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Vertical VHF D-MOSFET used at HF

I have a number of salvaged VHF amplifiers that use the BLF278 dual MOSFET. I was considering re-using some of these transistors in an HF linear amp, say 2-50MHz. The data sheet curves don't go below 50MHz, and the S parameters show that it looks pretty squirrelly below 30MHz - see page 20 of this data sheet (I must say, I don't have a formal understanding of S parameters yet; that's why I'm writing):

In order to use this part in the HF range, is it possible to stabilize this part using some RLC network in the gate?

What kind of network is required, and how would you calculate it?

Clifford Heath.

Reply to
Clifford Heath
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My guess is that there is a misprint in the last two S parameters at 10 MHz. If you move the three last values right by one column, the results seem much more believable. It would not be the first datasheet with such errors.

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-TV
Reply to
Tauno Voipio

That looks likely, yes. But I had my eye on the rising s21 phase shifts.

Yes, I'm sure it's possible. I was looking for some insight into *how* to get a stable amp using those s-params. Any advice to offer?

The pictures that Lasse linked show VHFTV modules (single and dual) like the ones I have.

They're linear-ish (class AB) and work pretty well at 144MHz with no retuning, despite being designed for 225MHz. As JL suggested.

Clifford Heath

Reply to
Clifford Heath

Here's a pic of a nice 300W amplifier made with that transistor.

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 Thanks, 
    - Win
Reply to
Winfield Hill

From Broadcast Concepts, I think. They talk about repairing BLF278 FM300-108 pallet amplifiers from Richardson Electronics, so maybe that's the source. TV band stuff.

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 Thanks, 
    - Win
Reply to
Winfield Hill

That looks like a wideband (untuned) part. The higher-frequency dmos RF parts are sometimes wirebond tuned for a specific band.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

looks like theses have version from .5-110MHz

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Reply to
Lasse Langwadt Christensen

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