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