Force12 – C3S
6 elements 20/15/20m
Testing at Ground level
The idea is to make an
initial measurements before installation on the 6m mast, prior to
final installation on the tower.
As the antenna is 3.5m x 11m, with a weight of 12Kg, and as i have no tower for easy installation, it is better to have some idea how the antenna is tuned, how it reacts in order to minimise the time spent to rise up/ rise down the antenna !
At only 2m from ground, the earth effect is important, as well as surrounding area.
Force12 @ 2m up
clearly shows that too many surrounding elements will not help, in a
small garden !
In that position, deep point are found on each bands (20, 15, 10) with incorrect SWR, impedance and bandwidth ! (see below for curves)
Prior to Force12, I made the 5el LFA (G0KSC) adjustement, and an idea I never used before was used : pointing the yagi to the sky ! The result was fine on the LFA, so why not on this one !
Force12 – C3S pointed to the sky for adjustement
On this antenna, the feed point is only on the 20m driver element, where 10 and 15m « drivers » are working as opensleeve dipole. So installed like the picture, despite of the 20m reflector is very closed to the ground (few centimeters), the curves show deep point SWR on the 3 bands, and permit to have a better idea how the antenna is tuned ! (see curves). The key advantage of this method is to tune the antenna without rising it for each adjustement !
However, before making the first adjustement, I prefered to rise the antenna on a 6m mast to verify if I can really use this method. So after few minutes, the antenna is installed on the mast, and rised !
Force12 – C3S @ 6m for adjustement
Force12 – C3S - Comparative curves for each bands
As you can see, the antenna is quite well adjusted on 20 and 15mn where the 10m is really to high for a CW operator. As the measurements show quite the same result, it seems that I can do some adjustement with antenna pointed to the sky, before a final verification on a 6m mast (which will save energy!)
To be continued...
http://f5ad.free.fr/ANT-QSP_F5AD_Baluns.htm#Filtre de gaine (ou choke balun)
Haubanage Pylône et Verticale :