Mike, thank and these are great data points you've provided. Questions: Was the MFJ-1026 PHASE control set near zero? That could account for the low AUX gain.
*Mike's data* FT1000MP MK-V 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 12 to 14 dB increase in the noise floor on 10 meters when the MFJ unit was turned on *MFJ-1026 MAIN measured noise and calculations* Sherwood Engineering measured the FT-1000 MP MKV Field at -133 dBm in 500 Hz BW. This is -160 dBm in 1 Hz, or 2.2 nV/Hz^0.5. The 12 to 14 dB increase in the noise floor with the MFJ-1026 activated tells us its output noise power is ~13 dB above -133 dBm, or -120 dBm in 500 Hz BW. This is -147 dBm, or *10 nV/H^0.5.* Given the measured AUX path gain of 0.5 dB this tells us the MFJ-1026 AUX input-referred noise is *~9 nV/Hz* on 10 meters. But wait, there's more. In my March 16 email I said "The MFJ-1025 [calculated] output noise is* 9 nV/Hz^0.5."* But, given the MFJ-1026 measured AUX gain of 0.5 dB (10 meters) when I estimated 14 dB AUX gain (20 meters) is a huge discrepancy. This points to the phase shifter circuit attenuating the signal. Might the PHASE control knob be set to 0? This attenuates the AUX path. *Notes* The MFJ-1025 and MJF-1026 use the same circuit with the 1026 adding a whip antenna amplifier. *References* https://www.mfjenterprises.com/support.php?productid=MFJ-1026 http://www.sherweng.com/table.html http://www.sherweng.com/documents/TermsExplainedSherwoodTableofReceiverPerformance-RevF.pdf Dave KH6AQ On Tue, Mar 17, 2020 at 4:07 AM Michael Tope <[email protected]> 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................... > > > > > On 3/16/2020 9:47 AM, Steve London 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 > > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
