Out, Damn Noise

1
Out, Damn Noise!

• (or Fighting Noise in a Mobile Environment)
• Presented by
• Jim, K0MHC/R
• froemke_at_attglobal.net, e-Mail
• http//www.clarc.org/rmg/k0mhc.html, web page
• AURORA/2000, April 29th, 2000

2
Preface

• The author and contributors have no interest in
  any of the companies or their products tested.
  Equipment owned by various hams was used.
• These tests were obtained under typical amateur
  radio operating conditions rather then formal
  laboratory bench testing. Your results may vary
  from those included in this report.
• Thanks to KE9IT for the loan of equipment.
• E-mailed comments, questions, suggestions and
  references would be appreciated.
• Have you fed a rover today?

3
Topics

• Introduction
• Rover considerations
• Receive signal-to-noise ratio
• Factors you have control over
• Mobile configurations
• The mobile (rover) noise environment
• External and internal noise sources
• Some Noise Solutions
• Rover recommendations
• Summary
• Work in progress
• References

4
Introduction to noise elimination

• Roving can be one of the most challenging and
  rewarding form of ham radio operations.
• Its worth while remembering that there are from
  4 to 8 spark gap transmitters under you hood and
  many more on the road near you!
• If you cant hear them, you cant work them!

5
Rover Considerations

• Strategy
• Propagation
• Locations
• Scheduling
• Operator skill
• Number of bands and grids activated
• Operating modes
• Transmit signal
• Receive interference
• Receive signal-to-noise ratio

6
Receive Signal-to-Noise Ratio(or You Cant Work
Them If You Cant Hear Them!)

• RF signal optimization
• Effective antenna gain (i.e., capture area)
• Effective reception angle
• Low feed line loss
• RF noise minimization
• Source (external or internal)
• Type
• Strength
• Direction (elevation and horizontal)
• Polarization
• Bandwidth

7
Receive Signal-to-Noise Ratio(or You Cant Work
Them If You Cant Hear Them!)

• The ability to copy a weak signal depends
  primarily on the signal-to-noise ratio (S/N).
• S/N can be expressed in a formula as
• S/N (dB) ERP PL ERS
• ERP Effective Radiated Power
• PL Path Loss
• ERS Effective Receiver Sensitivity

8
Receive Signal-to-Noise Ratio(or You Cant Work
Them If You Cant Hear Them!)

• ERP of the base station is the transmit power
  minus the coax loss plus the antenna gain (at the
  desired vertical take-off angle).
• For example 200W (23 dBW) through 100 LMR400UF
  (-1.7 dB) into a 2M5WL (17 dBi) yields and ERP
  of approximately 38.3 dBW on 2 meters.
• PL is greatly effected by band selected, current
  propagation conditions and the method of
  propagation.

9
Receive Signal-to-Noise Ratio(or You Cant Work
Them If You Cant Hear Them!)

• ERS of the mobile station includes the receive
  noise floor power level, effective receive
  antenna capture area and coax losses. It can be
  expressed as
• ERS(dBW) 10logk(Trx Tant)BW)dBW) RX
  (antenna gain, dBi)
• Trx Noise temperature of the receiver (or
  pre-amp)
• Tant Noise temperature of the receiving antenna
• BW Bandwidth
• RX Effective receive antenna capture area (gain
  dBi) at desired reception elevation

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Factors you have control over

• Trx, Receiver (pre-amp) noise temperature
• This is usually NOT a significant factor for
  terrestrial propagation modes due to the
  relatively high terrestrial noise signal levels.
  (This is a big deal for EME!)
• RX, Receive antenna gain
• The actual antenna receive gain at the desired
  reception angle and ground gain are influenced by
  the effective height above ground.
• Interaction with other resonate conductors
  located within its capture area can reduce the
  effective receive capture area.
• Coax losses would be subtracted from the antenna
  gain.
• Receive antenna directivity also reduces the
  noise signal strength from external, noise
  sources that are directional in the horizontal
  and elevation.

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Factors you have control over

• Signal Mode Bandwidth
• NBFM (/- 5000 Hz) reference
• SSB (2000 Hz) yields a 7 dB improvement
• CW (500 Hz) yields a 13 dB improvement
• PSK31 (31 Hz) yields a 25 dB improvement
• Note that these improvements are approximate
  and will very depending on your equipments
  performance and your brains ability to process
  signals (i.e, experience).
• Bandwidth improvement (dB) 10log(BWnbfm/BWmode
  )
• PSK31 is currently available on HF and low VHF
  (6 2).

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Mobile Configurations

• Ideal Configuration
• In the ideal case (figure 1) there are very few
  components and noise sources.
• Typical Configuration
• In the typical case (figure 2) there are many
  components and noise sources that would need to
  be considered.
• Test Configuration
• The test case (figure 3) was reduced to a minimum
  configuration for time and repeatability
  considerations.

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Figure 1. Ideal Configuration
Antenna
RF Signal
Speaker
AF Sound
DC Power
Microphone
Transceiver
14
Figure 2Typical Configuration
Noise
Noise
Receive Signal Elevations
Noise
Noise
Antennas
Relay
Noise
Noise
Switch
Noise
Noise
Amplifier
Noise
DC Power
AF Sound
15
Figure 3 Test Configurations
Receive Signal Elevations
Directional Noise Source
External
Antenna
Noise Sample Antenna
Amplifier
Internal
ANC-4
Filtered DC Power
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The mobile (rover) noise environment

• External noise sources
• Atmospheric
• Nearby Power Lines
• Ignition from other vehicles
• Internal noise sources
• Conducted noise in your DC power distribution
• Radiated noise in your ignition and charging
  systems
• Other automotive electrical components (e.g.,
  fuel pump, oil pressure sender, air conditioning
  fans, etc.)
• Amplifier cooling fans
• Power inverters (DC/AC, DC/DC and DC/AC)
• Logging computer
• GPS

17
Finding Noise Sources

• Snoop with an HT for radiated noise and
  transmit RF leakage.
• Set to AM mode (6 meters or aircraft band) while
  you probe for radiated noise sources. This works
  VERY good!
• Monitor the 0.7 meter, third harmonic signal
  strength from your VHF transmitter (using a
  shielded, dummy load) while probing for leaking
  connectors with your HT.
• Monitor the VHF bands using AM mode on your
  multi-mode, multi-band transceiver for both
  radiated and conducted noise sources (with and
  without a probe antenna).
• View an oscilloscope to check DC and AC
  distribution for conducted noise.

18
Some Noise Solutions

• RF- Amplifier (brick) Considerations
• RF- Directional Antennas
• RF- Antenna Noise Cancellers
• RF- Vehicle Electronics System Alternatives
• RF- Additional Automotive Grounding
• IF- Filters and DSPs
• AF- Noise Blankers
• AF- DSPs
• AC- Power Inverters
• DC- Voltage System

19
RF- Amplifier (brick) Considerations

• Your brick can pick up considerable noise and
  pass it along.
• Proximity to radiated nose from power inverters
• Conducted noise from the DC power distribution
• Radiated noise from amplifier cooling fans
• Good cooling is critical for survival of
  amplifiers!
• Lower amplifier temperatures increase power
  output, lowers drive level and decreases current
  drain.
• Both internal and external fans can be noise
  sources.
• RadioShack P/N 273-243B 3 brushless 12V fan
  works good.
• Panaflo 3K15DN 3 ½ brushless 12V fans are
  HORRIBLE!
• May need to ground the amplifier frame in some
  cases.
• Connect both a stiffing ¼ to ½ F and RF bypass
  capacitor 1000 uF AT THE AMPLIFIER DC TERMINALS.
• Low DC voltage can damage your amplifier and
  produce non linear signal output. They run much
  better with between 13.8 and 14.5 V.

20
RF- Directional Antennas

• The goal is to increase the received signal
  strength while minimizing the received noise
  strength.
• Vertical Plane- Reception on 6 and 2 meters is
  improved with a lower antenna reception angle
  because of the relatively high arrival angle for
  most atmospheric noise.
• The effective antenna height above ground is
  important.
• Stacking can also be helpful, with proper spacing
  but, it lowers the average antenna height.
• Ground gain picks up gt1 wave length above ground.
• Fixed roof versus telescoping mast antenna mount
  debate.
• Horizontal Plane- Reception on 6 and 2 meters is
  also improved with a narrower antenna beam width
  in order to aim away from directional noise
  sources. (Not all noise sources are directional.)
• Omni directional versus directional antenna
  debate
• Your roving strategy will influence your antenna
  types and height.

21
RF- Antenna Noise Cancellers

• The goal is to minimize the noise BEFORE it
  enters your rig.
• The principle is to use two, separate antenna
  sources and combine them 180 out of phase in
  order to null out the undesired signal source.
• The noise sampling antenna must be of the same
  polarity as the undesired signal source but, with
  less signal capture capability then the main
  antenna. May need a separate antenna per band.
• Pros
• Very effective at eliminating atmospheric white
  nose, power line, auto ignition and misc.
  automotive QRN up to 6 meters.
• Cons
• Not effective on atmospheric static crashes!
• Some units introduce up to 6 dB signal loss on
  receive.
• Needs to be re-tuned for each band.

22
RF- Antenna Noise Cancellers

• In theory, this technique will work well into the
  VHF frequency range. In practice, some commercial
  and home brew units work up to 6 meters and above
  with modifications.
• ANC-4 by JPS (now Timewave) up to 80 MHz
• MFJ-1026 by MFJ, www.mfjenterprises.com
• QRN Squasher by W1FB, CQ. 6/1996, pg. 24 CQ,
  7/1997, pg. 62
• 6 Mr Interference Reduction System by G3ZYY,
  www.uksmg.org/eliminate.ht
• Local RF Interference Canceller,
  www.radiosky.com/cancelit.htm
• Measurements of an ANC-4 showed a 12 dB
  improvement in S/N with ignition noise on 6
  meters. A pre-amp (within the power amplifier)
  ahead of the ANC-4 restored the 6 dB receive
  signal strength loss which could have affected
  the NB performance.

23
RF- Vehicle Electronics System Alternatives

• The goal is to eliminate the conducted and
  radiated noise.
• You can choose to noise proof your vehicle.
• Refer to the WA6PDPs excellent article in QNX.
• This allows you to operate in-motion or idling
  with a significant reduction in noise levels from
  YOUR vehicle.
• A tune-up with new resister plugs and ignition
  suppression wires can be very effective when
  combined with a fuel pump noise filter.
• Shielding your entire ignition system takes a
  significant investment in time and may have new
  vehicle warranty implications.
• You can choose to operate without your engine
  running.
• Battery(s) tend to quickly run down resulting in
  significant linear amplifier distortion. Dont
  forget the jumper cables!
• An auxiliary AC generator may be a good
  alternatives for you.

24
RF- Noise Suppression Techniques

• The goal is to suppress noise at their sources.
• Shield radiating noise sources. Distance and
  grounding help minimize the residual noise.
  Shielding cables (DC, AC and control) may also be
  necessary.
• RF cables need good shields and connectors to
  avoid picking up radiated noise. This is a major
  source of problems!
• Filter conductive noise at the source. Decoupling
  the DC distribution at each load is usually
  helpful.
• The best ground in your vehicle is the metal
  floorboard. Very SHORT and WIDE ground straps can
  be attached to seat bolts or additional bolts
  through the metal floorboard.
• Mount noise radiating devices directly to the
  metal floorboard with bolts where ever possible.
  Use star washers on all RF grounds to cut
  through painted surfaces and lower impedance.
• Connect each RF component via short, wide ground
  straps directly to the metal floorboard. Dont
  daisy chain them!

25
IF- Noise Blankers

• The goal is to reduce impulse noise without
  distorting strong signals.
• Input signal levels need to be adequate for the
  noise blanker to function correctly. This may
  require turning on the pre-amp in either the
  transceiver or brick (increased exposure to inter
  modulation).
• If a received signal level is too high, the noise
  blanker will distort the signals of strong
  stations. Try turning off your noise blanker
  before you give another station a splatter
  signal report.
• Adjusting your AGC can change the effectiveness
  of the noise blanker and reduce the effects of
  noise. Try fast and low AGC both with and without
  your noise blanker.
• Noise blankers are designed to be most effective
  on ignition type of pulse noise. They are not as
  effective on other types of noise.
• Measurements of an FT-847 and IC-706-IIG both
  resulted in satisfactory impulse noise reduction
  of from 2 to 4 S units and significant
  improvement in readability.

26
AF- DSPs

• The goals of the DSP are
• Reduce the bandwidth of the received signal
  (improved S/N).
• Filter out signals having the characteristic of
  noise without reducing the readability.
• Remove undesired beat notes within the IF pass
  band. (Dont use the notch filter in CW mode!)
• In theory a DSP would be most effective in the RF
  stage, next best in the IF stage and least
  effective in the AF stage. In practice,
  improvements can be obtained in most cases with
  an AF-DSP except when dealing with very strong
  signals.
• As with an IF Noise Blanker, the DSP needs
  adequate input signal level to function
  correctly. In most cases, DSPs are adjustable to
  trade off noise reduction for readability.
• IF filters are good investments ahead of an
  AF-DSP.
• Measurements of an AF-DSP in an FT-847 and
  IC-706-IIG both showed improvements in S/N and
  readability. The FT-847 was much easier to adjust
  and had more readable audio.

27
AC- Power Inverter

• This goal is to provide the necessary AC power
  without generating conductive or radiated RF
  noise.
• AC power required for laptop, antenna rotor, etc.
• DC to AC power inverters are a major source of
  radiated RF noise on 6 and 2 meters. Noise
  elimination requires grounding, filtering input
  output, EMI shielding and short, heavy cables.
• The RF- Antenna Noise Canceller did reduce this
  noise.
• The noise blankers were NOT very effective with
  inverter noise.
• Measurements were made of two, stock power
  inverters on 6 meters fed from the cigarette
  lighter powering a 100W light
• Radio Shack 22-132B yielded 6-12 B rise in noise
  level.
• Tripp Lite LW3AH yielded 6-10 dB rise in noise
  level.
• After noise elimination both had detectable noise
  levels.

28
DC- Voltage System

• The goals of the DC system are
• Provide stable DC power for long periods of time.
• Well regulated at gt 13.8 VDC with lt 100 mV RMS
  ripple
• Capable of supplying very high currents (in
  excess of 50-70 amp. peaks) within regulation.
• Distribution to multiple, high current
  components.
• No conducted RF noise component.
• Short circuit and over-voltage protection.
• Alternatives include the vehicle alternator,
  batteries with a voltage stabilizer and DC
  supplies fed from an auxiliary AC generator.
• The vehicle cigarette lighter plug is a very poor
  source of DC.
• Multiple batteries with a DC voltage stabilizer
  may be a good option for hybrid operation
  (in-motion and stopped).
• The number of batteries would depend on current
  and time.

29
DC- Voltage Stabilizer

• The goal of a voltage stabilizer is to sustain
  normal DC voltage level during high current peaks
  and while the batteries discharge.
• Batteries discharge quickly with heavy current
  drains. Multiple batteries (of the same type) can
  be connected in parallel.
• Amplifiers reduce power output and go into
  extreme non linear operation with low voltage
  (below approximately 11.5 VDC).
• Use of a DC to DC power inverter can stabilize
  the voltage level at 14 VDC (user adjustable)
  when run from a battery voltage varying from
  about 13.8 (while charging) to approx. 10 VDC.
• As with DC to AC power inverters, the DC to DC
  power inverter must be properly shielded,
  bypassed, input output grounded, cooled and use
  short, heavy cables for DC distribution.
• Measurements of a Jacobs model FR1500W Accuvolt
  unit set for 14 V at 2 amp showed considerable
  radiated noise on 6 2 mrs. Voltage drop under
  load measured at the TE Systems 0552G (375W)
  amplifier input was 0.1 V at 40 amp load and 0.6
  V at 60 amp which did NOT meet specifications. It
  stopped regulating at 10.9 V which DIDNT meet
  specs (returned for warranty repair).

30
Rover Recommendations

• RF-
• Consider directional receive antennas to increase
  desired signals and reject directional noise
  sources.
• Higher antennas will improve gain at the desired
  receive angles.
• A 0.7 wavelength high (13.5) full size loop for
  6 meter is a relatively good antenna for nulling
  directional noise and receiving signals. Pushing
  it up to 20 while stopped is easy and effective.
• Use good, low loss, well shielded coax
  transmission line.
• Its the plumbing, stupid! Snoop for lossy coax
  connectors.
• Consider an antenna noise canceller to improve 6
  meter reception. Can be modified for use on 2
  meters.
• Use good (short and wide) RF grounds to the
  vehicle chassis.
• Consider an ignition tune-up (plugs and wires)
  above 50K miles.
• Shield and bypass fans and motors.

31
Rover Recommendations

• IF-
• Go out and buy the best narrow band IF filter(s)
  that you can afford to improve the S/N (lower
  bandwidth) and reduce AGC overload from strong
  noise sources.
• A good noise blanker can help reduce impulse
  noise. Test a rig before you buy it.
• An IF- DSP may also be beneficial in improving
  the S/N and reducing overload from strong noise
  sources (not tested). These are not yet available
  in most mobile size rigs.
• AF-
• A good DSP can both reduce many noise types,
  notch out undesired beats and further improve the
  S/N with narrower bandwidth.
• Headphones can significantly reduce vehicle audio
  noise interference but, dont try to drive with
  them on.

32
Rover Recommendations

• DC-
• Filter all DC power used from the vehicle
  charging system.
• Shield, filter and ground any power inverter
  inputs AND outputs.
• The voltage stabilizer tested did NOT meet
  specifications.
• Eliminate ignition/alternator/fuel pump noise by
  operating from battery or AC generator power
  while stopped (engine off).
• Other-
• Select operating locations with low external
  noise sources as well as high, unobstructed lines
  of sight.
• Utilize low bandwidth modes (CW and PSK31) when
  possible.
• Keep safety in mind! (batteries can tip over
  and/or explode!).
• KISS!

33
Summary

• Noise elimination is a never ending endeavor.
  Its like peeling an onion. As soon as you
  minimize one type of noise, another is there to
  greet you.
• Noise elimination can have a big pay back
  especially in the lower VHF (6 2) meter (and
  HF) bands.
• Many of the noise elimination solutions also help
  to improve your rover transmission capability.
• Many of the lessons learned can also be applied
  to fixed, base VHF stations and most HF stations.
• PSK31 looks like a good weak signal DX mode for
  6, 2 and higher.
• Noise elimination is a labor intensive activity!
  Set aside a week for noise isolation and
  elimination before the next contest.

34
Work in Progress

• Retesting of a replacement Jacobs voltage
  stabilizer
• Testing of the YAESU FT-100 transceiver
• Testing of a transceiver with an IF-DSP
• Testing of stacked omni-directional loops on 6
  and 2 meters
• Additional directional versus omni-directional
  antenna tests
• Noise polarization and reception angle
  measurements
• Modifications to an ANC-4 for 2 meter use
• Testing of other power inverter brands and types
• Testing of ignition suppression wires
• Additional grounding studies
• Testing on 1.25 and 0.7 meters
• Using PSK31 during contests

35
References

• Your Mobile Companion, WF4N, ARRL, 1995
• PSK31 2000, WB8IMY, QST, 5/2000, pg. 42
• Automotive RFI Elimination, WA6PDP, QEX, 1/2000,
  pg. 32
• PSK31 on the Road, W9QQ, QST, 3/2000, pg. 55
• PSK31 software download from http//users.nais.com
  /jaffejim/mixwpage.htm
• Assembling Your Station, G3SEK, The VHF/UHF Book,
  1992
• ANC-4 Manual, JPS Communications, 1/1996,
  www.timewave.com
• Accuvolt Manual, Jacobs Electronics,
  www.jacobselectronics.com
• CN25 Ignition Suppression Wires,
  http//www.magnecor.com
• Ground gain and radiation angle at VHF, 0Z1RH,
  http//www.qsl.net/oz1rh/
• ANR-4 review, QST 2/1996, pg. 78
• MFJ-1026 review, QST 4/1998, pg. 73
• FT-847 review ,QST 8,1998, pg. 68
• IC-706-IIG review, QST 9/1999, pg. 80