Topband: Slightly OT - amplifier noise

[Lloyd - N9LB]

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 at contesting.com] On Behalf Of Steve London
Sent: Monday, March 16, 2020 1:33 PM
To: Guy Olinger K2AV <k2av.guy at gmail.com>
Cc: Topband <topband at 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 at gmail.com 
> <mailto:n2icarrl at 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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