This post was originally about IRF620 mosfets but I deleted my original post and decided to just make a post about mosfets in general.
I think a very good technique being used often lately in pirate radio for the HF frequencies is the use of mosfets in the RF amps and the modulators.
If you didn't already know, power mosfets work really well into the HF frequencies and there have been some really good schematics and projects based on them. One of the first projects created for pirate use was the Grenade built by Radio Animal (WKND) and a few were made in the 90s.
Anywho you can google around yourself and learn the history of it all. Hams have been using hf power mosfets for some time now but most of the projects they designed seemed to be based on really expensive parts compared to the ones used in the pirate radio circuits.
Some of the most common in use are the IRF510,511,520,530. I have found that some of the other IRF series work just as well. It seems some people have forgot about using scrap parts though. I got a large 400 watt car stereo amplifier out of the junk and it had 8 of FQP50N06 mosfets and all of them worked but one. Rated at 6 amps, 60 volts they work perfect for my new MW 10 watt transmitter and I didn't pay anything.
Another good source of mosfets, sometimes really high power/wattage output ones are right inside old computer power supplies.
Class D and E transmitters seem really easy to build. With only a few parts it isn't hard to make a transmitter from 10-50 watts or even more.
Using bias on a mosfet you can easily make a linear amplifier so that you can modulate at a lower stage of the design so that low power modulators can be used. If you already have a good audio amp you can simply high level modulate the mosfet but it's somewhat inefficiant, but simple enough to build for beginners. Also if you have the know how it seems best to use PWM (pulse width modulation). It's the most efficiant wat to use a mosfet because all of its power is either in on/off states, so most all of it's power supply voltage becomes it's drain voltage.
So anyone interested in mosfets used in HF are more then welcome to drop in.
Here are a few links to some neat transmitter schematics that use mosfets, from most simple to complex...
Post by Peter Scott on Jun 11, 2008 21:44:30 GMT -6
Hi all, I want PCBs for Commando and Corsair Transmitter. I am not that good in electronics- and for security purpose I can not request anybody sorrounding me either. Do you guys have amy idea that who can supply me the PCB for the transmitters? Also, I want a components source too. I'm from Australia. Thanks.
I would imagine that you may have to design or etch your own PCB for these, you can find info on making your own PCB's on the net or often at your local library. You can probably build it without a PCB, it will just look ugly and you will need a good ground. From looking at the schematics, most of the components can be salvaged from old boards, (as Darklife has done) and the cores can be hand-made. The Free Radio Network had a long discussion about these about a year ago. Good Luck.
Hi all, I want PCBs for Commando and Corsair Transmitter. I am not that good in electronics- and for security purpose I can not request anybody sorrounding me either. Do you guys have amy idea that who can supply me the PCB for the transmitters? Also, I want a components source too. I'm from Australia. Thanks.
MOSFETS are fine little devices, if people can drive them correctly.
One of the things people forget is the gate capacitance - can be hundreds or even thousands of picofarads. There's two ways to deal with this, swamp it by driving with such a low impedance it doesn't matter (like using a 1 or 2 turn loop over the driver coil - needs extra driver power) or resonate it with a tunable inductor. This can be in the nanohenry range for the bigger power MOSFETS, or ones with super low Rdson.
Secondly, if you want more than 5 watts dead carrier out of any MOSFET at 12V Vdd, go push-pull. If you wan't to be able to modulate it with an auto battery supply volts, you'll need some sort of transformer, because emitter/source fed follower modulators ain't gonna cut it!
While bipolars are cabable of tens, even a couple hundred watts dead carrier at 6V Vcc for follower modulation, MOSFETS will still be a far less expensive way to go. The MRF series bipolars will clean your pocket and are somewhat static sensitive and physically fragile. The extra money is better put into a DC-DC converter to give a MOSFET 50V Vdd or something from 12V.
Darklife mentioned parting a car amplifier - grab the power supply as well as the MOSFETS.... there's your Vdd supply from 12V
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