Re: Topband: Slightly OT - amplifier noise

[Nick Hall-Patch]

See 
http://www.hard-core-dx.com/nordicdx/antenna/special/mfj1026.html 
Jeff; it was a mod.



Nick
VE7DXR

At 17:59 2020-03-20, Jeff wrote:


I thought the 1026 included the BC band, or was that a mod ?

Jeff Reynolds

Mike Waters wrote:

Mike,

I based that on what W8JI states on his webpage, which says 1.8 to 20 MHz.
https://www.w8ji.com/mfj-1025_1026.htm

IIRC, Tom designed that for MFJ.  Maybe that was a typo (on either Tom's
site or in MFJ's manual). Or perhaps the performance drops off to some
degree above 20 MHz. I don't know.

73, Mike
W0BTU

On Wed, Mar 18, 2020, 10:24 AM Michael Tope  wrote:


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.

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Nick Hall-Patch
Victoria, BC
Canada 


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Re: Topband: Slightly OT - amplifier noise

[Jeff]

I thought the 1026 included the BC band, or was that a mod ?

Jeff Reynolds

Mike Waters wrote:

Mike,

I based that on what W8JI states on his webpage, which says 1.8 to 20 MHz.
https://www.w8ji.com/mfj-1025_1026.htm

IIRC, Tom designed that for MFJ.  Maybe that was a typo (on either Tom's
site or in MFJ's manual). Or perhaps the performance drops off to some
degree above 20 MHz. I don't know.

73, Mike
W0BTU

On Wed, Mar 18, 2020, 10:24 AM Michael Tope  wrote:


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.

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Re: Topband: Slightly OT - amplifier noise

[Mike Waters]

Mike,

I based that on what W8JI states on his webpage, which says 1.8 to 20 MHz.
https://www.w8ji.com/mfj-1025_1026.htm

IIRC, Tom designed that for MFJ.  Maybe that was a typo (on either Tom's
site or in MFJ's manual). Or perhaps the performance drops off to some
degree above 20 MHz. I don't know.

73, Mike
W0BTU

On Wed, Mar 18, 2020, 10:24 AM Michael Tope  wrote:

> 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.
>
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Re: Topband: Slightly OT - amplifier noise

[Michael Tope]

Roger,

When you checked for increased noise on 10 and 15 meters, did you have 
your radio set for maximum sensitivity and were the main and AUX input 
ports of the MFJ-1025 terminated with 50 ohms (or at least not connected 
to any outside antenna)?


73, Mike W4EF.

On 3/17/2020 11:18 AM, Roger Kennedy wrote:

Having just read some of these posts, I just did a few tests on my MFJ-1025.
(bought mine second-hand very cheap - a lot of people buy these thinking
they will get rid of any noise!)

I modified it to become a 1026 . . . you definitely need the extra pre-amp
for the "Noise Antenna", especially on 160m - fortunately they use the same
PCB for both versions, so you can easily add their extra preamp circuit
design on the PCB.

I normally only use mine on 160m . . . but just did a test on 15m & 10m . .
. it adds no noticeable noise whatsoever !

So I think the OP's must be faulty . . perhaps powering it by a noisy PSU?

Roger G3YRO



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Re: 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  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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Re: Topband: Slightly OT - amplifier noise

[Michael Tope]

You were spot on, Dave. Thanks for the suggestion. I rechecked the 
numbers this morning and the AUX (i.e. sense antenna path) gain varies 
about 2dB as a function of where the phase control is set. It appears I 
had the phase control sitting in the worst-case minimum gain position 
(apparently quite by accident) which seems to occur around "8" or "9". 
The maximum gain occurs with the control fully clockwise at "10", so 
there is a lot of variation between "7" and "10".  Between a phase 
control setting of "0" and "7" the change in the sense path gain is much 
smaller. When you flip the phase polarity, there is a small amount of 
gain change. The maximum gain numbers are pretty close to the main 
antenna path numbers.


10 Meters: 2.8dB (0.5dB min)
15 Meters: 4.6dB (2.6dB min) [note: the 1.6dB number previously reported 
may be an error]


Please take the decimal point with a grain of salt. These are not lab 
grade measurements [think quick and dirty order-of-magnitude measurement 
done with a fair amount of haste]. The cables and adapters I used should 
probably be thrown away and replaced with better quality parts and it's 
possible Nixon was still president the last time the 141T was calibrated 
to NIST standards :-)


73, Mike W4EF.

On 3/17/2020 9:56 AM, Dave Cuthbert wrote:

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 > 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
> 

Re: Topband: Slightly OT - amplifier noise

[Mike Waters]

Roger,

I didn't realize that the 1025 (which is what I have) didn't have a preamp
on the auxiliary (noise) antenna input!

I chose the 1025 over the 1026 because I did not want the small whip
antenna, which only works well if you have RFI close to it. If I would have
realized that the 1026 circuit had a preamp, I might have purchased that
instead.

But when I do use it (very rarely), I almost always use a homebrew W7IUV
preamp to feed the noise antenna input, with no issues.

What kind of preamp did you add to your 1025?

73, Mike
W0BTU

On Tue, Mar 17, 2020, 1:18 PM Roger Kennedy 
wrote:

>
> Having just read some of these posts, I just did a few tests on my
> MFJ-1025.
> (bought mine second-hand very cheap - a lot of people buy these thinking
> they will get rid of any noise!)
>
> I modified it to become a 1026 . . . you definitely need the extra pre-amp
> for the "Noise Antenna", especially on 160m - fortunately they use the same
> PCB for both versions, so you can easily add their extra preamp circuit
> design on the PCB.
>
> I normally only use mine on 160m . . . but just did a test on 15m & 10m . .
> . it adds no noticeable noise whatsoever !
>
> So I think the OP's must be faulty . . perhaps powering it by a noisy PSU?
>
> Roger G3YRO
>
>
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Re: Topband: Slightly OT - amplifier noise

[Richard (Rick) Karlquist]

On 3/14/2020 4:07 PM, Jim Brown wrote:


Another good advantage to the electronic schemes is that you don't have 
to go outside to rotate them when the noise that's bothering you is 
coming from a different direction.


73, Jim



That is an interesting idea.

I have been trying to figure out how I could phase two verticals
so as to have a null(s) with steerable azimuth, but I'm stumped.
Using EZNEC modeling two 30 foot monopoles 70 feet apart, I can
drive them 180° out of phase and get a figure 8 pattern like
a broadside loop.  I can drive them 135° out of phase and get
a cardioid pattern that doesn't have a sharp null, but rather
rejects everything off the back of the array.  Other angles
produce variations on these patterns, but not a steerable
null.

I could imagine that an array of 3 or 4 or 6 antennas in a circle
might produce steerable nulls.

Am I missing something?

73
Rick N6RK

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Re: Topband: Slightly OT - amplifier noise

[Jim Brown]

On 3/17/2020 10:26 AM, Mike Waters wrote:

That being the case, shouldn't noise tests be done on 160 or 80 meters,
rather than 10 or 15 meters?


In my tests of my NCC-1, I found it pretty useless above 40M. It 
accommodates optional preamps; it's driven by a K9AY 8x4 matrix 
switcher, which includes his preamps (switchable).


73, Jim K9YC
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Re: 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  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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Re: Topband: Slightly OT - amplifier noise

[Mike Waters]

Tom Rauch, W8JI has a nice webpage dedicated to the MFJ-1025/1026 at
https://www.w8ji.com/mfj-1025_1026.htm.

A few relevant excerpts follow.

"The only drawback of the higher noise floor of the MFJ-1025/1026 is you *must
place it after any amplifiers used with low-level low-noise antennas*. The
MFJ-1025/1026 noise floor is typically around 14dB."


"The MFJ1025 series, despite being manufactured as inexpensively as
possible, outperforms any other unit I have tested (by a large margin) over
its intended *frequency range of 1.8-20 MHz*.  The exception is the DX
Engineering NCC-1..."

That being the case, shouldn't noise tests be done on 160 or 80 meters,
rather than 10 or 15 meters?

73, Mike
W0BTU
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Re: Topband: Slightly OT - amplifier noise

[Dave Cuthbert]

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  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
>
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> Reflector
>
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Re: Topband: Slightly OT - amplifier noise

[sawyered]

I remember having some experience with that MFJ-1026 a number of years ago
and found the trade off of increased noise floor vs cancelling not worth the
effort.  Trading one evil for another evil.  Obviously, when confronted with
noise mitigation, everything is on the table.

 

Ed  N1UR

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Re: Topband: Slightly OT - amplifier noise

[Michael Tope]

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
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Reflector


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Re: Topband: Slightly OT - amplifier noise

[Lee STRAHAN]

Hi Dave,
In my experience that is not a typical Norton amplifier gain . Most would be 
considerably in excess of that at 11  or 19 dB. They can run from 5 to 19 dB or 
so but what would be the purpose of only putting 5 dB there with an expensive 
amplifier configuration?  The ones I use are 11 dB gain. Just my $.02
Lee K7TJR

From: Dave Cuthbert 
Sent: Monday, March 16, 2020 3:05 PM
To: Lee STRAHAN 
Cc: topband@contesting.com
Subject: Re: Topband: Slightly OT - amplifier noise

Circuit gain is accounted for in my calculations. I ran a sim of the input amp 
and could get it to work with gains from 0.5 to 2 using different transformer 
ratios. So, I think the gain-of-2 I used is good enough.

On Mon, Mar 16, 2020 at 11:32 AM Lee STRAHAN 
mailto:k7...@msn.com>> wrote:
  Don’t forget there is gain in the signal paths. That first AUX input stage is 
a Norton configuration amp with gain controlled by the unknown transformer 
ratios. The two J-310's that sum the signals also appear to have a few dB gain. 
A full analysis of the circuit is necessary to derive what the insertion gain 
of this device would be. Or a measurement might be in order with gain pots at 
max. It could be amplified input device noise at the output.
Lee   K7TJR

-Original Message-
From: Topband 
mailto:msn@contesting.com>> 
On Behalf Of Dave Cuthbert
Sent: Monday, March 16, 2020 2:05 PM
To: n...@arrl.net<mailto:n...@arrl.net>
Cc: Topband mailto:topband@contesting.com>>; Guy 
Olinger K2AV mailto:k2av....@gmail.com>>
Subject: Re: Topband: Slightly OT - amplifier noise

Steve,

I performed a hand calculation of the MFJ-1025 14 MHz noise and it's (only)
9 nV/Hz^0.5, or 0.2 uV in 500 Hz. This is -120 dBm, or S-1. But you measure
S-4 noise. What is going on?

Questions to determine what is going on:

Question 1) What model is the radio?
Question 2: What bandwidth is the noise measured with?
Question 3: What band?
Question 4: What does the radio  measure connected to the MFJ-1025 but with 
the MFJ powered OFF?


*MFJ-1025 termination *
With the two MFJ-1025 antenna terminals left open the two JFET inputs are 
terminated in 0-78 ohms depending on the gain pot settings. Note that gain pots 
reduce the signal but not JFET noise and cutting the gain degrades the S/N 
ratio. With the gain pots at maximum the unterminated input noise from the 
resistors is (only) 1.1 nV/Hz^0.5.

*MFJ-1025 noise calculations*
Let's add up all the noise sources and derive the 14 MHz noise.

*Q4 output buffer*
   Q5 voltage gain, 1
   1 nV/Hz^0.5 transistor (my estimate; I can calculate it but it's low enough 
to just call it 1 nV/Hz^0.5)
   1.9 nV/Hz^0.5 for R8 (220 ohms)
   Total input noise 2.2 nV/Hz^0.5 (the transistor noise is my estimate)
   Total output noise 2.2 nV/Hz^0.5

*Q5, Q6 active combiner*
   Q5 voltage gain, 1.1
   R9||R26, 1.1 nV/Hz^0.5
   Q5 gate, 0.6 nV/Hz^0.5
   Input noise, 1.3 nV/Hz^0.5
   Output noise, 1.4 nV/Hz^0.5

   Q6 voltage gain, 2.3
   R13, 1.9 nV/Hz^0.5
   Q6 gate, 0.6 nV/Hz^0.5
   Input noise, 2.0 nV/Hz^0.5
   Output noise, 4.6 nV/Hz^0.5

   Q5 + Q6 noise
   Output noise, 4.8 nV/Hz^0.5

   *Q7 phase splitter*
   Q7 voltage gain, 1
   Q7 gate, 0.6 nV/Hz^0.5
   R13, 1.9 nV/Hz^0.5
   Output noise, 2.0 nV/Hz

   *Q8 AUX amp *
   Q8 voltage gain, 2 (that's a guess)
   R20||R27, 1.1 nV/Hz^0.5
   Q8 gate, 0.6 nV/Hz^0.5
   Input noise, 1.3 nV/Hz^0.5
   Output noise, 2.6 nV/Hz^0.5

*Adding it up*
The noise into Q6 is the AUX amp (2.6 nV/Hz^0.5) + the phase splitter (2.0
nV/Hz) = 3.3 nV/Hz^0.5

The noise out of Q6 is X2.3 the input noise = 7.5 nV/Hz The noise out of Q5 is 
4.8 nV/Hz^0.5 Adding two these together the noise into Q4 is 8.9 nV/Hz Add 1 
nV/Hz^0.5  for Q1 and we have 9.0 nV/Hz

The MFJ-1025 *output noise is 9 nV/Hz^0.5*

In a 500 Hz BW this is 200 nV, or 48 dB below S-9. *This is S-1*.
The AUX-referred noise is ~1.7 nV/Hz^0.5 The MAIN-referred noise is ~8 nV/Hz^0.5

*12V Power is well decoupled*
The 12V power is well decoupled with 14 MHz PS rejection ratio of 110 dB.
This is calculated for bypass cap C7 having 10 nH lead inductance. So, I don't 
see that noise on the 12V source makes a difference.

*LTSpice J310 noise model issue*
I ran sims of a J310 JFET in a simple source-follower circuit and LTSpice 
reports noise that is so far off it's unusable. Instead I use a claimed noise 
figure of 3 dB. If I use the specified 100 Hz noise of 10 nV/Hz^0.5 the output 
noise rises enough to make S-4 noise. But, I believe the 100 Hz noise is below 
the J310 1/f frequency and is much higher than the HF noise.
I think I can calculate the 1/f frequency to make sure. About 10 years ago I 
designed a test setup to measure MOSFET noise and ran thru the calculations for 
1/f and noise.

*References*
MFJ-1025 manual with schematic:
https://www.mfjenterprises.com/support.php?productid=MFJ-1025

J310 datasheet:
http://pdf.datasheetcatalog.com/datasheet_pdf/intersil/J308_to_J310.pdf

Re: Topband: Slightly OT - amplifier noise

[Dave Cuthbert]

Circuit gain is accounted for in my calculations. I ran a sim of the input
amp and could get it to work with gains from 0.5 to 2 using different
transformer ratios. So, I think the gain-of-2 I used is good enough.

On Mon, Mar 16, 2020 at 11:32 AM Lee STRAHAN  wrote:

>   Don’t forget there is gain in the signal paths. That first AUX input
> stage is a Norton configuration amp with gain controlled by the unknown
> transformer ratios. The two J-310's that sum the signals also appear to
> have a few dB gain. A full analysis of the circuit is necessary to derive
> what the insertion gain of this device would be. Or a measurement might be
> in order with gain pots at max. It could be amplified input device noise at
> the output.
> Lee   K7TJR
>
> -Original Message-
> From: Topband  On Behalf Of
> Dave Cuthbert
> Sent: Monday, March 16, 2020 2:05 PM
> To: n...@arrl.net
> Cc: Topband ; Guy Olinger K2AV  >
> Subject: Re: Topband: Slightly OT - amplifier noise
>
> Steve,
>
> I performed a hand calculation of the MFJ-1025 14 MHz noise and it's (only)
> 9 nV/Hz^0.5, or 0.2 uV in 500 Hz. This is -120 dBm, or S-1. But you measure
> S-4 noise. What is going on?
>
> Questions to determine what is going on:
>
> Question 1) What model is the radio?
> Question 2: What bandwidth is the noise measured with?
> Question 3: What band?
> Question 4: What does the radio  measure connected to the MFJ-1025 but
> with the MFJ powered OFF?
>
>
> *MFJ-1025 termination *
> With the two MFJ-1025 antenna terminals left open the two JFET inputs are
> terminated in 0-78 ohms depending on the gain pot settings. Note that gain
> pots reduce the signal but not JFET noise and cutting the gain degrades the
> S/N ratio. With the gain pots at maximum the unterminated input noise from
> the resistors is (only) 1.1 nV/Hz^0.5.
>
> *MFJ-1025 noise calculations*
> Let's add up all the noise sources and derive the 14 MHz noise.
>
> *Q4 output buffer*
>Q5 voltage gain, 1
>1 nV/Hz^0.5 transistor (my estimate; I can calculate it but it's low
> enough to just call it 1 nV/Hz^0.5)
>1.9 nV/Hz^0.5 for R8 (220 ohms)
>Total input noise 2.2 nV/Hz^0.5 (the transistor noise is my estimate)
>Total output noise 2.2 nV/Hz^0.5
>
> *Q5, Q6 active combiner*
>Q5 voltage gain, 1.1
>R9||R26, 1.1 nV/Hz^0.5
>Q5 gate, 0.6 nV/Hz^0.5
>Input noise, 1.3 nV/Hz^0.5
>Output noise, 1.4 nV/Hz^0.5
>
>Q6 voltage gain, 2.3
>R13, 1.9 nV/Hz^0.5
>Q6 gate, 0.6 nV/Hz^0.5
>Input noise, 2.0 nV/Hz^0.5
>Output noise, 4.6 nV/Hz^0.5
>
>Q5 + Q6 noise
>Output noise, 4.8 nV/Hz^0.5
>
>*Q7 phase splitter*
>Q7 voltage gain, 1
>Q7 gate, 0.6 nV/Hz^0.5
>R13, 1.9 nV/Hz^0.5
>Output noise, 2.0 nV/Hz
>
>*Q8 AUX amp *
>Q8 voltage gain, 2 (that's a guess)
>R20||R27, 1.1 nV/Hz^0.5
>Q8 gate, 0.6 nV/Hz^0.5
>Input noise, 1.3 nV/Hz^0.5
>Output noise, 2.6 nV/Hz^0.5
>
> *Adding it up*
> The noise into Q6 is the AUX amp (2.6 nV/Hz^0.5) + the phase splitter (2.0
> nV/Hz) = 3.3 nV/Hz^0.5
>
> The noise out of Q6 is X2.3 the input noise = 7.5 nV/Hz The noise out of
> Q5 is 4.8 nV/Hz^0.5 Adding two these together the noise into Q4 is 8.9
> nV/Hz Add 1 nV/Hz^0.5  for Q1 and we have 9.0 nV/Hz
>
> The MFJ-1025 *output noise is 9 nV/Hz^0.5*
>
> In a 500 Hz BW this is 200 nV, or 48 dB below S-9. *This is S-1*.
> The AUX-referred noise is ~1.7 nV/Hz^0.5 The MAIN-referred noise is ~8
> nV/Hz^0.5
>
> *12V Power is well decoupled*
> The 12V power is well decoupled with 14 MHz PS rejection ratio of 110 dB.
> This is calculated for bypass cap C7 having 10 nH lead inductance. So, I
> don't see that noise on the 12V source makes a difference.
>
> *LTSpice J310 noise model issue*
> I ran sims of a J310 JFET in a simple source-follower circuit and LTSpice
> reports noise that is so far off it's unusable. Instead I use a claimed
> noise figure of 3 dB. If I use the specified 100 Hz noise of 10 nV/Hz^0.5
> the output noise rises enough to make S-4 noise. But, I believe the 100 Hz
> noise is below the J310 1/f frequency and is much higher than the HF noise.
> I think I can calculate the 1/f frequency to make sure. About 10 years ago
> I designed a test setup to measure MOSFET noise and ran thru the
> calculations for 1/f and noise.
>
> *References*
> MFJ-1025 manual with schematic:
> https://www.mfjenterprises.com/support.php?productid=MFJ-1025
>
> J310 datasheet:
> http://pdf.datasheetcatalog.com/datasheet_pdf/intersil/J308_to_J310.pdf
>
> J310 RF amp noise figure: http://receiverforjupiter.tripod.com/rfamp.htm
>
> Dave KH6AQ
>
>
&g

Re: Topband: Slightly OT - amplifier noise

[Lee STRAHAN]

  Don’t forget there is gain in the signal paths. That first AUX input stage is 
a Norton configuration amp with gain controlled by the unknown transformer 
ratios. The two J-310's that sum the signals also appear to have a few dB gain. 
A full analysis of the circuit is necessary to derive what the insertion gain 
of this device would be. Or a measurement might be in order with gain pots at 
max. It could be amplified input device noise at the output.
Lee   K7TJR

-Original Message-
From: Topband  On Behalf Of Dave 
Cuthbert
Sent: Monday, March 16, 2020 2:05 PM
To: n...@arrl.net
Cc: Topband ; Guy Olinger K2AV 
Subject: Re: Topband: Slightly OT - amplifier noise

Steve,

I performed a hand calculation of the MFJ-1025 14 MHz noise and it's (only)
9 nV/Hz^0.5, or 0.2 uV in 500 Hz. This is -120 dBm, or S-1. But you measure
S-4 noise. What is going on?

Questions to determine what is going on:

Question 1) What model is the radio?
Question 2: What bandwidth is the noise measured with?
Question 3: What band?
Question 4: What does the radio  measure connected to the MFJ-1025 but with 
the MFJ powered OFF?


*MFJ-1025 termination *
With the two MFJ-1025 antenna terminals left open the two JFET inputs are 
terminated in 0-78 ohms depending on the gain pot settings. Note that gain pots 
reduce the signal but not JFET noise and cutting the gain degrades the S/N 
ratio. With the gain pots at maximum the unterminated input noise from the 
resistors is (only) 1.1 nV/Hz^0.5.

*MFJ-1025 noise calculations*
Let's add up all the noise sources and derive the 14 MHz noise.

*Q4 output buffer*
   Q5 voltage gain, 1
   1 nV/Hz^0.5 transistor (my estimate; I can calculate it but it's low enough 
to just call it 1 nV/Hz^0.5)
   1.9 nV/Hz^0.5 for R8 (220 ohms)
   Total input noise 2.2 nV/Hz^0.5 (the transistor noise is my estimate)
   Total output noise 2.2 nV/Hz^0.5

*Q5, Q6 active combiner*
   Q5 voltage gain, 1.1
   R9||R26, 1.1 nV/Hz^0.5
   Q5 gate, 0.6 nV/Hz^0.5
   Input noise, 1.3 nV/Hz^0.5
   Output noise, 1.4 nV/Hz^0.5

   Q6 voltage gain, 2.3
   R13, 1.9 nV/Hz^0.5
   Q6 gate, 0.6 nV/Hz^0.5
   Input noise, 2.0 nV/Hz^0.5
   Output noise, 4.6 nV/Hz^0.5

   Q5 + Q6 noise
   Output noise, 4.8 nV/Hz^0.5

   *Q7 phase splitter*
   Q7 voltage gain, 1
   Q7 gate, 0.6 nV/Hz^0.5
   R13, 1.9 nV/Hz^0.5
   Output noise, 2.0 nV/Hz

   *Q8 AUX amp *
   Q8 voltage gain, 2 (that's a guess)
   R20||R27, 1.1 nV/Hz^0.5
   Q8 gate, 0.6 nV/Hz^0.5
   Input noise, 1.3 nV/Hz^0.5
   Output noise, 2.6 nV/Hz^0.5

*Adding it up*
The noise into Q6 is the AUX amp (2.6 nV/Hz^0.5) + the phase splitter (2.0
nV/Hz) = 3.3 nV/Hz^0.5

The noise out of Q6 is X2.3 the input noise = 7.5 nV/Hz The noise out of Q5 is 
4.8 nV/Hz^0.5 Adding two these together the noise into Q4 is 8.9 nV/Hz Add 1 
nV/Hz^0.5  for Q1 and we have 9.0 nV/Hz

The MFJ-1025 *output noise is 9 nV/Hz^0.5*

In a 500 Hz BW this is 200 nV, or 48 dB below S-9. *This is S-1*.
The AUX-referred noise is ~1.7 nV/Hz^0.5 The MAIN-referred noise is ~8 nV/Hz^0.5

*12V Power is well decoupled*
The 12V power is well decoupled with 14 MHz PS rejection ratio of 110 dB.
This is calculated for bypass cap C7 having 10 nH lead inductance. So, I don't 
see that noise on the 12V source makes a difference.

*LTSpice J310 noise model issue*
I ran sims of a J310 JFET in a simple source-follower circuit and LTSpice 
reports noise that is so far off it's unusable. Instead I use a claimed noise 
figure of 3 dB. If I use the specified 100 Hz noise of 10 nV/Hz^0.5 the output 
noise rises enough to make S-4 noise. But, I believe the 100 Hz noise is below 
the J310 1/f frequency and is much higher than the HF noise.
I think I can calculate the 1/f frequency to make sure. About 10 years ago I 
designed a test setup to measure MOSFET noise and ran thru the calculations for 
1/f and noise.

*References*
MFJ-1025 manual with schematic:
https://www.mfjenterprises.com/support.php?productid=MFJ-1025

J310 datasheet:
http://pdf.datasheetcatalog.com/datasheet_pdf/intersil/J308_to_J310.pdf

J310 RF amp noise figure: http://receiverforjupiter.tripod.com/rfamp.htm

Dave KH6AQ


On Mon, Mar 16, 2020 at 8:33 AM Steve London  wrote:

> 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  > <mailto:n2ica...@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

Re: Topband: Slightly OT - amplifier noise

[Dave Cuthbert]

Steve,

I performed a hand calculation of the MFJ-1025 14 MHz noise and it's (only)
9 nV/Hz^0.5, or 0.2 uV in 500 Hz. This is -120 dBm, or S-1. But you measure
S-4 noise. What is going on?

Questions to determine what is going on:

Question 1) What model is the radio?
Question 2: What bandwidth is the noise measured with?
Question 3: What band?
Question 4: What does the radio  measure connected to the MFJ-1025 but
with the MFJ powered OFF?


*MFJ-1025 termination *
With the two MFJ-1025 antenna terminals left open the two JFET inputs are
terminated in 0-78 ohms depending on the gain pot settings. Note that gain
pots reduce the signal but not JFET noise and cutting the gain degrades the
S/N ratio. With the gain pots at maximum the unterminated input noise from
the resistors is (only) 1.1 nV/Hz^0.5.

*MFJ-1025 noise calculations*
Let's add up all the noise sources and derive the 14 MHz noise.

*Q4 output buffer*
   Q5 voltage gain, 1
   1 nV/Hz^0.5 transistor (my estimate; I can calculate it but it's low
enough to just call it 1 nV/Hz^0.5)
   1.9 nV/Hz^0.5 for R8 (220 ohms)
   Total input noise 2.2 nV/Hz^0.5 (the transistor noise is my estimate)
   Total output noise 2.2 nV/Hz^0.5

*Q5, Q6 active combiner*
   Q5 voltage gain, 1.1
   R9||R26, 1.1 nV/Hz^0.5
   Q5 gate, 0.6 nV/Hz^0.5
   Input noise, 1.3 nV/Hz^0.5
   Output noise, 1.4 nV/Hz^0.5

   Q6 voltage gain, 2.3
   R13, 1.9 nV/Hz^0.5
   Q6 gate, 0.6 nV/Hz^0.5
   Input noise, 2.0 nV/Hz^0.5
   Output noise, 4.6 nV/Hz^0.5

   Q5 + Q6 noise
   Output noise, 4.8 nV/Hz^0.5

   *Q7 phase splitter*
   Q7 voltage gain, 1
   Q7 gate, 0.6 nV/Hz^0.5
   R13, 1.9 nV/Hz^0.5
   Output noise, 2.0 nV/Hz

   *Q8 AUX amp *
   Q8 voltage gain, 2 (that's a guess)
   R20||R27, 1.1 nV/Hz^0.5
   Q8 gate, 0.6 nV/Hz^0.5
   Input noise, 1.3 nV/Hz^0.5
   Output noise, 2.6 nV/Hz^0.5

*Adding it up*
The noise into Q6 is the AUX amp (2.6 nV/Hz^0.5) + the phase splitter (2.0
nV/Hz) = 3.3 nV/Hz^0.5

The noise out of Q6 is X2.3 the input noise = 7.5 nV/Hz
The noise out of Q5 is 4.8 nV/Hz^0.5
Adding two these together the noise into Q4 is 8.9 nV/Hz
Add 1 nV/Hz^0.5  for Q1 and we have 9.0 nV/Hz

The MFJ-1025 *output noise is 9 nV/Hz^0.5*

In a 500 Hz BW this is 200 nV, or 48 dB below S-9. *This is S-1*.
The AUX-referred noise is ~1.7 nV/Hz^0.5
The MAIN-referred noise is ~8 nV/Hz^0.5

*12V Power is well decoupled*
The 12V power is well decoupled with 14 MHz PS rejection ratio of 110 dB.
This is calculated for bypass cap C7 having 10 nH lead inductance. So, I
don't see that noise on the 12V source makes a difference.

*LTSpice J310 noise model issue*
I ran sims of a J310 JFET in a simple source-follower circuit and LTSpice
reports noise that is so far off it's unusable. Instead I use a claimed
noise figure of 3 dB. If I use the specified 100 Hz noise of 10 nV/Hz^0.5
the output noise rises enough to make S-4 noise. But, I believe the 100 Hz
noise is below the J310 1/f frequency and is much higher than the HF noise.
I think I can calculate the 1/f frequency to make sure. About 10 years ago
I designed a test setup to measure MOSFET noise and ran thru the
calculations for 1/f and noise.

*References*
MFJ-1025 manual with schematic:
https://www.mfjenterprises.com/support.php?productid=MFJ-1025

J310 datasheet:
http://pdf.datasheetcatalog.com/datasheet_pdf/intersil/J308_to_J310.pdf

J310 RF amp noise figure: http://receiverforjupiter.tripod.com/rfamp.htm

Dave KH6AQ


On Mon, Mar 16, 2020 at 8:33 AM Steve London  wrote:

> 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  > > 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: 

Re: Topband: Slightly OT - amplifier noise

[Mike Waters]

This is what I have been thinking all along.

On Mon, Mar 16, 2020, 1:47 PM Lloyd - N9LB  wrote:

> Possibly static, nearby lightning, or high levels of TX RF may have
> damaged one or more of the semiconductors in your MFJ-1025.
>
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Re: 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@contesting.com] On 
Behalf Of Steve London
Sent: Monday, March 16, 2020 1:33 PM
To: Guy Olinger K2AV 
Cc: Topband 
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  <mailto:n2ica...@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
> _
> 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

Re: Topband: Slightly OT - amplifier noise

[Steve London]

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 > 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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Re: Topband: Slightly OT - amplifier noise

[Guy Olinger K2AV]

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  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
>
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Re: Topband: Slightly OT - amplifier noise

[Steve London]

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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Re: Topband: Slightly OT - amplifier noise

[Ken Claerbout]

A couple of issues I see.  It depends which direction(s) the noise and
desired signal are coming from.  You may null the noise and signal.
Also, the loop is bi-directional.

I've been playing with a DX Engineering RF-PRO-1B at ET3AA and it
works.  Thanks to Tim and the gang for their support.  But there is a
lot of noise and not being able to null everything except the desired
direction I suspect is an issue.

Our noise is close in, so I have some upgrades in place using a Hi-Z 4
square and NCC-2 with a "noise" antenna as Frank mentions.
Unfortunately the next thing I need to do after I send this, is to
cancel my reservation for the 27th of this month.  Africa looks like a
pretty safe place Covid-19 wise at the moment.  But one look at the
long lines at immigration did me in.  I don't have the patience for
that.

73
Ken K4ZW


On Sat, Mar 14, 2020 at 11:43 PM  wrote:
>
>
> Hi Rick,
>
>
>
> A noise receiving antenna close to a noise source is used in conjunction
> with a higher performance receiving antenna such as a Beverage or an
> array of short verticals and a passive or active noise canceller.
>
>
>
> A small loop antenna provides a mechanically steerable null off of both
> sides of the loop. Null beamwidth is just a few degrees at the 3 dB
> points, otherwise a small loop is an omni-directional receiving antenna.
> Simply turn the loop to minimize the interfering noise signal strength.
>
>
> The smaller the loop, the deeper the null depth but the smaller the signal
> strength of desired signals. A small loop antenna requires a low noise
> high gain pre-amp directly at its feed point for optimum sensitivity.
>
>
> A small loop antenna should be close to ground for optimum null depth.
> Horizontally polarized skywave signals penetrate the nulls if a small
> 160 meter loop antenna is much higher than than about ten feet above the 
> ground
>
>
> On 160 meters a small loop antenna provides:
> - a 30 dB null off each side of a 5 foot diameter loop.
> - a 25 dB null off each side of a 10 foot diameter loop, or
> - a 20 dB null off each side of a 17 foot diameter loop
>
>
> 73
>
> Frank
> W3LPL
>
>
>
>
>
>
>
>
> - Original Message -----
>
> From: "Richard (Rick) Karlquist" 
> To: "Dave Cuthbert" , n...@arrl.net
> Cc: "Topband" 
> Sent: Saturday, March 14, 2020 10:17:59 PM
> Subject: Re: Topband: Slightly OT - amplifier noise
>
>
> I am trying to understand what these noise cancelling
> schemes do that couldn't be done with a simple loop
> (rotating the loop until the noise drops into one of
> the null directions). You can easily prove to yourself
> with a hand held AM BCB receiver equipped with a ferrite
> bar antenna that even the worst power line noise can
> almost always be greatly suppressed by properly rotating
> the receiver. Similarly, I have had good luck with
> small tuned loops (10 feet perimeter) nulling power
> line noise. Smaller loops seem to have deeper nulls.
>
> It is critical to keep loops away from your other antennas
> and power wiring. Otherwise, they will not exhibit a
> good null.
>
> Rick N6RK
> _
> Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
>
> _
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Re: Topband: Slightly OT - amplifier noise

[donovanf]

Hi Rick, 



A noise receiving antenna close to a noise source is used in conjunction 
with a higher performance receiving antenna such as a Beverage or an 
array of short verticals and a passive or active noise canceller. 



A small loop antenna provides a mechanically steerable null off of both 
sides of the loop. Null beamwidth is just a few degrees at the 3 dB 
points, otherwise a small loop is an omni-directional receiving antenna. 
Simply turn the loop to minimize the interfering noise signal strength. 


The smaller the loop, the deeper the null depth but the smaller the signal 
strength of desired signals. A small loop antenna requires a low noise 
high gain pre-amp directly at its feed point for optimum sensitivity. 


A small loop antenna should be close to ground for optimum null depth. 
Horizontally polarized skywave signals penetrate the nulls if a small 
160 meter loop antenna is much higher than than about ten feet above the ground 


On 160 meters a small loop antenna provides: 
- a 30 dB null off each side of a 5 foot diameter loop. 
- a 25 dB null off each side of a 10 foot diameter loop, or 
- a 20 dB null off each side of a 17 foot diameter loop 


73 

Frank 
W3LPL 








- Original Message -

From: "Richard (Rick) Karlquist"  
To: "Dave Cuthbert" , n...@arrl.net 
Cc: "Topband"  
Sent: Saturday, March 14, 2020 10:17:59 PM 
Subject: Re: Topband: Slightly OT - amplifier noise 


I am trying to understand what these noise cancelling 
schemes do that couldn't be done with a simple loop 
(rotating the loop until the noise drops into one of 
the null directions). You can easily prove to yourself 
with a hand held AM BCB receiver equipped with a ferrite 
bar antenna that even the worst power line noise can 
almost always be greatly suppressed by properly rotating 
the receiver. Similarly, I have had good luck with 
small tuned loops (10 feet perimeter) nulling power 
line noise. Smaller loops seem to have deeper nulls. 

It is critical to keep loops away from your other antennas 
and power wiring. Otherwise, they will not exhibit a 
good null. 

Rick N6RK 
_ 
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Re: Topband: Slightly OT - amplifier noise

[Richard (Rick) Karlquist]

On 3/14/2020 3:27 PM, Greg - ZL3IX wrote:
I used one of these systems (homebrew WA1ION) for a  couple of years in 
the early 2000s. My problem was a speed-controlled water pump (local 
water authority) very close to my QTH. The pump was in the same 
direction as most of the wanted DX, so a nulling loop didn't work.




Great explanation.  Now I know what these canceling boxes are good for.
I have a troublesome power pole about 100 ft off the corner of
my property.  I could put a sense antenna up in that corner
and use it with my ANC-4.

73
Rick N6RK

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Re: Topband: Slightly OT - amplifier noise

[Jim Brown]

On 3/14/2020 3:17 PM, Richard (Rick) Karlquist wrote:

I am trying to understand what these noise cancelling
schemes do that couldn't be done with a simple loop
(rotating the loop until the noise drops into one of
the null directions).


I can't find the very recent email where this example was cited to quote 
it, but the op had a noise source coming from the same direction as 
desired signals, so he placed a sense antenna very close to the source.


Another good advantage to the electronic schemes is that you don't have 
to go outside to rotate them when the noise that's bothering you is 
coming from a different direction.


73, Jim


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Re: Topband: Slightly OT - amplifier noise

[Greg - ZL3IX]

I used one of these systems (homebrew WA1ION) for a  couple of years in 
the early 2000s. My problem was a speed-controlled water pump (local 
water authority) very close to my QTH. The pump was in the same 
direction as most of the wanted DX, so a nulling loop didn't work.


What I did was to erect a sense antenna as close as possible to the 
noise source and run the noise signal via a coax to the WA1ION box in my 
shack. Since the sense antenna was close to the noise source, the noise 
was very loud and could be (had to be ) attenuated before summing with 
the signal from the main antenna. The wanted signals picked up by the 
sense antenna were also therefore attenuated, and did not subtract from 
the wanted signals picked up by the main antenna.


I was able to achieve a very useful 10-12 dB of S/N improvement using 
this technique.


73, Greg, ZL3IX

On 2020-03-15 11:17, Richard (Rick) Karlquist wrote:


I am trying to understand what these noise cancelling
schemes do that couldn't be done with a simple loop
(rotating the loop until the noise drops into one of
the null directions).

Rick N6RK
_
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Reflector


_
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Re: Topband: Slightly OT - amplifier noise

[Richard (Rick) Karlquist]

I am trying to understand what these noise cancelling
schemes do that couldn't be done with a simple loop
(rotating the loop until the noise drops into one of
the null directions).  You can easily prove to yourself
with a hand held AM BCB receiver equipped with a ferrite
bar antenna that even the worst power line noise can
almost always be greatly suppressed by properly rotating
the receiver.  Similarly, I have had good luck with
small tuned loops (10 feet perimeter) nulling power
line noise.  Smaller loops seem to have deeper nulls.

It is critical to keep loops away from your other antennas
and power wiring.  Otherwise, they will not exhibit a
good null.

Rick N6RK
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Re: Topband: Slightly OT - amplifier noise

[Michael Tope]

Dave is that -112 dBm you calculated the output referred noise? If so, 
what is the gain behind it?


Thanks,

73, Mike W4EF...

On 3/14/2020 2:13 PM, Dave Cuthbert wrote:

Steve, I ran a SPICE model of the MFJ-1095 front end. What gain there is
resides there. The next three stages have unity gain. The input noise is:

1.8 MHz, 50 nV/Hz^0.5

7.0 MHz, 26 nV/Hz^0.5

14 MHz, 19 nV/Hz^0.5

28 MHz, 13 nV/Hz^0.5

Depending on the input stage gain (I'm modeling 1 to 2 depending on the
transformer) the three following stages can up the noise by 4-5 dB.

At 7 MHz the 26 nV/Hz^0.5 is 580 nV in a 500 Hz bandwidth, or -112 dBm.
This is 2.5 S-units. *What receiver are you using, what band and what is
the bandwidth? *

  Dave KH6AQ

On Sat, Mar 14, 2020 at 6:40 AM  wrote:


This discussion of Hi Z amplifiers has been quite interesting. Excellent
information from W1FV and K7TJR.

I have an RX amp question, related but slightly off-topic.

I have an MFJ-1025/1026 noise canceler. I like to use it on the higher HF
bands
to cancel power line QRN. The noise is typically S3-S4, but I want it down
to S0
to hear the bottom layer of stations. My sense antenna works fine, and the
QRN
is canceled. However, the MFJ-1025 amplifier noise is quite significant,
often
negating the QRN cancellation. The MFJ amplifiers are J310's. Any
recommendations for something quieter ?

73,
Steve, N2IC

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Re: Topband: Slightly OT - amplifier noise

[Dave Cuthbert]

Steve, I ran a SPICE model of the MFJ-1095 front end. What gain there is
resides there. The next three stages have unity gain. The input noise is:

1.8 MHz, 50 nV/Hz^0.5

7.0 MHz, 26 nV/Hz^0.5

14 MHz, 19 nV/Hz^0.5

28 MHz, 13 nV/Hz^0.5

Depending on the input stage gain (I'm modeling 1 to 2 depending on the
transformer) the three following stages can up the noise by 4-5 dB.

At 7 MHz the 26 nV/Hz^0.5 is 580 nV in a 500 Hz bandwidth, or -112 dBm.
This is 2.5 S-units. *What receiver are you using, what band and what is
the bandwidth? *

 Dave KH6AQ

On Sat, Mar 14, 2020 at 6:40 AM  wrote:

> This discussion of Hi Z amplifiers has been quite interesting. Excellent
> information from W1FV and K7TJR.
>
> I have an RX amp question, related but slightly off-topic.
>
> I have an MFJ-1025/1026 noise canceler. I like to use it on the higher HF
> bands
> to cancel power line QRN. The noise is typically S3-S4, but I want it down
> to S0
> to hear the bottom layer of stations. My sense antenna works fine, and the
> QRN
> is canceled. However, the MFJ-1025 amplifier noise is quite significant,
> often
> negating the QRN cancellation. The MFJ amplifiers are J310's. Any
> recommendations for something quieter ?
>
> 73,
> Steve, N2IC
>
> _
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>
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Re: Topband: Slightly OT - amplifier noise

[Jim Brown]

The DXE NCC-1 and NCC-2 are well equipped to deal with this. I haven't 
measured noise, but I did carefully measure phase shift and gain for 
multiple settings. They're in http://k9yc.com/VE3DO.pdf


73, Jim K9YC

On 3/14/2020 11:54 AM, Michael Tope wrote:
Another pitfall that you have to be careful to avoid with the MFJ-1026 
is making sure the level of the QRN you are trying null that is coming 
out of the sense antenna isn't much lower in amplitude than what is 
coming out of the main TX antenna


_
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Re: Topband: Slightly OT - amplifier noise

[Michael Tope]

Hi Mike,

Yeah, when the off-air noise floor is a lot higher than the thermal 
noise floor from the JFET pre-amps, the imbalance I was alluding to 
wouldn't typically impact the overall noise floor since that is still 
limited by off-air noise. In Steve's particular case, aside from one 
S3-to-S4 source of QRN, it sounds like has an extremely quiet QTH. Under 
those circumstances (especially since we are talking about the higher HF 
bands), the thermal noise from the receiver can start to dominate over 
the off-air noise. That is when getting the off-air QRN levels balanced 
between the two channels (as measured going into the MFJ unit) can matter.


FWIW, I've had the same experience as you nulling out local QRN. In my 
case it is noise picked-up on my 160 meter transmit antenna that I null 
with the MFJ-1026 using a 20ft top-loaded vertical as a sense antenna 
(it's what's left of a 160M RX 4 square that got shredded by the wind 
after some varmints chewed through the guy ropes). I should be so lucky 
as to have a QTH so quiet that the hiss from those JFET preamps is the 
dominate source of noise (that's quiet!).


73, Mike W4EF...

On 3/14/2020 11:57 AM, Mike Waters wrote:

Steve,
I have an MFJ-1025, and I have never experienced your issues. I was going
to ask some of these questions myself.

I have had very good results indeed with mine for eliminating a single
source of RFI. Something at your end is not right.

Mike,
There have been cases where my 580' Beverage antennas have made a superb
sense antenna. I usually use the W7IUV preamp with the output somewhat
attenuated. Mostly, with the signal antenna being my 75m dipole (with
severe RFI) and a amplified Beverage being the sense antenna.

Every QTH and noise is different, of course. What works for someone else
might not work for you.

73, Mike
W0BTU

On Sat, Mar 14, 2020, 12:46 PM Michael Tope  wrote:


2) Is your sense antenna intrinsically inefficient like a beverage or
K9AY loop or is it something efficient like a tribander up reasonably high?
3) Is your sense antenna intrinsically efficient when you include the
feed line loss (I assume the feedline loss on your main TX antenna is
very low)?

73, Mike W4EF

On 3/14/2020 9:40 AM, n2ica...@gmail.com wrote:

I have an MFJ-1025/1026 noise canceler. I like to use it on the higher
HF bands to cancel power line QRN. The noise is typically S3-S4, but I
want it down to S0 to hear the bottom layer of stations. My sense
antenna works fine, and the QRN is canceled. However, the MFJ-1025
amplifier noise is quite significant, often negating the QRN
cancellation. The MFJ amplifiers are J310's. Any recommendations for
something quieter ?

73,
Steve, N2IC



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Re: Topband: Slightly OT - amplifier noise

[Mike Waters]

Exactly! This is very important to get a deep noise null.

Mike W0BTU

On Sat, Mar 14, 2020, 1:55 PM Michael Tope  wrote:

> Another pitfall that you have to be careful to avoid with the MFJ-1026
> is making sure the level of the QRN you are trying null that is coming
> out of the sense antenna isn't much lower in amplitude than what is
> coming out of the main TX antenna (I am talking about levels measured
> directly from each antenna without the MFJ1026 in the line). For
> example, if you are getting -100dBm of QRM from the main antenna and
> only -110dBm from the sense antenna, then you could have a problem. If
> it is the case that the QRN level from the sense antenna is lower, then
> you have to use extra gain from the preamp in the sense antenna path or
> you have to attenuate on the main antenna path to get the two QRN
> voltages matched so they'll cancel effectively. Either way, you'll
> degrade the thermal noise performance. In the former case the sense
> channel will sum-in excess thermal noise, and in the latter case the
> attenuation added in front of the J310 in the main channel will degrade
> its effective noise figure.
>
> 73, Mike W4EF.
>
> On 3/14/2020 10:46 AM, Michael Tope wrote:
> > Steve,
> >
> > Couple of questions to rule out gain distribution issues:
> >
> > 1) On the sense antenna input do you have the pre-amp turned on or off?
> > 2) Is your sense antenna intrinsically inefficient like a beverage or
> > K9AY loop or is it something efficient like a tribander up reasonably
> > high?
> > 3) Is your sense antenna intrinsically efficient when you include the
> > feed line loss (I assume the feedline loss on your main TX antenna is
> > very low)?
> >
> > 73, Mike W4EF
> >
> > On 3/14/2020 9:40 AM, n2ica...@gmail.com wrote:
> >> This discussion of Hi Z amplifiers has been quite interesting.
> >> Excellent information from W1FV and K7TJR.
> >>
> >> I have an RX amp question, related but slightly off-topic.
> >>
> >> I have an MFJ-1025/1026 noise canceler. I like to use it on the
> >> higher HF bands to cancel power line QRN. The noise is typically
> >> S3-S4, but I want it down to S0 to hear the bottom layer of stations.
> >> My sense antenna works fine, and the QRN is canceled. However, the
> >> MFJ-1025 amplifier noise is quite significant, often negating the QRN
> >> cancellation. The MFJ amplifiers are J310's. Any recommendations for
> >> something quieter ?
> >>
> >> 73,
> >> Steve, N2IC
> >>
> >> _
> >> Searchable Archives: http://www.contesting.com/_topband - Topband
> >> Reflector
> >
> > _
> > Searchable Archives: http://www.contesting.com/_topband - Topband
> > Reflector
>
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>
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Re: Topband: Slightly OT - amplifier noise

[Mike Waters]

Steve,
I have an MFJ-1025, and I have never experienced your issues. I was going
to ask some of these questions myself.

I have had very good results indeed with mine for eliminating a single
source of RFI. Something at your end is not right.

Mike,
There have been cases where my 580' Beverage antennas have made a superb
sense antenna. I usually use the W7IUV preamp with the output somewhat
attenuated. Mostly, with the signal antenna being my 75m dipole (with
severe RFI) and a amplified Beverage being the sense antenna.

Every QTH and noise is different, of course. What works for someone else
might not work for you.

73, Mike
W0BTU

On Sat, Mar 14, 2020, 12:46 PM Michael Tope  wrote:

> 2) Is your sense antenna intrinsically inefficient like a beverage or
> K9AY loop or is it something efficient like a tribander up reasonably high?
> 3) Is your sense antenna intrinsically efficient when you include the
> feed line loss (I assume the feedline loss on your main TX antenna is
> very low)?
>
> 73, Mike W4EF
>
> On 3/14/2020 9:40 AM, n2ica...@gmail.com wrote:
> >
> > I have an MFJ-1025/1026 noise canceler. I like to use it on the higher
> > HF bands to cancel power line QRN. The noise is typically S3-S4, but I
> > want it down to S0 to hear the bottom layer of stations. My sense
> > antenna works fine, and the QRN is canceled. However, the MFJ-1025
> > amplifier noise is quite significant, often negating the QRN
> > cancellation. The MFJ amplifiers are J310's. Any recommendations for
> > something quieter ?
> >
> > 73,
> > Steve, N2IC
>
>
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Re: Topband: Slightly OT - amplifier noise

[Michael Tope]

Another pitfall that you have to be careful to avoid with the MFJ-1026 
is making sure the level of the QRN you are trying null that is coming 
out of the sense antenna isn't much lower in amplitude than what is 
coming out of the main TX antenna (I am talking about levels measured 
directly from each antenna without the MFJ1026 in the line). For 
example, if you are getting -100dBm of QRM from the main antenna and 
only -110dBm from the sense antenna, then you could have a problem. If 
it is the case that the QRN level from the sense antenna is lower, then 
you have to use extra gain from the preamp in the sense antenna path or 
you have to attenuate on the main antenna path to get the two QRN 
voltages matched so they'll cancel effectively. Either way, you'll 
degrade the thermal noise performance. In the former case the sense 
channel will sum-in excess thermal noise, and in the latter case the 
attenuation added in front of the J310 in the main channel will degrade 
its effective noise figure.


73, Mike W4EF.

On 3/14/2020 10:46 AM, Michael Tope wrote:

Steve,

Couple of questions to rule out gain distribution issues:

1) On the sense antenna input do you have the pre-amp turned on or off?
2) Is your sense antenna intrinsically inefficient like a beverage or 
K9AY loop or is it something efficient like a tribander up reasonably 
high?
3) Is your sense antenna intrinsically efficient when you include the 
feed line loss (I assume the feedline loss on your main TX antenna is 
very low)?


73, Mike W4EF

On 3/14/2020 9:40 AM, n2ica...@gmail.com wrote:
This discussion of Hi Z amplifiers has been quite interesting. 
Excellent information from W1FV and K7TJR.


I have an RX amp question, related but slightly off-topic.

I have an MFJ-1025/1026 noise canceler. I like to use it on the 
higher HF bands to cancel power line QRN. The noise is typically 
S3-S4, but I want it down to S0 to hear the bottom layer of stations. 
My sense antenna works fine, and the QRN is canceled. However, the 
MFJ-1025 amplifier noise is quite significant, often negating the QRN 
cancellation. The MFJ amplifiers are J310's. Any recommendations for 
something quieter ?


73,
Steve, N2IC

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Re: Topband: Slightly OT - amplifier noise

[Richard (Rick) Karlquist]

On 3/14/2020 10:20 AM, GEORGE WALLNER wrote:

Steve,
Sorry, I did not directly answer you question. Look at the specs of the 
IF3602. (But also look at the price!)

George
AA7JV



JFET's have a channel resistance that has thermal
noise like any other resistor.  That sets the
noise voltage for the device.  It is trivial to
simply produce a larger JFET or alternately
parallel a bunch of small ones, and you can
get as low a noise voltage as you want.  JFET's
also inherently have very low noise current.

The catch is that scaling up devices also scales
up capacitance.  No vendor AFAIK has made any
breakthru in terms of reducing capacitance vs IDSS.
That is the true figure of merit.  Without a
detailed analysis of the MFJ circuit, it is
hard to know if it could tolerate more capacitance.
Also, there may be other noise sources in the
MFJ as well.

Rick N6RK
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Re: Topband: Slightly OT - amplifier noise

[John Kaufmann via Topband]

Steve,

An alternative is to do the cancellation with all passive circuitry.  You
can find some designs on the Web but you'll have to build them yourself. An
example (one that I built) is this one from WA1ION:
https://www.pa4tim.nl/wp-content/uploads/2011/02/passive_bb_phasing.pdf.
The drawback to the passive designs is the insertion loss.  The WA1ION
design works quite well but I've measured its insertion loss as about 12 dB.
That may not be acceptable in many situations, particularly on the higher HF
bands.

73, John W1FV  

-Original Message-
From: Topband
[mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On Behalf
Of n2ica...@gmail.com
Sent: Saturday, March 14, 2020 12:41 PM
To: Topband
Subject: Topband: Slightly OT - amplifier noise

This discussion of Hi Z amplifiers has been quite interesting. Excellent 
information from W1FV and K7TJR.

I have an RX amp question, related but slightly off-topic.

I have an MFJ-1025/1026 noise canceler. I like to use it on the higher HF
bands 
to cancel power line QRN. The noise is typically S3-S4, but I want it down
to S0 
to hear the bottom layer of stations. My sense antenna works fine, and the
QRN 
is canceled. However, the MFJ-1025 amplifier noise is quite significant,
often 
negating the QRN cancellation. The MFJ amplifiers are J310's. Any 
recommendations for something quieter ?

73,
Steve, N2IC

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Re: Topband: Slightly OT - amplifier noise

[Michael Tope]

Steve,

Couple of questions to rule out gain distribution issues:

1) On the sense antenna input do you have the pre-amp turned on or off?
2) Is your sense antenna intrinsically inefficient like a beverage or 
K9AY loop or is it something efficient like a tribander up reasonably high?
3) Is your sense antenna intrinsically efficient when you include the 
feed line loss (I assume the feedline loss on your main TX antenna is 
very low)?


73, Mike W4EF

On 3/14/2020 9:40 AM, n2ica...@gmail.com wrote:
This discussion of Hi Z amplifiers has been quite interesting. 
Excellent information from W1FV and K7TJR.


I have an RX amp question, related but slightly off-topic.

I have an MFJ-1025/1026 noise canceler. I like to use it on the higher 
HF bands to cancel power line QRN. The noise is typically S3-S4, but I 
want it down to S0 to hear the bottom layer of stations. My sense 
antenna works fine, and the QRN is canceled. However, the MFJ-1025 
amplifier noise is quite significant, often negating the QRN 
cancellation. The MFJ amplifiers are J310's. Any recommendations for 
something quieter ?


73,
Steve, N2IC

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Reflector


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Re: Topband: Slightly OT - amplifier noise

[GEORGE WALLNER]

Steve,
Sorry, I did not directly answer you question. Look at the specs of the 
IF3602. (But also look at the price!)

George
AA7JV

On Sat, 14 Mar 2020 10:40:30 -0600
 n2ica...@gmail.com wrote:

This discussion of Hi Z amplifiers has been quite interesting. Excellent 
information from W1FV and K7TJR.

I have an RX amp question, related but slightly off-topic.

I have an MFJ-1025/1026 noise canceler. I like to use it on the higher HF bands 
to cancel power line QRN. The noise is typically S3-S4, but I want it down to 
S0 to hear the bottom layer of stations. My sense antenna works fine, and the 
QRN is canceled. However, the MFJ-1025 amplifier noise is quite significant, 
often negating the QRN cancellation. The MFJ amplifiers are J310's. Any 
recommendations for something quieter ?

73,
Steve, N2IC

_
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Re: Topband: Slightly OT - amplifier noise

[GEORGE WALLNER]

Steve,
The J310 is normally a pretty low noise device.
Perhaps you should look at filtering the power supply and any control and 
feed cables.

GL and 73,
George,
AA7JV


On Sat, 14 Mar 2020 10:40:30 -0600
 n2ica...@gmail.com wrote:

This discussion of Hi Z amplifiers has been quite interesting. Excellent 
information from W1FV and K7TJR.

I have an RX amp question, related but slightly off-topic.

I have an MFJ-1025/1026 noise canceler. I like to use it on the higher HF bands 
to cancel power line QRN. The noise is typically S3-S4, but I want it down to 
S0 to hear the bottom layer of stations. My sense antenna works fine, and the 
QRN is canceled. However, the MFJ-1025 amplifier noise is quite significant, 
often negating the QRN cancellation. The MFJ amplifiers are J310's. Any 
recommendations for something quieter ?

73,
Steve, N2IC

_
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Re: Topband: Slightly OT - amplifier noise

[Dave Cuthbert]

The J310 is as quiet as they come. It has a 100 MHz noise figure of (only)
1.5 dB.

   73 and aloha, Dave KH6AQ

On Sat, Mar 14, 2020 at 6:40 AM  wrote:

> This discussion of Hi Z amplifiers has been quite interesting. Excellent
> information from W1FV and K7TJR.
>
> I have an RX amp question, related but slightly off-topic.
>
> I have an MFJ-1025/1026 noise canceler. I like to use it on the higher HF
> bands
> to cancel power line QRN. The noise is typically S3-S4, but I want it down
> to S0
> to hear the bottom layer of stations. My sense antenna works fine, and the
> QRN
> is canceled. However, the MFJ-1025 amplifier noise is quite significant,
> often
> negating the QRN cancellation. The MFJ amplifiers are J310's. Any
> recommendations for something quieter ?
>
> 73,
> Steve, N2IC
>
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> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>
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