HF Wire Antennas, EMI Contest Stations WCARC November 2016 VE 3 KL
Introduction A Top Down View of a Radio Station(s) 1. Wire Antenna Design. . . Ideas needed. . 2. Dipoles and Unwanted Radiation (EMI) 3. A Radio Station and Its Problems 4. Some Basics and Baluns 5. Designing a Contest Station (Field Day. . .
Wire Antenna Design Ideas(back of the envelope) 1. Tools well established Simulators, Analyzers, Vector Z meters 4 nec 2 (includes a very simple optimizer) TL Details, Sim. Smith, AIM 4170 connects to Sim. Smith 2. Missing: Advanced Optimizers
Wire Antenna Design Tools Many Tools Available 4 NEC 2 TOROIDs TLdetails Sim. Smith
The Ideal Fictious Antenna Only the antenna radiates Electric Field cuts across Feedline No Common Mode Current on Feedline No Radiation Common Mode Currents. . . . Currents that Radiate
A Basic Radio System Common mode choke here Mains choke Another choke here
Unwanted Common Mode Currents On the Outside of Coax • Causes Coax to radiate. . . poor SWR and distorted antenna patterns • Current gets into keyers, microphones, computers, routers and the radio • Reduce with line isolators/chokes/baluns
Coax Basics I 4, I 5 wanted radiation I 3 unwanted radiation (I 3 called common mode current) Compliments of GM 3 SEK
Coax Basics I 6 Two Sources of Unwanted Common Mode Radiating Current I 3. . . Right at the antenna/coax junction I 6. . . Direct radiation from antenna
What is a Choke (Also called a 1: 1 Balun, Line Isolator) PD 7 MAA A short section of Transmission line: 50 Ohm Wind it on a Ferrite Core = A 1: 1 Balun/Choke VE 3 KL FT 140 -43 RG 316 ZIP Cord 100 Ohm Good for 4: 1 Balun’s
What does “high performance” mean? Generally, high performance = high CM impedance For tough EMI problems, that means… several thousand ohms wide bandwidth mainly resistive (why? )
Contest Stations Field Day
OARC Corkery June 2016 15 m Dipole . . VHF, 6 m Yagi’s Vertical 40 m Windom End Fed . Vertical Multiband
Antenna Summary 1. Most Antennas worked as expected (Individually) 2. Strong EMI between the End Fed and Windom. . We worked around this problem with our 40 m Vertical thanks to Mike’s suggestion (VE 3 FFK) 3. Some EMI was experienced on the 6 m station! Maybe Phase Noise from an HF Transmitter. EMI Solutions ?
Causes of Interference (EMI) 1. Co-Resonant antennas closely spaced. . . Mutual Coupling Co-Resonant: Antennas resonant on same frequency 2. Received Transmitter Phase Noise and Harmonics 3. Currents flowing on outside of coax: Called Common Mode All of the Above can be addressed Let’s See How
Mutual Coupling (Remember the Yagi? ) Tx antenna couples a strong signal into nearby receiving antennas. . Zm [Ohm] Rx Antenna Receiver 5 W Ouch! Rx Overload Tx Antenna Transmitter 100 W
Mutual Coupling Basics. . Zm. Transmitting Receiving V 21 = I 1*Zm 80 Ohms Power, r /Power, t = [Zm/Z 11]^2/4 For Zg = Z 11 = Z 22 Coupling If Zm= Zg = 50 0 Power received only 6 d. B below power transmitted
Mutual Coupling If antenna spacing = 0. 25 Power Received = 12 d. B below Power Transmitted 80 Ohms Zm 0 Parallel Dipoles Spacing in Wavelengths
Mutual Coupling Co-Resonant (End Fed and Windom) 40 m Receiving Windom Approx. -12 d. B 20 m Transmitting End. Fed Power = 100 W [50 d. Bm] 38 d. Bm !!! d [ ] BIG Problem Yaesu FT-1000 D (40 m) Out of Band De-sensing Occurs at approximately 5 d. Bm RF Amplifier turned off
Add a Bandpass Filter at Receiver Helps Mutual Coupling Broad Band Receiving Antenna 40 m radio Approx. -12 d. B . 20 m Transmitting Antenna Power = 100 W [50 d. Bm] 38 d. Bm d [ ] Band. Pass Filter 45 d. B Rejection Problem Nearly Solved -7 d. Bm Yaesu FT-1000 D (40 m) Out of Band Blocking Occurs at approximately -5 d. Bm RF Amplifier turned off. . . turn on rx attenuator
Phase Noise Transmitter Phase Noise What is it? 1. All Oscillators have a small amount of nonwanted Phase Variation with time. Digital Engineers call this Clock Jitter 2. ICOM and others specify this in terms of noise power (d. Bc/Hz). . -140: 5 MHz from the carrier Noise Transmitted = Pc + d. Bc/Hz + 10 Log(BW)
Phase Noise Transmitter Phase Noise 40 m Receiving Antenna Approx. -12 d. B . -108 d. Bm in 40 m band d [ ] Band. Pass Filter 45 d. B Rejection 40 m receiver -120 d. Bm S 1. . . OK 20 m Transmitter Power = 100 W [50 d. Bm] Phase Noise 50 -140+10 LOG(500) = -63 d. Bm {in the 40 m Band}
Set-Up for All Stations Line Isolator here = “balun” Band Pass Filter “Mains choke” “Feedline isolator ”
Filter Implementation. . . Prototype Design from ELSIE 6 KV Capacitors Three Pole Big Toroids Butterworth. . Bandpass/Stop 100 W Fo = 14. 15 MHz
20 m Band. Pass Filter. . Three Pole Butterworth Measurements. . . Complements VE 3 ZRK
20 m Band. Stop Filter. . Three Pole Butterworth Measurements
Summary • Chokes are easy to make. . . use three might need small chokes at keyers, computers. . . • A ground stake is useful. . . lightning • Filters are essential for contest stations • Some EMI problems quite elusive
References/Acknowldegements • GM 2 SEK web site and drawings • ON 9 CVD. . a comprehensive web site on Ferrites and HF applications. • Parts and Kits. . . Toroid Supplier
73 Dave VE 3 KL
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