This N-Channel enhancement mode silicon gate power field effect transistor is an advanced power MOSFET designed, tested, and guaranteed to withstand a specified level of energy in the breakdown avalanche mode of operation. MOSFETs are voltage-controlled devices and exhibit a very high input impedance at dc, whereas bipolar transistors are current-controlled devices and have a relatively low input impedance. The built-in self-regulating actions prevent MOSFETs from being affected by thermal runaway, but still needs some thermal protection R6. Rather than using a toroid which is excellent to match Q1 impedance to 50 Ohms, I have applied the "old school" radio valve coupling; impedance matching circuitry between the output and the antenna using a L-filter FET devices are more closely related to vacuum tubes than are bipolar transistors and because I do like to do things my way HI.
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The HF project was eventually scrapped because of widely varying gain from m to 10m. PCB now available from Far Circuits see below It looked sufficiently interesting, for me to mature the basic circuit design into a singleband 50MHz amplifier.
To make life easy on yourself, use devices from a single batch, as these are most likely to be closely matched. These are no longer being produced, but there should be an ample supply in the distribution channels. The individual IRFs are mounted on the heatsink using Aluminium Oxide heat-transfer isolation bricks and silicone grease, for sufficiently low coupling between the MOSFETs and the heatsink to insure stability. I bought them at Arrow Electronics Nordic at.
The input transformer uses 4C65 cores, and the output transformer uses thin air! See also fig. The end result is then passed through a low loss Elliptical LP filter with a 70dB notch at 2nd harmonic and 80dB at 3rd. Bias is mA pr module; IMD3 has not been measured, but reports on the band have been uniformly good.
More than QSOs have been made so far with this amp. This amplifier now has a power attenuator built-in, to reduce the W from my FT to the 20W required for full output. As do my other amplifiers - all of them! An added benefit is the reduction of splatter produced by the overshoot from the tranceivers output regulator, the more you throttle back the worse it gets - some modern tranceivers produce spikes of more than W on VHF - and the FT is far from the worst of the bunch!
You can, of cause, combine an arbitrary number of the W modules to obtain your desired output level, my reason for deciding on W was the availability of a suitable powersupply. Etched on double sided material. The finished module since the PCB design, I have added the bias circuit in the upper right corner - dead bug fashion Click to see hi-res version. The small circuit added to the heat-sink, next to the bias circuit, is a fan-speed controller see elsewhere on my homepage The completed amplifier as usual, click to get hi-res version The large finned object is a surplus commercial W Switch Mode PS.
On top of that the Elliptical LP filter. The small PCB over the PS, contains and 24V regulators and changeover relays not seen, but cheap open frame 20A Washing machine type, but still better than dB return loss at this frequency! The coils of coax cable are the splitters and combiners Last, but not least, the whole thing - ready to plug in - weighs just under Just recently i was hunting a very rare Norwegian square, and had to turn off the amplifier during recieve periods in order to be able to decode him at all!
It quickly turned out to be RF-Hash coming from the SMPS and the Fan, but various attempts to get rid of it it proved fruitless, and, I realized that, instead of curing the decease, I had to do something about the symptoms. The noise entered my signal path at several points internally to the amplifier demonstrated by taking the two coax-cables connected by a female-female adapter, routing this through the amp, with no detectable noise when the amp was turned on. The main culprits were determined to be the open frame RF-relays and coax joints done on the cheap at various points.
I thus decided to completely redo internal RF-cabling, using high quality coax relays, cable RG and crimped N-connectors throughout. The modified internal layout! Addendum Jan. The reason of this message is to share information and experiences, if some builder asks for help.
Looks like i have found a remedy for the parasitic oscillation problems, which may occur with vishay brand irfs. I did install 4r7 SMD resistors in series to gate lead, right to fet:s gates, and that was right for the money! Now the amp looks like it is full stable at any bias voltage, what i have tested few hours.
I have tested with 28 to 40 volts, no oscillations whatsoever, nor when stopping to transmit and the bias left running. One thing i noticed too, the input WSWR also improved from good to exellent. It was abt. Maximum gain with these was well over 12 db before the resistors, but unusable due the oscillations.
Also with 5w input, a 28 volt supply produced better efficiency. Next i will test with 10w drive and 40 volts, when i get bigger power supply and rig capable of 10 watts.
50MHz 500W IRF510 based Amplifier
I have had a suitable box laying around for quite some time that was perfect for the amplifier project. I decided to go for Manhattan style construction using mainly the parts I already had in my junk-box and not order the PCBs and toroid set which are available from different sources on Ebay. In other words: a low-cost project. The first I did was to make room for the IRF mosfets and two heat sinks.
IRF510PBF - Transistor IRF510 Mosfet N 100 V - 4 A - TO-220
So truly a lot of bang for your buck. You also will need a suitable heat sink -- just idling at ma of bias and using a The "easy access part" becomes critical if you buy those unmarked Chinese specials sold for a quarter a piece! Many questions have arisen regarding proper biasing -- if you are up to your neck in anal retentive things then shoot for around ma with no signal applied. My process: I set the bias by listening to the signal connected to a dummy load on an outboard receiver. There is a sweet spot where the signal sounds very clear and there is no output on a scope or RF power meter with no modulation -- quite often that is awful close to Ma.
IRF510 MOSFET. Datasheet pdf. Equivalent
The HF project was eventually scrapped because of widely varying gain from m to 10m. PCB now available from Far Circuits see below It looked sufficiently interesting, for me to mature the basic circuit design into a singleband 50MHz amplifier. To make life easy on yourself, use devices from a single batch, as these are most likely to be closely matched. These are no longer being produced, but there should be an ample supply in the distribution channels. The individual IRFs are mounted on the heatsink using Aluminium Oxide heat-transfer isolation bricks and silicone grease, for sufficiently low coupling between the MOSFETs and the heatsink to insure stability.