1. VHF/UHF Mobile Antenna System Decisions, decisions, decisions Mansfield Johnson Amateur Radio Service Sept. 4, 2015 by Bill Adams AF4B

2. Just the facts Efficiency is ratio of power radiated (or received) to power applied Maximum E and H fields occur with maximum RF current Maximum RF current flows when system impedances are matched 1:1 Antenna gain comes from shaping the electromagnetic field Short thick transmission lines have lower losses than long thin ones Reciprocity means performance is the same on transmit and receive Vehicle constraints force choices (compromise) Line of sight – you can see more from higher up It is difficult to get high efficiency on all bands of a multiband antenna

3. Efficiency Transceiver power out - Losses in feed line - Matching component losses - “Ground” losses Radiated power

4. Near ground level impedance of feed point Driven element lengthR Ω j Ω λ/436+21 λ/21100 to 1900-5000 to 0 5/8 λ≈ 50-50 to -150 R total = R transmission Line + R ground + R radiated

5. Gain Isotropic, λ/4, λ/2 and 5λ/8 elements ¼ λ pattern on vehicle (w8ji.com) 5 / 8 λ pattern on vehicle (w8ji.com)

6. Comparison λ/4 and 5/8 λ

7. W8JI’s conclusions http://www.w8ji.com/VHF%20mobile%20vertical.htm http://www.w8ji.com/VHF%20mobile%20vertical.htm With a normal mid-size roof contour 5/8th wave gain is now -4.64dBi at 2 degrees elevation. Maximum gain is now up slightly to 3.2dBi. With a normal sloped roof shape and mid-car size ground, the 1/4 wave has -6.59dBi at 2 degrees TO. Maximum gain is 3.05dBi. 5/8th wave gain is now 1.95 dB over a 1/4 wave antenna at 2 degrees, but the peak gain is only.15dB better! The smaller the roof and/or the less centered the antenna, the less gain advantage for a 5/8th wave. Lower height roofs also have less gain difference, and shape of the roof greatly affects pattern and gain. The 2.85dB theoretical gain is only for a perfect lossless loading coil antenna over perfect infinite flat ground plane. In the real world the actual gain difference between a 1/4 wave antenna and a 5/8th wave can be anywhere from the same up to a maximum of 2 dB. The 5/8th wave is never really worse, explaining why people have no problems using them. This is true for any repeater antenna height.

8. Transmission line Cable Flex versionsLosses dB/100’, MHzdB Losses in 6’ 1:1 SWR, MHz Dielectric / Shield type RG-174 Belden 82168.4 @ 100, 34.0 @ 10000.6 @ 146, 1.2 @ 443PE / Single braid Cu RG-58A Belden 82595.4 @ 100, 22.8 @ 10000.4 @ 146, 0.8 @ 443PE / Single braid Cu RG-8X Belden 92583.1 @ 100, 14.0 @ 10000.25 @ 146, 0.49 @ 443FPE / Single brain Cu TMS LMR240UF2.5 @ 100, 8.0 @ 10000.18 @ 146, 0.32@443FPE / Foil + tinned Cu braid RG-8 WM CQ1061.8 @ 100, 5.3 @ 10000.1 @ 146, 0.19 @443FPE / Foil + tinned Cu braid RG-8 Belden 82371.9 @ 100, 7.4 @ 10000.1 @ 146, 0.27 @ 443PE / Single braid Cu

9. Mounting location & vehicle size impact the pattern ( http://w6nbc.com/articles/2012- 03QST2mmounting.pdf ) http://w6nbc.com/articles/2012- 03QST2mmounting.pdf

10. http://ve2rmp.blogspot.com.br/2011/10/m obile-antenna-placement.html

11. Larson tech note on antenna placement http://www.pulseelectronics.com/products/antennas/larse n_antenna_products/technical_reference

12. Is the coverage significantly different? Coverage at 6’ above ground levelCoverage at 8’ above ground level

13. “Just tall – that’s all” Of course we are no longer mobile, but now vehicle portable.

14. How do you mount the antenna? NMO Requires a ¾” hole. SO 259 requires a 5/8” hole. 3/8 24 Ball mount requires holes! On glass – heard of passivated? Double sided 3M tape – ½ λ mandated due to lack of ground ¼ λ and 5 / 8 λ require ground plane Magmount requires iron, scratches surfaces, requires ½ λ antenna Garages and low clearance mandates folding design Driver side mounting preserves antenna!

15. NE5DL install of Diamond adhesive mount

16. Here’s what Gordo thinks about HF antennas

17. References http://www.k0bg.com/All things mobile, best reference I’ve found http://www.k0bg.com/ http://www.w8ji.com/VHF%20mobile%20vertical.htm and http://www.w8ji.com/end-fed_vertical.htm Source of several graphics used in this presentation http://www.w8ji.com/VHF%20mobile%20vertical.htm http://www.w8ji.com/end-fed_vertical.htm http://w6nbc.com/articles/2012-03QST2mmounting.pdf Mounting location impact on pattern http://w6nbc.com/articles/2012-03QST2mmounting.pdf http://www.k0bg.com/images/pdf/mobile_vhf_ant.pdf https://youtu.be/7gFNeW2Z1Xo NMO installation https://youtu.be/7gFNeW2Z1Xo https://youtu.be/u7YYaCgjfbs Overview of several antenna models https://youtu.be/u7YYaCgjfbs https://youtu.be/Fmm63d2Zyv4 Commercial antenna site https://youtu.be/Fmm63d2Zyv4