What gain settings for 2 meters?

Bob N7ZO

With the 6700 on 2 meters, what gain settings activate the ADL5534 and provide the 2.5dB noise figure?

Steve-N5AC

When you go to 20dB you should have a roughly 15.3dB NF.  When you set the preamp to 30dB you will have a NF of 4.3 according to my calculations.  We have a 40dB setting which we have not enabled in software that would give you a NF of 3.7dB, but this seemed like a lot of gain to have in the circuit.  We figured most folks that were really interested in best NF would put a preamp at the antenna rather than rely on the radio -- the feed line is what will **** you at 2m.  You can have a 0.5dB NF in the radio and then put a couple hundred feet of coax in from of it and you've messed that up.

Steve-N5AC

Oh wait, I just realized what you are asking.  You specified the 2.5dB because that is off of the ADL5534 data sheet.  The 2.5dB NF is just for the device under test -- it does not represent the system noise figure.  You must use a cascaded noise figure calculation to determine the system (radio) noise figure.  See references here and here.  This is what I did in the post above.

Bob N7ZO

Hi Steve,

Your first answer was good.  Not having a schematic showing the ADL5534 in-circuit, I just chose the ideal noise figure for the question (somewhat misleadingly in hindsight).  Thank you for the actual numbers.

Steve-N5AC

One other point -- below 6m the ADL5201 is the primary source of gain at 20dB or less in settings (better output IP3).  At 6m and above, preferential treatment goes to the ADL5534 because of its NF.  So a 20dB gain setting on 20m and on 6m actually use a different part.