VHF/UHF Dual Band J-Pole By: Ed Fong WB6IQN Email: Edison

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DBJ-2 Ed Fong 12/14/2013VHF/UHF Dual Band J-PoleBy: Ed Fong WB6IQNemail: edison fong@hotmail.comARRL VHF/UHF Antenna ClassicsARRL Vol. 8 Antenna CompendiumARRL Vol. 3 Antenna CompendiumQST March 2007QST February 20031

DBJ-2 Ed Fong 12/14/20132

DBJ-2 Ed Fong 12/14/2013Why a J-pole? J-pole configuration - no radials Ground plane requires radials – high wind load Very close to an ideal dipole pattern3

DBJ-2 Ed Fong 12/14/2013 First introduced to the ribbon J by AE6C in1990 Antenna excellent - considering simplicity Stick it in a PVC 3/4” - very durable Will last for years since PVC is UVprotected. To date – we have delivered over 10,000 Price to performance - excellent4

DBJ-2 Ed Fong 12/14/2013 It will also resonate at odd harmonics Ah ha!!! It will also work at UHF Very poor performance because of phasecancellation Typically 6-8 dB of loss at 3rd harmonic Goal is to design a dual band J-pole butwithout the loss New design must be simple, reproducible,no radials due to wind load.5

DBJ-2 Ed Fong 12/14/2013 No inductors, no capacitors, because theyare not easily reproduced. I tried all types of configurations, but thisone seems to work the best. Basically matching is the same at VHF andUHF. A 1/4 wave decoupling stub (RG174) is usedat UHF6

DBJ-2 Ed Fong 12/14/2013Smith Chartinductive 1jRepresents 1/2 wavelength once around0 ohms on left sideinfinity at right sidenormalized to 1 at center 2j0.5j10 ohms-2j-0.5jcapacitiveinfinity-1j7

DBJ-2 Ed Fong 12/14/2013300 ohm twinlead37 1/4”Cut out a 1/4” notch15 1/4”1 1/4”RG174a coaxSplice and short togetherFigure 1 The original 2 meter ribbon J-Pole.8

DBJ-2 Ed Fong 12/14/2013Figure 2 Horizontal pattern of fundamental and 3rd harmonic. At thethird harmonic most of the energy is launched at 45o.9

DBJ-2 Ed Fong 12/14/2013300 ohm twinlead17”Short topside of RG174a4 1/4” RG174a11 1/4”Cut out a 1/4” notch15 1/4”1 1/4”RG174a coaxSplice and short togetherFigure 3 The 2 meter J-pole modified for both VHF and UHF operation.10

DBJ-2 Ed Fong 12/14/20134” Nylon tie for hanging18”Short topside of RG174aCut out four 1/4” notches4 1/4” RG174a11 1/2”Cover these sections with heatshrinkable tubingCut out a 1/4” notch16 1/4”1 1/4”5 ft. of RG174a coaxSplice and short togetherBNC ConnectorFigure 4 The dual band J-pole modified for portable operation. Note thatdimensions are slightly longer due to the velocity factor of air.11

DBJ-2 Ed Fong 12/14/2013Notice that the dimensions on the DBJ-2 (roll up) are longer than theDBJ-1 (base station). This is because we have compensated for thevelocity factor of the pvc pipe.The pvc pipe used is very important. We found that Lowe’s item #23990 wasthe best performance for RF.12

DBJ-2 Ed Fong 12/14/2013Figure 5a 2 meter J-pole at UHF.Figure 5b DBJ-1 at at UHF.13

DBJ-2 Ed Fong 12/14/2013VHF ¼ wave mobileVHF rubber duckStandard VHF J-PoleDual Band J-Pole-24.7db-30.5 dB-23.34 dB-23.47 dBTable I Measured relative performance of the dual band antenna at 146MHz.UHF ¼ wave mobile-38.8 dBUHF rubber duckStandard VHF J-PoleDual Band J-Pole-41.3 dB-45 dB-38.9 dB14

DBJ-2 Ed Fong 12/14/2013Here I am in my lab using the HP8753D 6 GHz networkanalyzer.15

DBJ-2 Ed Fong 12/14/2013445MHzStub shows a clear resonant at 445MHz.16

DBJ-2 Ed Fong 12/14/2013445 MHzmarkerHands touching at shorted end. Graphs changes, but not 445MHz resonant point. Thissays I can place anything at shorted end without affecting the 445MHz resonant highimpedance.17

DBJ-2 Ed Fong 12/14/2013146 MHzmarker146 MHz marker of the UHF shorted stub.18

DBJ-2 Ed Fong 12/14/2013146MHz marker445 MHz marker of open wire.19

DBJ-2 Ed Fong 12/14/2013DBJ-1 mounted on the side ofthe roof.20

DBJ-2 Ed Fong 12/14/2013DBJ-2 kit – roll up dual band with BNC, SMA, and reverse SMA. Also6ft extension cable.21

1/2 λ¼λApprox. 50 ohm pointsRG174A cables¼λ½λCut out a 1/4” notch50 Ω feedpoint1/4 λvoltage and phasedistributionSplice and short togetherRG174a coaxto connectorThe two element UHF phase conlinear with the voltage and phase given on the right. Dimensionsare given for insertion into ¾ inch 200 PSI pvc pipe. US patent 8,947,31 3UHF Gain Antenna Ed Fong Pacificon 201022

DBJ-1 dual band base antenna - available in HAM (144-148 MHz and 440-450 MHz)or Commercial (152-157 MHz and 460-470 MHz) 25DBJ-2 dual band roll up antenna - available in HAM (144-148 MHz and 440-450MHz) or Commercial (152-157 MHz and 460-470 MHz) 25220 MHz base antenna - uses J-configuration fits inside a pvc pipe. 20UHF Gain Antenna Ed Fong Pacificon 201023

UHF Gain Antenna Ed Fong Pacificon 2010 22 ½ λ The two element UHF phase conlinear with the voltage and phase given on the right. Dimensions are given for insertion into ¾ inch 200 PSI pvc pipe. US patent 8,947,31 3 1/4 λ Splice and short together Approx. 50 ohm points RG

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