Low Noise Block Down Converter X-Band mods

Model NJR2117FK

de N6CA May 25, 2004

Virtually without any retuning these block converters will yield a 1.0 to 1.1 dB noise figure and about 27 dB of gain at 10368 MHz.. The only modifications are the removal of the DRO/mixer down converter assembly, the addition of an output connector and feed thru capacitor and jumpering over a 12 GHz band pass filter on the PC board. These mods can be implemented without any test equipment and unless you do something really dumb.......it will work........

These preamplifiers wil not oscillate.... I tried everything I could and it wouldn't do it. that in itself is amazing considering the noise figure, gain and cost; usually under $20 on ebay.

I will get network analyzer plots up shortly as well. Typically the input return loss is about 5 db at 10368 and the addition of a lengthened probe WR75 transition or unmodified WR90 transition will improve it to about 10 to15 db input return loss. There is no difference in noise figure performance with either a WR75 or WR90 transition feeding the amplifier. I plan on redrilling a WR90 chokeless flange for a WR75 hole pattern and going directly into the amplifier.

Thes critters use an 8 volt regulator for the GaAs FET supply pre-regulator. DC power is normally applied thru the F connector which was removed (that was fun)...use a big vise. A 7660 negative voltage generator bug makes the gate bias voltage.

I will get initial pictures up when I get more units. I modified all the ones I had. I modified five of them and they all measured from 1.0 to 1.2 db noise figure. The key to these preamplifiers is they are stable....."hey, I would have worked you if my preamplifier wasn't oscillating......"