Hi Con,
In the early 1980's, I constructed a broadband receiving type "sloping
terminated V-Beam" for use on US Navy receiving sites in the 2-30 MHz
region. It had a few neat innovations and worked quite well. It was
duplicated at several receiving stations.
Basically, the legs were about 50 meters long and sloped from about 15-20
meters at the feed point to about 3 meters at the termination ends. The
apex angle was between 45 and 60 degrees (depended on installation). The
terminations were 400 Ohms at each leg to a ground stake. We used two 200
Ohm 2 Watt carbon composition non-inductive resistors at each leg to ground.
Perhaps the most interesting item was the feed system. I wound a Ruthruff
type 8:1 transformer (quintafilar wound). This was equivalent to an 800 Ohm
to 50 Ohm transformer. This allowed a 50 Ohm match with a reasonable low
VSWR over a wide bandwidth.
I hope this helps you.
73,
Joe, W1JR
t 11:52 AM 11/4/2001 +0100, corneliuspaul@gmx.net wrote:
>Hello
>
>Thanks to - Al and the others - for the fast responses. I think his answer
>(see below) pretty much sums up the post received so far...
>
>Well, I should have thought of it myself, that the resistors cannot add gain
>in the wanted directions, just cancl out "unwanted gain" in the other
>direction.
>...wishful thinking... well OK, it improves F/B ratio.
>
>Dont know whether your suggestions on a need for a ground screen
>apply to the unterminated version as well..?
>
>I have done some modeling on a so called v-star array already (several vee
>legs covering all directions) the patterns i came up with were not sooo
>promising, at least if one wants to use it as an all band antenna or
>at least for 4 harmonic bands.
>
>the apex angle is too narrow for the one band and too wide for the other band.
>the higher bands get higher forward gain but very narrow lobes..
>
>well... please keep your comments coming, i am looking for a directional
>allband wire antenna for traveling.
>(will probably look into an all band _inverted_ vee construction once again).
>
>73s, Con DF4SA
>
>
>k7puc wrote:
> >I have been using (and some studying) of vee beams for several years now.
> >Currently have a 500' long (each leg) with the apex at 100' high and the
> >400' points at about 50' then sloping down to about 20' high. The apex
> >angle is about 50 degrees estimated as I haven't been able to figure an
> >accurate and easy way to measure. The beam works pretty well on the higher
> >bands.
> >
> >My study has concluded several things:
> >1. If gain is the main consideration, then there is no need to terminate to
> >get unidirectional power because the power lost in the undesired direction
> >is used up in the terminating resistor.
> >2. The apex angle is quite critical i.e. my 50 degree angle is much to
> >narrow for 80 and probably also for 40 ( It has been a while since I modeled
> >this vee using EZNEC and am relying on my memory!)
> >3. I have not been able to resolve the statements "that the takeoff angle
> >can not be any higher than
> >the apex angle in degrees. For this reason, I don't know if having the vee
> >high is good or doesn't make much difference.
>
>
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