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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Dr.2N3055 I use dual LDMOS transistors for my home brew transceiver, they are easy to use/bias etc. and so far I havent killed any (but I haven't tried TC duty ! ) you could start with something like at GBP10 each for 85w output you could buy a couple to allow for experimenting. Although stripline/ground plane construction is normally used for LDMOS you can use any construction method that you are comfortable with. A major advantage of LDMOS transistors is their low reverse feeback capacitance (Cdg) and they use gold instead of aluminium metalisation so the silicon can run at 175C, 200C or more without diffusing the metal into the silicon. You can have your rf output and boil water for your coffe simultaeously !
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You can make an instant 2.4GHz VTTC by sticking a breakout point on the antenna of a microwave oven magnetron, and enclosing it in a Faraday cage so it can't radiate. A solid-state version would be a lot more challenging.
Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
Many thanks for the input!
Those LDMOS transistors certainly look interesting. I might try them some day, although I don't know if they are of much advantage when we're still talking about frequencies of several MHz like this coil. I still have a lot to learn about all kinds of transistors, especially in HF duty. Two days ago I graduated from upper secondary school (Finnish lukio) and I'm going to begin studying physics at the university next autumn... Who knows, I might even specialize in electronics although there is a plenty of interesting options (like particle or nuclear physics).
For now, I decided I'm going to lower the duty cycle of the interrupter to cut down on power (as I told, the coil is already drawing more than the power supply rating). I'll be happy to have this coil running on my desk! Then I'll move on to a larger coil, about 1MHz (we're still talking about desktop size), and drive it in PLL and see if a two MOSFET push-pull is any good for low power coils.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I've ordered myself one of those transistors for 'playing' at 10's MHz I like to use uhf transistors because the input impedance is so easy to handle and having the heatsink = source = ground makes life even easier. Some precautions need to be taken to eliminate instability/oscillation but a few ferrite beads is usually enough. My first 'play' will almost certainly be a zvs inverter.
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6.144 MHz tabletop SSTC
