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FET drain bypass caps




 
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Author Topic: FET drain bypass caps  (Read 506 times)
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GW0FZY
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« on: February 25, 2018, 05:32:44 AM »

Chaps,
I had quite a bit of difficulty finding the UTC porcelaine caps recommended for the drain bypass in the RF deck. Could not find anyone in the UK who had them and they were going to cost a bit if I had to have them sent over from America.
I used these large ceramic SMD’s in parallel soldered togther with some copper foil and they seem to work up to the full output power. If anyones interested here’s the info from Farnell
http://uk.farnell.com/vishay/vj2525d271kxoat/cap-rf-hi-q-270pf-2-5kv-2525/dp/2420175RL

Justin
GW0FZY
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steve_qix
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« Reply #1 on: February 26, 2018, 10:27:49 PM »

Do you mean the shunt caps (the ones that run from the drain bus to ground) ?     These are usually between 1000pF and 1500pF for 4 to 6 FETs per module, on 75 meters.

The bypass caps are the .15uF (or thereabouts) capacitors.  These too must be able to handle the current.  I use 3 .047uF orange drop caps in parallel on each module for RF bypassing.
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GW0FZY
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« Reply #2 on: February 27, 2018, 01:26:31 AM »

Yes the ceramic shunt caps Steve, that's what I meant!!
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