[600MRG] 630M - - My two cents

[Edward R Cole]

At 07:18 PM 1/22/2014, WE0H-Mike wrote:
>I still have my 45' vertical with 72' flattop rolled up from years 
>ago when I ran it on 1750 meters Part 5. I should use that for my 
>next vertical but not quite at 45'. Should be enough 'hat to make it 
>play on 600m just fine.
>
>Mike-WE0H
>WD2XGI
>XSH/16
>
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Mike,

That should work about the same as my inverted-L:  43x122 foot.  You 
will have less top-hat capacitance so will need a larger loading coil 
to bring the antenna into resonance.

The commercial NDB manuals show the "T antenna" with 60-foot high 
radiator and 300 foot long top hat wire.  The loading coil is small: 
1-inch dia x 5-inch (ferrite I believe).  I do not use that loading 
coil and couple out at 50-ohms into coax to a tap on my loading coil 
near the ground end.  NDB transmitter is mounted at the base of the 
vertical wire which connects directly.  No mention in the NDB manual 
of installing radials only a ground rod to the NDB transmitter.

I've wondered if one could put up an insulated 50 to 70 foot pole or 
tower with multiple wires like spokes off the top end (maybe sloping 
to work as insulated guy wires)?  If you put up six sloping guys with 
35 foot long top wires, would that equal the same capacitance as one 
wire six times longer?  If so a 60-foot by 6x 35-foot top-hat would 
equal a 60 x 210 foot "T".  If radials sloped 45 degrees the foot 
print on ground would be a 120-foot diameter circle.  Make the 
radials the length of the guy line base (60-foot) for convenience as 
full 1/4 wave length is 246/freq (MHz) = 246/0.475 = 518 
foot.  120x120 foot is 0.3 acre while 518x518 is 6.16 acres 
(acre=43,560 sq-ft)!  The antenna would look like a large umbrella.

My inverted-L has two 50-foot radials, a 70-foot radial and a 
110-foot radial (so they fit on my property). The long radial is my 
1-5/8 inch Heliax hardline from the shack to the tower that supports 
the inverted-L; the three other radials are 2-foot wide chicken wire 
fencing laid on the surface of the ground.  Antenna efficiency is 4%, 
Z = 0.81 - j681.5, measured impedance is Z=18 -j0 using my modified 
MFJ-269B analyzer.


73, Ed - KL7UWhttp://www.kl7uw.com
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