VHF Antenna Construction Jim Nelson K 9 QF

VHF Antenna Construction Jim Nelson K 9 QF 1 11/29/2020

Introduction Licensed in 1976 as WD 9 BKC l BSEE 1981 l Lake County RACES member 1985 l Major HR interests include: • 50 Mhz & higher “All Mode” & DX • Antenna experimenting & construction • PA’s, Batteries/charging, Power Supplies etc. 2 11/29/2020

Agenda l Focus on VHF Antennas for FM – Most likely needed to participate with LCRACES Discuss the issues regarding Permanent, Go-Kit, & “Survival” antennas. l Where to scrounge for materials. l Ideas on how to put them together l 3 11/29/2020

Overview l Why do you need an Antenna anyway? – And why that “Rubber Duck” just won’t do. Review of some basic Antenna theory l Materials and techniques l – For those who don’t have a machine shop 4 11/29/2020

Why do you need an Antenna anyway? Irritate your neighbors l Get to know your village officials l Piss-off your wife l Give your ride that squad-car look l 5 11/29/2020

Why do you need an Antenna anyway? Irritate your neighbors l Get to know your village officials l Piss-off your wife l Give your car that squad-car look l 6 11/29/2020

Why do you need an Antenna anyway? Provide an efficient transducer for the electrical signals to/from the transceiver / feedline into the atmosphere. l Provide a suitable load for the transceiver. l 7 11/29/2020

Some basic theory 8 11/29/2020

Some basic theory l Resonance is a good thing 9 11/29/2020

Some basic theory Resonance is a good thing l A non-resonant antenna will radiate – but not nearly as efficiently l 10 11/29/2020

The Dipole 11 11/29/2020

The ground plane 12 11/29/2020

Improving the impedance 13 11/29/2020

What’s gain? The DB l DBi l DBd l 14 11/29/2020

Where does gain come from? l It ain’t free! 15 11/29/2020

So how much gain does my Rubber Ducky have? 16 11/29/2020

So how much gain does my Rubber Ducky have? Can be as low as – 30 DBd l Mfr. claims under ideal conditions l Radio itself may be limiting l Body proximity l 17 11/29/2020

Applications Permanent install l Transportable (Go-kit) l Improvised l 18 11/29/2020

Permanent install Mechanical durability l Weather l Appearance l 19 11/29/2020

Transportable Easy assembly / disassembly l Durable in transport l Adaptable mounting l Common connections l Doesn’t need to weather l Not permanent mounting but safe l 20 11/29/2020

Improvised From car / other sources l Material on hand l Spare parts are a good thing l 21 11/29/2020

Practical examples 22 11/29/2020

Practical examples The infamous SO 239 l The easy 3/8”x 24 stud l Mirror bracket and gutter mount l Get to know your plumbing dept. l Forget Joan Crawford – I Love wire hangers! l Coax or antenna? It’s both! l 23 11/29/2020

Practical examples 24 11/29/2020

Practical examples 25 11/29/2020

Practical examples 26 11/29/2020

Practical examples 27 11/29/2020

Reference info: Step drills: Harbor freight # 91616 -1 VGA $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: //w 4 zt. com/jpole/ http: //www. fiu. edu/orgs/w 4 ehw/Jpoleant. pdf http: //www. vcars. org/tech/J_Pole 2 M. 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 28 11/29/2020

Reference info: 29 11/29/2020