Noise Floor - Sherwood Engineering

Noise Floor - Sherwood Engineering
Transceiver Performance
What’s new in the last year?
Rob Sherwood
NCØ B
Lots of options for your dollars.
Sherwood Engineering
•
What is important in a contest environment?
•
Good Dynamic Range to hear weak signals in the
presence of near-by strong signals.
•
You need a better receiver for CW than for SSB.
•
Be a good neighbor: i.e. Have a clean signal.
•
Transmitters continue to be a mixed bag.
What Parameter is Most Important for
a CW Contester?
•
Close-in Dynamic Range (DR3)
•
(We have to know the noise floor to
calculate Dynamic Range)
What is Noise Floor?
Sensitivity is a familiar number, normally applies to SSB.
Sensitivity = 10 dB Signal + Noise / Noise (10 dB S+N/N)
Noise Floor = 3 dB Signal + Noise / Noise (3 dB S+N/N)
Noise floor can be measured at any filter bandwidth, CW or
SSB, for example, and is bandwidth dependent.
League normally only publishes noise floor for a CW
bandwidth, typically 500 Hz CW filter.
Noise Floor – Rarely an Issue on HF

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

On 20 meters and below, atmospheric, galactic and
man-made noise predominates.
On 15 meters, in a quiet rural location, the receiver is
still rarely the limit. Example:
NC0B, 5 element yagi at 70 feet, 270 feet of 7/8th
inch hardline, antenna pointed in the quietest
direction (30 degrees) at 4 PM on 2/28/2010.
Receiver sensitivity, no preamp, 2.4 kHz = 0.5 uV
Receiver sensitivity, w/ preamp, 2.4 kHz = 0.2 uV
Receiver noise floor, w/ preamp, 500 Hz = -135 dBm
LJ-155CA yagi in the previous example
A simple test with only a analog meter
 Most
hams don’t own a calibrated signal
generator.
 How do you evaluate your receiver?
 Measure the noise gain when you connect
your antenna.
 All you need is an analog meter with a dB
scale, hooked up to your speaker.
Measure the noise gain
 Disconnect
your antenna and set the volume
so your dB meter reads -10 dB.
 (Put a dummy load on the rig, but it will likely
make no difference.)
 Connect the antenna and see how many dB
the noise goes up when tuned to a dead spot
on the band.
 Do this with Preamp OFF and ON
What did I measure on 15 meters ?
 With
preamp OFF, noise gain = 3.0 dB
 With preamp ON, noise gain = 8.3 dB
 (This was in the quietest direction!)
 With the preamp ON, now rotate your yagi
360 degrees and note the difference in noise.
 In the direction there is skip, the noise will be
higher.
 Can be a 10 dB difference in band noise vs.
direction.
15 & 10 meters not that different
Rig = IC-756 Pro III
10 meter antenna = Hy-gain 105CA @ 65 feet
15 meter antenna = Hy-gain 155CA @ 70 feet
Preamp
15 M
10 M
None
4 dB
3 dB
Preamp 1
11.5 dB
9.5 dB
Preamp 2
13.0 dB
11.0 dB
More Variables – Plan ahead if you can
 At
my QTH there are two towers near the
house and four 200 to 350 feet away. My
noise level on 20 – 10 meters is vastly worse
for the close-in towers, unless I turn off
electronic devices.
 TVs (CRT or plasma), UPS & family-room
computer, broadband router (makes birdies),
wireless Internet dish, wall warts with
switching power supplies, hand touch lamp !
Tower Distance vs. local RFI (noise)
Numbers with Preamp-1 ON
Noise Floor Quite Consistent in Top 10
 FTdx-5000D
-135 dBm
 Elecraft K3
-138 dBm
 Perseus -125 dBm (No preamp)
 Flex 5000
-135 dBm
 Orion II -133 dBm
 Orion I
-135 dBm
 T-T Eagle
-132 dBm
 Flex 3000
-139 dBm
 TS-590S -137 dBm
 Icom R9500
-130 dBm
 Drake R-4C
-138 dBm (For comparison)
What is Dynamic Range?
The range in dB of very strong signals to very weak signals
that the receiver can handle At The Same Time
What is Close-in Dynamic Range vs
Wide-Spaced Dynamic Range?
Why is Close-in Dynamic so important for CW ops?
Why is it less important for SSB operators?
Third Order IMD to
Measure Dynamic Range
Signal
Signal
2 kHz spacing
IMD
2 kHz spacing
IMD
2 kHz spacing
Wide & Close Dynamic Range
20 kHz Spacing
IMD 20 kHz Away
15 kHz Wide
First IF Filter at 70.455 MHz
2 kHz Spacing
IMD 2 kHz Away
15 kHz Wide
First IF Filter at 70.455 MHz
Highest performance with a bandwidth appropriate filter
right up front after the first mixer.
Mixer
SSB BW
Filter
Amplifier
Mixer
DSP
Filtering
CW BW
Filter
This keeps the undesired strong signals from progressing
down stream to the next stages.
What has changed in last 8 years?
 Ten-Tec
started the change in 2003 with the
Orion, the first radio to drop “up-conversion”
and go back to a low first IF.
 Elecraft followed, and now Yaesu and
Kenwood in 2010.
 Only Icom has of yet not offered a “downconversion” radio
 If the TS-590S is a big seller, will Kenwood
follow on with a larger and more expensive
model?
When are 2 Out of Pass
Band Signals a Problem?
• If you know the close-in dynamic range of a radio, at what
signal level will IMD start to be a problem?
• S Meter standard is S9 = 50 V, which is –73 dBm
• Assume a typical radio:

500 Hz CW filter

Noise Floor of -128 dBm

Preamp OFF
Dynamic Range
Signal Level Causing IMD = Noise Floor
55 dB
S9
FT-757 (56 dB)
60 dB
S9 + 5 dB FT-2000 (61 dB)
65 dB
S9 + 10 dB IC-7000 (63 dB)
70 dB Typical Up-conversion
S9 + 15 dB 1000 MP / Mk V Field (68 / 69 dB)
75 dB
S9 + 20 dB 756 Pro II / III (75 dB)
80 dB
S9 + 25 dB Omni-VII / IC-7800 (80 dB)
85 dB
S9 + 30 dB TS-590S (88 dB)
90 dB
S9 + 35 dB Eagle & Flex 3K (90 dB)
95 dB
S9 + 40 dB Orion II & Flex 5000A (95 dB)
100 dB
S9 + 45 dB FTdx-5000, K3 (200 Hz roofing)
Close-in 2-kHz Test @ 500 Hz BW
Dynamic Range of Top 8 Transceivers
 FTdx-5000D
 Flex
5000
 Elecraft K3
 Orion II
 Orion I
 TT Eagle
 Flex 3000
 TS-590S
 TS-590S
101 dB
96 dB (Flex users raise hand)
95 dB (with 500 Hz filter)
95 dB
93 dB
90 dB
90 dB
88 dB (Low Freq 1st IF mode)
76 dB (30, 17, 12, 10 & 6 M)
How did the new rigs perform on CW?
I
used the FTdx-5000, TS-590S and Eagle in
the 160 m. ARRL, Stew Perry & CQ contests.
 Switched between the Kenwood and the TenTec during the CQ contest.
 Overload was never an issue.
 All could crank down the DSP filter to 100 Hz
or narrower.
 Ran most of the contest at 200 Hz BW
 Definitely needed 50 to 100 Hz BW
Narrow DSP Filters Come Through
 In
all three contests working CE1/K7CA
required the narrowest bandwidths to copy
through the pile-up, since he was not working
split.
 Thank goodness the DXpeditions work split,
so you can hear when the DX comes back to
you.
 You can imagine what it is like at the DX
location: total pandemonium for days!
The DR3 “window” is not fixed
The dynamic range of a radio is the same with an
attenuator ON or OFF.
If on a noisy band, attenuate the noise and all signals to
make better use of the dynamic range, and reduce the
chance of overload.
If band noise goes from S6 to S2 by turning on the
attenuator, you have lost nothing, yet your radio is being
stressed much less.
Let’s now look at the transmitters
I
am now testing transmitters with white noise
feeding the microphone, in addition to a twotone test.
 The effect of IMD products (splatter) are
more obvious with noise.
 Think of it as a 1000 tone test, more
approximating real voice.
White Noise Mk V Class A vs. K3 Class B @ 75 Watts
-60 dB
6 kHz
-60 dB
1.5 kHz
Courtesy W6XX
What shipped since Dayton 2010?
Yaesu
FTdx-5000D
Kenwood TS-590S
Ten-Tec Eagle
Ten-Tec Eagle Class B White Noise
60 dB down 7 kHz away
Kenwood 590S Class B White Noise
60 dB down 5 kHz away
7600 about 10 dB worse than the Pro III
IC-7600 on top, 756 Pro III on bottom
8 dB Offset
18 dB difference
at 6 kHz
FTdx-5000D Class A – Two Levels ALC
ALC Half Scale
60 dB down 2 kHz away
No ALC
What’s wrong with the FTdx-5000D?
 Decades
ago Collins clearly stated that an
ALC circuit should have a SLOW time
constant (decay). ALC should just be a slow
leveling circuit. Speech processing should
be done way before the PA and the ALC.
 This issue can be fixed, either in hardware or
in firmware, but I don’t know which it is.
Ham breaks into my 20 meter QSO
 When
some breaks in to comment on your
signal, what is your first thought?
 “I must be splattering”
 With the 5000D in Class A, and NO ALC, the
ham broke in to say I had the cleanest signal
he had ever seen on the air with his K3 and
his P3 bandscope.
What Could Contests Be Like?
 What
would CQ WW or ARRL DX be like if
everyone had a signal this clean?
 Yet some hams don’t want a clean signal.
 They want “elbow room”.
 This goes back to Contest Ethics from this
morning!
Back to CW signals
We have seen how width of an SSB signal & its
IMD products affects how close you can operate
to another station.
How does CW compare?
How close can we work to a strong adjacent CW
signal?
What is the Bandwidth of CW Signal?
On channel signal = S9 + 40 dB (-33 dBm)
Receiver = K3, 400 Hz 8-pole roofing + 400 Hz DSP Filter
Transmitter = Omni-VII with adjustable rise time
Undesired signal 700 Hz away, continuous “dits” at 30 wpm
Rise time of Omni-VII
Signal
3 msec
4 msec
5 msec
6 msec
7 msec
8 msec
9 msec
10 msec
Strength of CW sidebands
S9 + 40
-33 dBm
S7
-83 dBm
S6
-88 dBm
S6
-88 dBm
S5
-93 dBm
S4
-99 dBm
S4
-99 dBm
S4
-99 dBm
S3
-105 dBm
Ref
-50 dB
22 dB !
-72 dB
Spectrum of CW Signal on HP 3585A Analyzer
Rise Time 10 msec, “dits” at 30 WPM,
Bandwidth -70 dB = +/- 450 Hz = 900 Hz
Spectrum of CW Signal on HP 3585A Analyzer
Rise Time 3 msec, “dits” at 30 WPM,
Bandwidth -70 dB = +/- 750 Hz = 1500 Hz
Spectrum of CW Signal on HP 3585A Analyzer
Comparison of 3 msec vs 10 msec rise time
20 dB
difference
Leading edge of “dit” 3 & 10 msec
Just the Facts
On SSB you want DR3 = 70 dB, or more.
On CW you want DR3 = 80 dB, or more.
This is most economically accomplished with low IF
(5 to 9 MHz) selectable crystal roofing filters.
It is much more difficult to deliver 80 dB or higher
DR3 with the more common Up-Conversion design.
Transmitted bandwidth of the interfering signal is
often the limit, not the receiver.
What dynamic range is possible and needed for CW?
80 dB or better @ 2 kHz with a 500 Hz bandwidth.
2001 Ten-Tec Omni-VI+:
80 dB
2003 Icom IC-7800:
80 dB
2003 Ten-Tec Orion I:
93 dB
2005 Ten-Tec Orion II:
95 dB
2007 Flex 5000A:
96 dB
2007 Ten-Tec Omni-VII:
80 dB
2008 Elecraft K3:
95 dB
2010 Kenwood TS-590S:
88 dB
2010 Ten-Tec Eagle:
90 dB
2010 FTdx-5000:
101 dB
Other radios for comparison, 2 kHz dynamic range data
Elecraft K2:
80 dB
Collins R-390A:
79 dB
Kenwood TS-850S:
77 dB
Icom Pro II / Pro III
75 dB
Collins 75S-3B/C:
72 dB
Kenwood TS-870S:
69 dB
Yaesu FT-2000:
63 dB This is shockingly bad
Icom IC-7000:
63 dB
Yaesu FT-One:
63 dB
Yaesu FT-101E:
59 dB
Drake R-4C Stock:
58 dB
Yaesu FT-757:
56 dB
Yaesu VR-5000:
49 dB Worst radio I have ever tested !
Bogus ARRL Dynamic Range Numbers
 Many
modern transceivers are phase noise
limited, particularly close-in at 2 kHz. The
League wanted be able to measure the IMD
buried in the phase noise, and came up with
a new method a few years ago using a
spectrum analyzer with a 3-Hz filter.
IC-7600 with 3-Hz Spectrum Analyzer
Reference tone
-130 dBm
IMD @ -130 dBm
500 Hz DSP
Filter Passband
Phase noise
limited
dynamic
range is 78
dB at 2 kHz.
Measured
with a 3-Hz
filter on the
analyzer, the
dynamic
range is 87
dB at 2 kHz!
What the New ARRL DR3 Method Means
 Old
method, IMD or noise increased 3 dB.
 IMD tone at noise floor =
 This was DR3, either IMD or noise limited.
 With the new method, noise increased 10 dB,
and by ear you hear nothing but noise.
 How is this the same?
 Unless you work a contest using a 3-Hz CW
filter, the new League dynamic range
measurements are meaningless. If the radio
is phase noise limited.
IC-7800 ARRL Old vs. New Method
 4/18/2006
IC-7800 test data, old method
 2 kHz, Phase Noise Limited @ 80 dB
 1 kHz, Phase Noise Limited @ 67 dB
 2/6/2007
IC-7800 test data, new method
 2 kHz, dynamic range = 86 dB
 No measurement reported at 1 kHz.
Flex 3000 Old Method vs. 3 Hz Filter
 Flex
3000 with Old Method: DR3 = 90 and is
completely phase noise limited.
 Flex
3000 with 3 Hz Spectrum Analyzer
method measures a dynamic range between
95 and 99 dB, depending on the spacing.
 The
Orion II and the K3 perform better, but
now you cannot tell that by the QST
numbers.
Phase noise should not be ignored !
 The
problem is the League is now measuring
dynamic range in such a way to eliminate
phase noise from the equation. Phase noise
(reciprocal mixing in a QST review) gets but
a single line of data.

An Elecraft K3 at 99 dB is not the same as a
Flex 3000 at 99 dB, yet you would never
know that from a QST review.
Question: How good is good enough?
High Dynamic Range Receiver (DR3).
Minimum 70 dB for SSB & 80 dB for CW
If the “real” DR3 > 90 dB, your receiver is fine.
Differences of a few dB are NOT significant.
Sensitivity 15 meters and below, preamp ON: 0.2 uV
Noise floor 15 meters and below, preamp ON: -135 dBm
Receiver testing needs to approximate the real world.
Sherwood Engineering
http://www.sherwood-engineering.com
http://www.NC0B.com
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