VHF Antenna Construction Jim Nelson K9QF 9/20/2018

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 9/20/2018

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. 9/20/2018

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 9/20/2018

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 9/20/2018

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 9/20/2018

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. 9/20/2018

Some basic theory 9/20/2018

Some basic theory Resonance is a good thing 9/20/2018 Organ pipes, guitar strings 9/20/2018

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 9/20/2018

The Dipole 9/20/2018 Ohms law, low Z etc. Feed point impedance. How to get on a car? 9/20/2018

The ground plane 9/20/2018 36 Ohms – Oh no what to do? Compare to dipole – fold down radials 9/20/2018

Improving the impedance (A) Needs beads. Really a dipole bal/imbal. 9/20/2018

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 9/20/2018

Where does gain come from? It ain’t free! No power cord Balloon example 9/20/2018

So how much gain does my Rubber Ducky have? 9/20/2018

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 9/20/2018

Applications Permanent install Transportable (Go-kit) Improvised 9/20/2018

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? 9/20/2018

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 9/20/2018

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 9/20/2018

Practical examples Show and tell materials. 9/20/2018

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 9/20/2018

Practical examples 9/20/2018

Practical examples 9/20/2018

Practical examples 9/20/2018

Practical examples From QST article 9/20/2018

Reference info: Step drills: Harbor freight # 91616-1VGA $8.87 Thread files #1&2 Enco 990-3074 / 990-3075 $6.69 ea.   5/8 antenna http://www.arrl.org/tis/info/pdf/8009022.pdf J-Pole references: http://www.hamuniverse.com/jpole.html http://www.alpharubicon.com/elect/jpolejaden.htm http://w4zt.com/jpole/ http://www.fiu.edu/orgs/w4ehw/Jpoleant.pdf http://www.vcars.org/tech/J_Pole2M.html http://www.arrl.org/tis/info/pdf/9409061.pdf http://www.arrl.org/tis/info/pdf/0302038.pdf http://arrowantennas.com/inst/ijpole.html 9/20/2018

Reference info: 9/20/2018