Re: Topband: Hi Gain Preamps, Noise Figure Comparison (KD9SV 994 x5, W1FB, W7IUV preamps)

2016-11-08 Thread Bob K6UJ 

Don,

Thanks for sharing your research on the preamps.  Very informative.
Your study is very timely for me.
I have ordered DX Engineerings new phasing box, NCC-2.
Optional plug in preamps are available for the unit.  I am holding off
on ordering a preamp until I compare specs with other external preamps.
The KD9SV unit looks pretty good !
Now to find out how it compares.

Bob
K6UJ



On 11/8/16 1:54 PM, Don Kirk wrote:

Gary (KD9SV) kindly loaned me one of his 994 x5 preamps (sometimes called
KD9SV VLN (very low noise) preamp) so I could compare its Noise Figure
against one of my W1FB preamps as well as 2 of my W7IUV preamps in series
on 160 meters.

Here is a link to a youtube video I created that demonstrates the
differences in Noise Figure between the above mentioned preamps.
http://www.youtube.com/watch?v=JpIiF1Hfovw

The KD9SV 994 x5 preamp did in fact come out on top (best Noise Figure) and
it's a commercially available preamp, whereas my W1FB and W7IUV preamps are
home built.  Nevertheless in my current application (pennants that are
51.6% the size of full size pennants) the W1FB and W7IUV preamp Noise
Figures are adequate and I didn't notice improvement in my signal to noise
ratio on 160 meters when using the KD9SV preamp.  The lower Noise Figure of
the KD9SV would allow me to use even smaller pennant receive antennas that
would have more negative gain without harming my signal to noise ratio.

I ran into a couple of interesting issues when working on this project.
The biggest surprise was that the input impedance of my old HF rig (Kenwood
TS-180s) was no where near 50 ohms on 160 meters (it actually measured 189
ohms).  I added a transformer to the input of the Kenwood TS-180s to bring
it closer to 50 ohms for my testing.

Also as previously reported by Hardy (N7RT) a long time ago, the W1FB
output transformer turns ratio is incorrect for a 50 ohm match, and I
measured the output impedance of the W1FB preamp at 429 ohms.  I
subsequently added a transformer to the output to bring it closer to 50
ohms for my testing.

*Noise Figure Comparison (average of two different measurement methods)*
W1FB preamp: Noise Figure 3.3 dB higher than KD9SV 994 x5 preamp
Two W7IUV preamps in series: Noise Figure 1.1 dB higher than KD9SV 994 x5
preamp

Note 1: my W1FB preamp is not stock, as I made modifications to protect the
MC1350 IC from damage when transmitting.
Note 2: The KD9SV 994 x5 preamp was set at its maximum gain (41 dB) for all
of my tests.

*Summary*
While I suspect (through my measurements) that the KD9SV preamp absolute
Noise Figure value is not the very low 0.7 dB value listed on a commercial
website, it's indeed a very nice adjustable high gain preamp offering a
maximum gain of 41 dB and it has the best (lowest) Noise Figure when
compared with my other two types of preamps.  I highly recommend the KD9SV
994 x5 preamp if you're in need of a high gain preamp on 160 meters.

73,
Don Kirk (wd8dsb)
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Re: Topband: Hi Gain Preamps, Noise Figure Comparison (KD9SV 994 x5, W1FB, W7IUV preamps)

2016-11-08 Thread Don Kirk 
Hi JC,

I did not publish any absolute Noise Figure values, my measurements that I
published are all just differences in Noise Figure.

It actually is much easier to measure the difference in Noise Figure
between preamps that have such high gain (approximately 40dB in this case)
since the noise floor generated by a 50 ohm resistor at room temperature is
easily measurable (at least indirectly) after 40 dB of gain (It's -106.89
dBm for a 40 dB preamp using a bandwidth of 500 hertz if the preamp adds no
additional noise).  Even if you can't accurately measure -106.89 dBm level
signals, you just need to be able to be repeatable in your measurements
between preamps (accuracy and repeatability are not the same thing), and
your system must be able to detect differences in output signal from the
preamp in units of dB (easy to do with an SDR receiver at these levels
using attenuators to verify changes in dB on the SDR display).  In my case
all of my measurements were made with my Kenwood TS-180s operating on 160
meters, and then making measurements via the wideband IF output port of the
Kenwood TS-180s that's connected to an SDR receiver (the HDSDR software
also allowed me to do long term averaging, and it even allows you to
display power spectrum density).

My second method of measurement used the S meter on my TS-180s, but just as
an indicator (actually digitized the voltage supplied to the S meter).  I
recorded the signal strength on the S meter that the preamp generated when
the preamp input was terminated with the 50 ohm resistor, then I went back
and adjusted my signal generator connected directly to my TS-180s via
attenuators until it provided the same S meter reading.  Using the signal
generator and precision attenuators I was able to calculate the voltage
(and therefore power) into the TS-180s that the S meter recorded when
driven by the preamp.  I used this technique to compare Noise Figure
between preamps, and I made numerous measurements over a 6 day period and
then averaged the data to reduce my variation using this method.

I did in fact test the use of #31 mix cores (10 to 14 turns) on various
lines (power supply lines, 3 foot short feedline between preamp and
receiver input, etc. and saw no difference in signal levels.  I even
eliminated the Kenwood power supply, and fed the TS-180s with a lab grade
linear power supply to eliminate slight changes in supply voltage over time.

P.S. the Kenwood TS-180s is one of the better radios made in regards to
noise floor (measured -139 dBm by Sherwood).

It would certainly be much easier to make these measurements using a
spectrum analyzer, and I probably will acquire one of the lower cost Rigol
spectrum analyzers in the near future.  In the meantime I would love to
have someone independently make measurements comparing these amplifiers
that either supports or disproves my measured values.

73,
Don (wd8dsb)


On Tue, Nov 8, 2016 at 7:24 PM, JC  wrote:

> Hi Don
>
> Measuring noise figure below 1 db is a very complicated work.
>
> First you need to remove all common mode noise, your noise floor should be
> better than  -135 dBm at least with a 40 db preamp connected to the radio
> input and a 50 ohms load.
>
> You need chokes everywhere and most important shield on 12V, RF in and RF
> out. Check the AM band you hear carrier coming in , noise is also coming
> in.
>
>  Second the NF is very different on 1.8 MHz , measurement near 10 Mhz, does
> not tell you the right NF on low bands.
>
> In order to have Noise Figure Uncertainty near .2db it is necessary a good
> quality lab equipment, calibrated and two hours per measurement for each NF
> reading. This assuming the temperature does no change during the test.
>
>
> Your Noise Figure Uncertainty based on your video could be 5db or more.
>
>
> 73's
> JC
>
> N4IS
>
>
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Re: Topband: Hi Gain Preamps, Noise Figure Comparison (KD9SV 994 x5, W1FB, W7IUV preamps)

2016-11-08 Thread JC 
Hi Don

Measuring noise figure below 1 db is a very complicated work. 

First you need to remove all common mode noise, your noise floor should be
better than  -135 dBm at least with a 40 db preamp connected to the radio
input and a 50 ohms load.

You need chokes everywhere and most important shield on 12V, RF in and RF
out. Check the AM band you hear carrier coming in , noise is also coming in.

 Second the NF is very different on 1.8 MHz , measurement near 10 Mhz, does
not tell you the right NF on low bands.

In order to have Noise Figure Uncertainty near .2db it is necessary a good
quality lab equipment, calibrated and two hours per measurement for each NF
reading. This assuming the temperature does no change during the test.


Your Noise Figure Uncertainty based on your video could be 5db or more.


73's
JC

N4IS

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Topband: Hi Gain Preamps, Noise Figure Comparison (KD9SV 994 x5, W1FB, W7IUV preamps)

2016-11-08 Thread Don Kirk 
Gary (KD9SV) kindly loaned me one of his 994 x5 preamps (sometimes called
KD9SV VLN (very low noise) preamp) so I could compare its Noise Figure
against one of my W1FB preamps as well as 2 of my W7IUV preamps in series
on 160 meters.

Here is a link to a youtube video I created that demonstrates the
differences in Noise Figure between the above mentioned preamps.
http://www.youtube.com/watch?v=JpIiF1Hfovw

The KD9SV 994 x5 preamp did in fact come out on top (best Noise Figure) and
it's a commercially available preamp, whereas my W1FB and W7IUV preamps are
home built.  Nevertheless in my current application (pennants that are
51.6% the size of full size pennants) the W1FB and W7IUV preamp Noise
Figures are adequate and I didn't notice improvement in my signal to noise
ratio on 160 meters when using the KD9SV preamp.  The lower Noise Figure of
the KD9SV would allow me to use even smaller pennant receive antennas that
would have more negative gain without harming my signal to noise ratio.

I ran into a couple of interesting issues when working on this project.
The biggest surprise was that the input impedance of my old HF rig (Kenwood
TS-180s) was no where near 50 ohms on 160 meters (it actually measured 189
ohms).  I added a transformer to the input of the Kenwood TS-180s to bring
it closer to 50 ohms for my testing.

Also as previously reported by Hardy (N7RT) a long time ago, the W1FB
output transformer turns ratio is incorrect for a 50 ohm match, and I
measured the output impedance of the W1FB preamp at 429 ohms.  I
subsequently added a transformer to the output to bring it closer to 50
ohms for my testing.

*Noise Figure Comparison (average of two different measurement methods)*
W1FB preamp: Noise Figure 3.3 dB higher than KD9SV 994 x5 preamp
Two W7IUV preamps in series: Noise Figure 1.1 dB higher than KD9SV 994 x5
preamp

Note 1: my W1FB preamp is not stock, as I made modifications to protect the
MC1350 IC from damage when transmitting.
Note 2: The KD9SV 994 x5 preamp was set at its maximum gain (41 dB) for all
of my tests.

*Summary*
While I suspect (through my measurements) that the KD9SV preamp absolute
Noise Figure value is not the very low 0.7 dB value listed on a commercial
website, it's indeed a very nice adjustable high gain preamp offering a
maximum gain of 41 dB and it has the best (lowest) Noise Figure when
compared with my other two types of preamps.  I highly recommend the KD9SV
994 x5 preamp if you're in need of a high gain preamp on 160 meters.

73,
Don Kirk (wd8dsb)
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