Quote:
Originally Posted by Wimpie
On 29 ago, 00:36, Owen Duffy wrote:
Wimpie wrote in news:1188313351.276557.292100@
22g2000hsm.googlegroups.com:
clipped... a nice description of an end fed vertical half wave with
matching network.
Wimpie, I think the OP had using the stationmaster radiator element
unchanged on lower HF bands.
You could view this as a 5.5m long radiator sitting on say, a 4m metallic
support mast, fed at the junction of the two. Typically the configuration
involves no radials at the base of the 5.5m radiator, and an shabby
connection to earth at the base of the supporting mast.
If at 80m you were to assume the earth resistance was as good as 30 ohms,
the earth loss alone would account for 60% of the power reaching the
feedpoint when the antenna is modelled without provision for current on
the outer of the feedline.
So, the StationMaster as described in the article is typically a ground
mounted ~1/8wl vertical with an inadequate ground system, elevated feed,
high sensitivity to noise, highly susceptible to RF in the shack unless
the feedline is decoupled adequately.
It is a little better on 40m, but all of the issues remain.
A lot of the guys wanting to do such a thing are our new six hour hams,
and they would be principally interested in 80 and 40m.
Owen
Hello Owen,
I was expecting that he would scale the design to another frequency to
assure half wave operation at the design frequency.
If one is really planning to do what you described (using the 5.5m
radiator from 80m..40m and upwards), it is a far from optimal choice
for transmitting. At 80m, the radiation resistance is still less then
2 Ohms, at 40m about 7 Ohms, so assuming 30 Ohm ground resistance will
result in a poor efficiency (about 6% at 80m and 19% at 40m). Off
course when one makes a large ground network, efficiency will be
better.
Best regards,
Wim
PA3DJS
www.tetech.nl |
My intention is to use this antenna on the 10 meter FM section of the band. I have been given a 1/2 wave "Ringo" antenna that is missing the ring. I intend to convert it to the "stationmaster" type antenna as I think it will be easier to get the matching system right using a coil spaced from the bottom of the radiator than try to make a new matching ring etc. Thus if I could locate plans for the making of such an antenna it would save me a fair amount of time in the calculations and cut and try type of antenna building.
The info collected so far is at least a starting point for the conversion of this antenna.
Thanks to all who have given input, it is greatly appreciated.
Mike
VK3XL