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:[email protected]] On Behalf Of Steve London Sent: Monday, March 16, 2020 1:33 PM To: Guy Olinger K2AV <[email protected]> Cc: Topband <[email protected]> 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 <[email protected] > <mailto:[email protected]>> 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 > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > > -- > Sent via Gmail Mobile on my iPhone _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
