Topband: Slightly OT - amplifier noise

[Michael Tope]

Hi Mike,

I was trying to address the particulars of N2IC's situation which 
involved the higher HF bands (although at this point in the sunspot 
cycle, perhaps I should have included 20 meters).

Reading the manual I have for the MFJ-1026 says "The MFJ-1026 is 
optimized over the range of 1.8 to 30 MHz". Does the MFJ-1025 only go to 
20MHz?

73, Mike W4EF........


On 3/17/2020 10:31 AM, Mike Waters wrote:
> 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...................
>>
>>
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