1. VHF Antenna Construction
Jim Nelson
K9QF
9/20/2018

2. Introduction Licensed in 1976 as WD9BKC BSEE 1981
Lake County RACES member 1985
Major HR interests include:
50Mhz & higher “All Mode” & DX
Antenna experimenting & construction
PA’s, Batteries/charging, Power Supplies etc.
Foxhunting was the hook
Antennas are manageable size at VHF
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3. Agenda Focus on VHF Antennas for FM
Most likely needed to participate with LCRACES
Discuss the issues regarding Permanent, Go-Kit, & “Survival” antennas.
Where to scrounge for materials.
Ideas on how to put them together
Talk about techniques that don’t require a torch, just basic hand tools.
Materials readily available at the hardware store.
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4. Overview Why do you need an Antenna anyway?
And why that “Rubber Duck” just won’t do.
Review of some basic Antenna theory
Materials and techniques
For those who don’t have a machine shop
Gain
Impedance
Feedline
DBi
SWR
Polarity
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5. Why do you need an Antenna anyway?
Irritate your neighbors
Get to know your village officials
Piss-off your wife
Give your ride that squad-car look
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6. Why do you need an Antenna anyway?
Irritate your neighbors
Get to know your village officials
Piss-off your wife
Give your car that squad-car look
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7. Why do you need an Antenna anyway?
Provide an efficient transducer for the electrical signals to/from the transceiver / feedline into the atmosphere.
Provide a suitable load for the transceiver.
Speaker/microphone, incandescant lamp/solar cell
Ant. Is bi-directional.
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8. Some basic theory
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9. Some basic theory Resonance is a good thing 9/20/2018
Organ pipes, guitar strings
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10. Some basic theory Resonance is a good thing
A non-resonant antenna will radiate – but not nearly as efficiently
Woofer / tweeter at wrong frequency
- show springs
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11. The Dipole 9/20/2018 Ohms law, low Z etc. Feed point impedance.
How to get on a car?
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12. The ground plane 9/20/2018 36 Ohms – Oh no what to do?
Compare to dipole – fold down radials
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13. Improving the impedance
(A) Needs beads. Really a dipole bal/imbal.
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14. What’s gain? The DB DBi DBd 9/20/2018
Logarithmic – relationship between values. 10log Pout/Pin
3db double in power, 10db=10x
BI-DIRECTIONAL
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15. Where does gain come from?
It ain’t free!
No power cord
Balloon example
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16. So how much gain does my Rubber Ducky have?
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17. So how much gain does my Rubber Ducky have?
Can be as low as –30 DBd
Mfr. claims under ideal conditions
Radio itself may be limiting
Body proximity
*Ham-cram teacher
Minimal counterpoise
Absorption
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18. Applications Permanent install Transportable (Go-kit) Improvised
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19. Permanent install Mechanical durability Weather Appearance 9/20/2018
Accessibility for repair – but may not be abusive as mobile.
SS hardware is worth it
Do the neighbors think it looks like crap?
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20. Transportable Easy assembly / disassembly Durable in transport
Adaptable mounting
Common connections
Doesn’t need to weather
Not permanent mounting but safe
Screws / nuts bad
Fragile? Mounting versatility?
Electrical / RF hazard
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21. Improvised From car / other sources Material on hand
Spare parts are a good thing
Common mounts allow you to steal from car
Stripped coax
Coat hangers
Cross band repeat to car
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22. Practical examples
Show and tell materials.
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23. Practical examples The infamous SO239 The easy 3/8”x24 stud
Mirror bracket and gutter mount
Get to know your plumbing dept.
Forget Joan Crawford –
I Love wire hangers!
Coax or antenna? It’s both!
Go for silver & Teflon
Common CB hardware
Flex & ridged dim. Not the same.
Brass welding rod OK but hard to solder
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24. Practical examples
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25. Practical examples
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26. Practical examples
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27. Practical examples
From QST article
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28. Reference info: Step drills: Harbor freight # 91616-1VGA $8.87
Thread files #1&2 Enco / $6.69 ea.
5/8 antenna
J-Pole references:
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29. Reference info:
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