any action that causes the main supply to be off will cut off the source of power to these relays. Pretty cool! In essence a command to put the amp in line must be seen as a grounded input passing through the LED16 relay contacts and ending up as a "LOW" signal on analog Pin A0. There is nothing special about using an Analog Pin --it could have been done with one of the Digital Pins --but I did want to experiment with the analog pins as they will play an important part with the sensors.

But let's go back to LED A second here about normal off and emergency off. Normal OFF lets you start the amp immediately as does Bypass. But with Emergency OFF you must wait 40 seconds or however long you want before you can restart the amp. This is purely so you are forced to think about the "why" this happened before you tap the "On" switch.

This was done by satisfying a multiple "OR" condition represented by two parallel lines.

LDMOS Amplifier

I guess this may be the first time I used a logical OR condition with the Arduino. Two "if statements" are needed with one to detect if any of the LPF relays are in line or to detect if none are in line. Try that with just toggle switches! Two LED signals are used so that they can be sequenced with a small selectable difference in time. Just for safety in case something gets smoked with the 2N's I will probably add a couple of 1N diodes in series with the 10K resistors to prevent an voltage being back fed into the Mega Cheap insurance!

But to that, end what I will be sharing with regard to the use of an Arduino Mega has other applications like building a control system for a Beacon transmitter or perhaps switching antenna systems. So there just might be a nugget or two worth your time. I am not an Arduino expert but am simply an experimenter that has been lucky enough to get a few things to work. There had to be a lot of noodling to get that to play. So its here and why not use it.

But employing an Arduino requires thinking about things differently. Would it work? Of course it would work! But there would have to be a lot of manual intervention and were a critical situation occur, a manual intervention on your part would be required. Lets start our thinking differently with our motor starting example and the two switches SW and SW1. So how would this be represented using an Arduino. To answer that question we will use the diagrams below.

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In writing the code for the Arduino several things must occur and these include identifying that there is an integer number identifier that can't be changed. Now lets get back to the event that will trigger SW or SW1. So now the naysayers will shout --we could have done that with manual Push Button switches which is of course is true.

BUT suppose there is a heat sensing device on the copper spreader and there is a temperature rise sufficient to cause concern?

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Separately there is code that when that heat rise reaches a pre-determined level there is internal code that essentially triggers SW and the supply is shut down. So the same basic code that normally shuts down the power supply can also be embedded into other call functions to shut down the supply.In the pic you can see the exciter Flexspectrum analyzer, power supply, dummy load, RF power meter, ammeter and oscilloscope.

Hiding in the back is a inline RF sampler. The way I test and develop these amps is very unique. This method is extremely easy and does sell amplifiers, since hams only care about watts…and how cheaply they can get them.

Those commercial amplifiers are not really linear by any stretch of the imagination. If any amplifier was truly linear, it would not even need a LPF. I test my amps with no LPF, full power into a dummy load. I watch the sine waves and watch the spectrum analyzer, primarily the 3rd harmonic. The 3rd tells the story. Anything above that and the waves take on all sorts of predictable non-linear shapes and the harmonic content rises to unbelievable levels — like 3rd harmonics only dB!

This is NOT linear. Here's my latest dual 1K80H amplifier, mostly in pictures.

ldmos amps

Actually, this is not "my" design. I built this in an afternoon and it most resembles the Elecraft amplifier from the drains back output section.

Last year I decided I would design and build a regulated temperature-compensated independently adjustable dual bias circuit for my 2x LDMOS amp. So I've gone around the block on this one. Tried a bunch of designs, studied a bunch of others and finally designed my own!

The goals of the bias circuit include: Present a well regulated, extremely clean DC bias to the gatesAllow for a very … [Continue reading] about Biasing Schemes Revisited.

It's a pretty simple test whereby you simply run significant power through the TLTs and measure the temperature … [Continue reading] about Transmission Line Transformer Testing. Heck yeah!! Footer Newsletter Signup.

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