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Author Topic: Best MMIC amplifier?  (Read 1477 times)
KB1GMX
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Posts: 1786




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« Reply #15 on: May 20, 2019, 10:28:52 AM »

MMICS are nice when I need gain above 200mhz, below that I
have to live with the excess wide band width and possible effects.
Using a mimic without selectivity before it will nearly always end
up with some RF from some unwanted source causing havoc.


Like many I've used the G4AON and SV1AFN circuits for the last 40+ years. 
They are old and the devices are well known with predictable performance.
It seems every 10 year or so they get rediscovered.

FYI the 2n7000 in a suitable circuit is very much similar to those and only
slightly more modern.

The last compendium of wideband HF amplifiers in my collection is
September 2002 73 mag.  I'm sure there are others since.

Allison
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G0HZU
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Posts: 162




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« Reply #16 on: June 07, 2019, 06:16:15 PM »

For low frequency stuff (up to the 2m band?) you can make a reasonably good wideband alternative to a 50R MMIC amplifier using a BFR91 BJT transistor and a few resistors and caps to define the feedback. It won't have the same bandwidth but it should work well as a basic low power 50R gain block up to maybe 150MHz and it would be 'strong' enough to use as a driver amp for a level 7 diode ring mixer for example.

One downside would be poor reverse isolation but this affects a lot of MMICs as well. It would work best up to about 70MHz with a decent frequency response similar to a 50R MMIC. It would probably only be good to about +7 to +10dBm in terms of the 1dB compression point but it depends on how hard it is biased.
« Last Edit: June 07, 2019, 06:33:14 PM by G0HZU » Logged
G0HZU
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Posts: 162




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« Reply #17 on: June 07, 2019, 06:32:41 PM »

Use a pair of BFR91 BJT transistors as a classic wideband DC coupled amplifier (50R in and out) and you can get flat gain to >200MHz and also 60-70dB reverse isolation across the HF bands. The noise figure won't be great but this might not matter as much as the reverse isolation. It won't be a very strong amplifier either but that doesn't always matter either.
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N3DT
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Posts: 1618




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« Reply #18 on: June 08, 2019, 06:12:22 PM »

Best for what? There are too many variables. There's also the PGA-103+ that's pretty hot for a few bucks, but easiest place to buy less than 20 pieces is ebay. I've made some nice amps with it, wide band and all, low NF, but they are pretty unstable unless you filter the dickens out of them to the freq you want and you need to work with a microscope. Those one piece gain blocks are pretty nice, but you pay a filter price for them. Through even 70cm discrete stuff is still easy to work with and there's plenty of designs out there. It's all fun.
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