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(http://www.on8im.be/en/homemade/homebuilt-antennas/54-2-phased-verticals-array-40m.html) (/fr/realisations /realisations-antennes/55-verticales-en-phase.html)
22 PPhhaasseedd VVeerrttiiccaallss AArrrraayy 4400m m
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I build last week a Bazooka vertical for the 40m (see link here) (/en/realisations/realisations- antennes/53-1-4-vertical-azooka-antenna-for-the-40m.html) with good results.
This inspired me to build a second one and implement a two phased vertical array system.
I have chosen for a Christman phasing system : simple and easy o build
M Maaiinn m meennuu
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8
NNoow w,, pprraattiiccaallyy ... ssiim mppllee,, yyeess... bbuutt ...
I'll give you here how I made : probably there are better methods. I'm far to be a specialst ! First : start to build two identical vertical bazooka antennas
• Central frequency : 7.050 MHz
• Radials : system of 4 elevated radials 2m above the ground
• Coax used to build the antennas : used H100
• Top extension of the antenna (part C in the illustration below) : 300 Ohm Open Line shortcuted on both ends
• Measured coax velocity factor (*) : 0.82
(*) Don't trust to much the given velocity factor of the coax cables you have : the wise man will verify it with a antenna analyser (I use a MFJ 259-B), sometimes the results are verry surprising -espacialy with old cables laying in the shack since years, or little oxydated or often, the cheap cables coming from 'exotic manufactures'.
I used the formulas given in the page about the vertical bazooka :
A = (230/F)*0.305 (meters) = (230/7.050)*0.305 = 9.95 m B = A * Vf = 9.95 * 0.82 = 8.16 m
C = (A - B) = 1.79 m S = +/- 10 cm (not critical)
R = A * 1.05 = 9.95 * 1.05 = 10.45 m
Both antennas where built identical, mounted along fibergalss fishing roots and installed at abt 2 m above the ground
The SWR of both antennas didn't exceeds 1.2:1 on the entire 40m band.
TThhee pphhaassiinngg lliinneess ... aannootthheerr ssttoorrrryy...
λ/4 = 75/7.05 = 10.638 m 90° = 10.638
1° = 1.638/90
84° =(10.638/90)*84 = 9.93 m 71°= (10.638/90)*71 = 8.39 m Freq λ/4 = 9.93m => 7.54 Mhz Freq λ/4 = 8.39 => 8.94 Mhz Vel.fact coax. = 0.65
Lenght stub 84° = 9.93m*0.65 = 6.45 m Lenght stub 71° = 8.39m*0.65 = 5.45 m
Now, I cut pieces of coax a little bit longer that mentionned, I mounted a connector on one side, and left the other side open and determine with the MFJ-259B the correct quarter wave lenghts. You should find a dip and a value of X=0 or close to 0.
To be sure : I checked at conrresponding frequencies where my lenght of coax react as 3 or 5 quarter waves lenghts, I observed that the X =0 values are more prounonced at higher frequencies.
Example : if your dip is around 6.58 Mhz and indicate a X=1 or 2 , I try at 19.7 Mhz (6.58 X 3) : and I check if X=0 on this frequency, re-adjust if necessary. Repeat those measures several times before cuting in you coax.
Working at higher frequencies allow the work more accuately.
Once the coax pieces ready, I mounted the phasing lines and I used a coaxial relay , I didn't use the K1 relay like illustrated.
VVLLFF
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LLaasstt rreem maarrqqss ::
Your best ennemies :
the "T" SO-239 connectors (especialy the cheap ones comming from "exotic"manufacctures).
the PL-259 connectors, plse use professional quality (i.e. Amphenol) , incorrect assembly method of the connectors.
Making short : how more sophisticated, how more it must be assembled 'in the state of the art'.
M Meeaassuurreess ::
The measured SWR of phasing in both directions does not exceed 1.3:1 on the entire band.
PPrraaccttiiccaall rreessuullttss ::
A strong direction effect and a good F/B is observed.
See this demo video here (https://youtu.be/dmfNnC3Ybf8)
I made contacts with US stations, using only 50W SSB with succes. Not so bad ....
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