Topband: Slightly OT - amplifier noise

[Mike Waters]

Mike, is there any reason why you tested it above 20 MHz? That's outside
the 1026's specified frequency range.

73, Mike
W0BTU

On Tue, Mar 17, 2020, 9:07 AM Michael Tope <W4EF at dellroy.com> wrote:

> I just happen to have a spare MFJ-1026 at home. I did a real quick test
> using my FT1000MP MK-V while powering the MFJ-1026 from an Astron
> supply. Similar to your results, Steve, I got about a 12 to 14 dB
> increase in the noise floor on 10 meters when the MFJ unit was turned on
> and connected to the MK-V's main antenna input versus when the MFJ unit
> was powered off. This suggests you would have to resort to having
> low-noise pre-amps ahead of each of the MFJ-102x two signal paths and
> the right amount of attenuation after the MFJ-102x's combined output to
> work in your particular very low noise situation.
>
> Since the main antenna path is normally bypassed for transmit, to put a
> pre-amp ahead of the main antenna path you would have to either move
> that MFJ-102x out of the transmit path by putting it in a receive-path
> breakout-loop that is common on many modern transceivers (e.g. between
> RX_OUT and RX_IN jacks), or you would have to have add a dedicated T/R
> bypass scheme for the external main path pre-amp.
>
> FWIW, I also made some gain measurement on my MFJ-1026 (both main and
> sense path gain controls fully clockwise):
>
> Main Antenna Path Gain:
> 10 Meters: 4dB
> 15 Meters: 3dB
>
> Sense Antenna Path Gain (sense-path pre-amp on and internal jumpers set
> for maximum gain):
> 10 Meters: 0.5dB
> 15 Meters: 1.6dB
>
> Difference between having Sense Path Pre-Amp On vs Off:
> 10 Meters: 8dB
> 15 Meters: 9dB
>
> I used an Elecraft XG3 as the signal source and an HP141T to measure
> amplitude.
>
> 73, Mike W4EF...................
>
>