Since you are using a using a tuner at the feedpoint, the resonant
frequency isn't too important. The antenna you have should be resonant
somewhere around 2.0 MHz which is probably the reason you are using a
tuner. Changing the vertical section to a cage moves the resonant
frequency to 2.4 MHz and at 1.85 MHz decreases the real part of the
feedpoint impedance by about 1.2 ohms. EZNEC says the cage also
decreases the gain by about 1 dB. Part of that is 0.3 dB more ground loss.
Notes:
Cage was four #12 wires in a square, 4.5 ft between wires. I assumed 10
ohm ground loss in both cases, modeled over real average ground with an
almost perfect radial system and a loss resistor. Numbers calculated
above will vary with the ground loss number. Mininec ground cannot be
used with this antenna. EZNEC is very touchy when trying for an
accurate answer. Average gain error test is required. Numbers less
than 1 dB are of questionable accuracy.
Jerry, K4SAV
n9lah@comcast.net wrote:
> At the risk of fire up the cage machine again one related question. What will
> changing the 55 foot vertical section of my inverted "L" to a 6 wire cage
> from a single wire do? It is 55 feet tall supported 4-5 feet from my tower.
> The horizontal section is probably 70 feet long and slopes down to about 20
> feet and the antenna is tuned with an SGC 237 tuner at the feed point.
>
>
>
> I guess my question really is if it would really help much for the work
> involved.
>
>
>
> Phil
>
> N9LAH
> _______________________________________________
>
>
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|