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Stop Jamming Yourself
and Let the Weak
Signals Through!
Rob Renoud – K3RWR
Mid Atlantic States VHF Conference
September 27, 2014
1
Agenda
• The Problem
• The Culprits
• Troubleshooting Tools
• The Payoff
2
The Problem
• Designed EME station from ground up
– Goal: Competitive 2 meter EME station
– Best practices from weak signal community
• First ARRL 2012 EME contest
– Finished middle of pack with 34 Q’s
– W3SZ logged 125 Q’s
– Worked everyone displayed and decoded
– Why the difference?
3
The Problem Cont’d
• Suffering from “Low SNR”?
• SNR (dB) = Signal (dB) – Noise (dB)
• Everyone maximizes signal
• What about minimizing noise?
• Goal: Identify and eliminate noise
• Payoff? Wait and see!
4
Digital Paging Transmitters
• Symptoms: Random increase in background
noise level
MAP 65 Wide Waterfall
Light blue streaks
indicate increased
noise level
5
Digital Paging Transmitters Cont’d
152 MHz Digital Pagers (3)
WKIK – FM: Tower located
1/3 mile from QTH 170 MHz Unknown
2M Amateur Activity2M EME Center Freq
RF Spectrum @ K3RWR6
Digital Paging Transmitters Cont’d
• Pair of 4” bandpass filters on each RX line
• Decibel Products
148-174 MHz filters
• Bottom 300 KHz of
2M band
• Brute force approach
(pagers: >S9+60 dB)
7
• Before and after comparison:
After cavity
filters installed
Before cavity
filters installed
8
Digital Paging Transmitters Cont’d
Video Monitor Modes and Cables
• Six monitors and two computers
• Monitor cables identified as major RFI sources
• Video modes and observed RFI:
– VGA: Extremely noisy
– HDMI: Moderately noisy
– DVI: Low noise
• Converted all monitors to DVI
• A case of self-jamming resolved
9
LED Video Monitors
• 3 – 6 dB noise increase <15 deg elevation
• Blamed on “urban environment”
• Isolated to pair of 24” LED monitors
• Exchanged monitors with XYL
• Another case of self-jamming resolved
24” LED
Monitors Off
24” LED
Monitors On
10
Internet Router & Ethernet Cables
• Joel Harrison, W5ZN, paper: “Slaying the GrimReaper of Internet Router Noise”
• Multiple Ethernet cables @ K3RWR
• Turned off router
– 50% of birdies disappeared
– Noise floor dropped by 5 dB
• Migrated to wireless connectivity
• Installed toroid cores per W5ZN paper to one remaining wired Ethernet connection
• Another case of self-jamming resolved
11
Power Line & Impulse RFI
• High power line & impulse RFI prevented 6
meter ops at previous QTH
• Incorporated SDR-IQ receiver into shack
• Running Linrad or Winrad software
– excellent noise reduction capabilities
• Placed first in several meteor scatter contests
with this approach
12
13
Noise Blanker
Off
Noise Blanker
On @ 10%
Tools
• Spectrum analyzer (Rigol DSA 815)
• 2 meter Yagi and battery powered RX
– Arrow Yagi antenna
– Kenwood TH-6F handheld (SSB rx mode)
– Laptop running WSJT / MAP65
14
Payoff
• Unbelievable!
• 2013 ARRL EME contest:
– 112 total Q’s versus 39 Q’s the previous year
– Still have a lot to learn about contesting and EME, but now am a player
• Encourage everyone to search out and eliminate noise sources
• Questions / Comments?
Thank you!15