One side of the dipole and the feed makes 76 feet, not far from 66 feet
which would be a half wave on 40. Even with the slightly short radiator
on 40, it makes a low impedance that transforms through just over a
quarter wave of 600 ohm feed line to something high so the tuner arcs.
If the dipole was 60 ohms, it transforms to 6000 ohms through a quarter
wave of 600 ohm feed. 100 watts at 6000 ohms is 775 volts. If you cut
those feed line spacers in half to get a 300 ohm line or doubled the
conductor size to get a 300 ohm line, and were those spacers for #14?
Wire size is a part of the impedance formulas. With a 300 ohm feeder
that low antenna impedance would transform to only(?) 1500 ohms so the
voltage would be 1/4 what your getting. I see www.73CNC.com claims 14
THHN makes 600 ohm line. 600 ohms takes 4.48" spacing, 300 ohms takes
0.406" spacing.
73, Jerry, K0CQ
On 2/13/2011 6:17 PM, tom stewart wrote:
> OK,
>
> Many came to my aid when I asked for suggestions. I made some choices and
> built an antenna. I tried hard to maintain spacing and avoid metal by at
> least a foot. It did not come out well so I need help. Here are the details
> if anyone has some suggestions I would be grateful-again.
>
> 1. Purchase "Ladder Snap" spreaders to build 600 ohm feeder.
>
> 2. Purchased plenty of 14 gauge THHN wire.
>
> 3. Because of room constraints, the legs of my inverted Vee are 31 feet.
> Center is 35 feet high and the legs end at about twenty feet.
>
> 4. Legs to feeder is continuous- feeder is 45 feet from center and
> terminated by grounded shield coax through window pane(vinyl).
>
> 5. Tuner is for now an MFJ balanced- model 974-I think.
>
> 6. reactance is high on all bands. It will only tune up on 14MHZ. tuner
> arcs if I persist at 7mhz
>
> 7. readings with antenna analyzer are as follows:
>
> Readings are at the bottom of the bands beacause I operate CW only.
>
> 7.020mhz r57 x158 swr 10.0
>
> 10.110mhz r168 x 135 swr 6.0
>
> 14.020 r21 x58 swr 7.5
>
> 18.075 r20 x70 swr9.1
>
> Thanks in advance- I know it is difficult to say with this limited
> information but I am at my wits end- about 10 hours into this
>
>
> Tom N7ESE
>
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