Having the W7ZOI front end topology of:? ? ?LPF----mixer----6dbAtten----MMIC----IFBPF--- ...
means we have 6dB loss through the diode ring mixer plus 6dB loss through the following attenuator
before the noise figure gets established by the MMIC RF amplifier.
Putting that same MMIC up in front of the mixer means the system noise figure could possibly be
6+6 = 12dB better.? ?W7ZOI knew what he was doing, but I don't fully understand this..
Our front end is dealing with 0 to 250mhz, whereas the W7ZOI SA went for a max of 70mhz.
I doubt that makes the best topology any different.
Any comments?
Jerry, KE7ER
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On Mon, Feb 17, 2020 at 08:59 AM, Jerry Gaffke wrote:
He also has an MMIC after that mixer output's 6dB attenuator to establish the front end noise figure.
A curious placement, up front of the mixer would avoid the 6dB mixer losses,
after the SAW filter would allow the MMIC to not see all the out-of-band signals.
