Depending on the exact circuit and device, to measure noise from the device
itself, don’t you have to terminate the inputs to put the normal impedance
on them? The circuits are often designed with the coax Z zero in mind.
73, Guy K2AV
On Mon, Mar 16, 2020 at 12:47 PM Steve London <n2icarrl@gmail.com> wrote:
> This has been a very interesting thread - Thanks for all the input.
>
> Perhaps I have set my expectations too high.
>
> A typical application is on 15 meters, late in the opening, working JA's
> from
> here in SW New Mexico. Absent any local QRN, the band is very quiet. Any
> local
> noise covers the bottom layer of 5 watt JA's calling me.
>
> I did some more testing with the MFJ-1025. With no antennas connected, the
> box
> raises the noise floor about 10 dB, irrespective of the Aux Antenna Gain
> or the
> Main Antenna Gain. I haven't yet tried powering from a battery, to make
> sure the
> power supply isn't the source. Assuming the J310's are quiet, that leaves
> the
> 2N5109 emitter follower, or the back-to-back protection diodes. Might also
> try
> disconnecting the RF sense circuit.
>
> 73,
> Steve, N2IC
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