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RE: A question about a MMIC preamp



Phil,

The thing to realise with these MMIC's is that they are "JUST" about 50 ohms.... Some are better than others, I think I found the MAR-8 to be the furthest off and 
required the smith chart.... The only other thing I will say is that you may want to think about putting in a Series L/C Combination on your input to make sure when you 
transmit you dont desense the preamp.....

Umm the MAR-6 is a really good unit tho, dont get me wrong...

Altho you might wish to keep away from SO-239/PL-239's connectors as these are pretty evil in my experience, altho that's pretty open to personal preferance and 
opinion....

Here's a design for a 1dB NF & 23dB Gain Preamp using a BF891 at 144MHz.... http://hjem.get2net.dk/ole_nykjaer/oz2oe/bf981/981.html

Definately a nice design if you can etch your own boards and can get a BF891.... Altho a MAR-6 is a good alternative and 50ohms in/out... Hope this helps, to see 
exactly how close you are with those MMIC's you might want to get into the S-Params and get the S11(Input frequency) and the S22(Output Freq) and model them with 
50ohms and see what kind of stock VSWR your getting...

Just my 5cents worth....

Matt Donohoe
m_donohoe@dingoblue.net.au


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