Possibly static, nearby lightning, or high levels of TX RF may have damaged one
or more of the semiconductors in your MFJ-1025.
-----Original Message-----
From: Topband [mailto:topband-bounces+lloydberg=tds.net@contesting.com] On
Behalf Of Steve London
Sent: Monday, March 16, 2020 1:33 PM
To: Guy Olinger K2AV <k2av.guy@gmail.com>
Cc: Topband <topband@contesting.com>
Subject: Re: Topband: Slightly OT - amplifier noise
I did that - terminated in 50 ohms.
73,
Steve, N2IC
On 03/16/2020 12:27 PM, Guy Olinger K2AV wrote:
> 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
> <mailto: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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