5/8wave vs .64wave

[hotrod]

Needle bender, thats a wrong assumption.

The stallions model could indeed be improved.
But so where those of marconi and mine when i started.
(to CST) Dont be "irritated" you have already shown your willingness to deal with it..but it takes quite some time to do things rigth.

NB, your interpertation about the gain and lower take-off angle is based on a freespace model in which the gain will be less..however marconi is showing us a "real world" where a small effort from ground gain comes in place and the take-off angle is influenced by earth.

Another thing is as often people refer to SWR as it is often the only thing one can measure..but there is much more going on..

A groundplane can show a perfect 1:1 where at large portion is radiated in the earth. Where a good efficient groundplane can show a much higher SWR but in that case allmost all energy is actually radiated into the sky where it should be.

Ill give a examle:
The efficiency of a antenna is:
The antenna impedance/total impedance x100 procent.

The antenna impedance (in this case a 1/4 wave vertical) is 36 ohms:

Say we have a earth ground system of 14 ohms:
36/36+14x100 = 72 procent efficiency
BUT THE SWR WILL BE 1:1 as we have 36+14 ohms = 50 and matched to 50 ohms will show 1:1

Say we have the same vertical but now a efficient groundsystem in the order of 3 ohms.
36/36+3x100 = 93 procent efficiency!! but the SWR will be 50/39 is about 1.3

Oke, so what we have found out that a bad groundplane antenna can show a good SWR but will radiate poor.
We need to see 36ohm for the radiating element en preferbly a 0 ohm resistance in the groundsystem. In that case we have a high swr but a efficient system.

This is also the reason people claim high impedance antennas dont need radials.
Example: halve wave vertical (i take 1000 ohms as impedance could be a coulpe hunderd off though).

1000/1000+50= 95 procent. In this case i used 50 ohms for the groundsystem which is quite poor.

So, for the full quater wave vertical users...dont tune for 1:1 swr tune for that 36 ohms and more power will be transmitted in the air. (add to the groundsystem in order to lower that impedance).
As a perfect groundplane will show a SWR of about 1.3..1.4
Oke, so yes we have "reflected" power but thats only about 2..3 procent much less loss than the 1:1 system in which we were broadcasting about 20..30 procent in the earth.

Kind regards,

henry 19sd348
All about antennas

some very good reading.. now i just gotta transfer this into english so
a dummy like me can understand it....lol

 

[Henry HPSD]

@ CST you can download 4nec2 for free, which is sort of equal and will handle a lot more segements.

@ Marconi,

Looks like your old teacher was a wise man.

The model seems to be correct, but its not something for me now to really investigate.
(i need to type everything..which takes up time as you know).
If you are worried about anything just drop me the .ez file and i will look into it.
Just make sure the average gain is accurate and the segment lengths are equal.
Dont use two large different diameters and your probarbly in the safe zone.

Besides i dont know all....

I appologize, im quite bussy most of the time..still need to answer on that gizmotchythread
But dont worry i do check in from time to time and will reply if i believe something could be seen from a different point of view.

anyway i would like to say thank you for sharing your efforts regarding the models you put online im sure its appriciated by many...keep up the good work.

Kind regard,

henry
All about antennas

 

[Marconi]

When you can Henry. I'll email you the model.