Post
by Albert H » Fri Jan 26, 2018 10:44 pm
The MMIC broadband amps exemplify the GIGO principle - if you put a dirty signal in, you'll just get a bigger dirty signal out!
On one production exciter board, we used a dual-gate FET VCO, followed by a dual-gate FET amplifier set up as a gain-leveller into an MMIC (MAR6 as I recall). This gave a couple of hundred milliwatts into a ceramic bandpass filter, which emerged - cleaned up - at 100mW which drove a 2N4427 to 1 Watt exactly. The output of the 2N4427 was monitored with an inductively coupled sensing loop, which fed the amplitude information back to the second stage and guaranteed that the RF off the board was exactly 1000mW at any Band II frequency, without any tweaking needed. The levelling loop was incorporated because I found that the MMICs were a bit variable from batch to batch - their gain could vary quite significantly.
"Why is my rig humming?"
"Because it doesn't know the words!" ![Wink ;)](./images/smilies/icon_e_wink.gif)