On 5/3/22 09:36, Zach Metzinger wrote:
I've also had good luck with a "plumber's delight" J-pole on 2m and a relatively simple home-brew 2m preamp to set the system noise figure at
One additional link from W6PQL:
"LNAs (preamps) and MMICs" https://www.w6pql.com/LNAs%20(preamps)%20and%20MMICs.htm
His note at the bottom of that page applies to omnidirectional antennas for satellite work. They'll happily pick up interfering sources on the ground, which could then interfere with the signal you're actually trying to receive. You can't do much about signals which are in the band of interest (144-148) without some antenna nulls, but out-of-band interference can be dealt with using filters.
When I installed my 3-d printed Lindenblad in the attic for 70cm, I was surprised at the greatly increased level of noise when I turned it on. It seemed to be a HNA (high noise amplifier)!
Turns out that a nearby water tower, bristling with cellular antennae blasting out digital garbage at 550-700MHz, was overloading the front end of my FT-847 due to the additional gain provided by the LNA. Additional filtering before and after the LNA has solved this problem.
http://www.n0zgo.net/lna/70cm/max2640/70cm_lna_max2640_annotated.jpg
(The BAR64 PIN diodes were added to protect the MAR3-SM+ output gain block when transmitting. Without those, the MAR3 was dead within a few minutes of use at >10W TX.)
--- Zach N0ZGO