Topband: Spitfire.......one more question

[Eduardo Araujo]

Many thanks Tom....excellent........as usual.

Unfortunately it is impossible to avoid the question.....

Good F/B is what I have with little gain which could coincide with your modeling.

Which could be the element dimension your modeling suggest to improve gain? Making the director longer to increase its current?  If is it possible for you to suggest some changes I would like to give them a serious try.  


Many thanks in advance for your time....... Eddie, LU2DKT




On Sunday, November 17, 2013 8:54 PM, Tom W8JI <w8ji at w8ji.com> wrote:
 
<<<<In order to detune the elements to allow omnidirectional radiation from 
the vertical, authors suggested to ground the elements where they are 
switched from director to reflector which will give you aprox 74.5 mts long 
element grounded at the base.>>>>>

You better have a good HV relay for that!

<<<<
In my case I have a relay installed at the corner of the elements which when 
opened leave only 53.6 mts sloping in the space from the top of the 1/4 wave 
tower to 40 mts from the base and 3 mts from ground. My question is, could 
it be possible instead of grounding it or leaving it opened, to add an 
inductor or a capacitor at that 53.6 mts point in series with the remaining 
element (24.0 mts for the reflector and 17.6 mts for the director) in order 
to make them invisible to the tower?>>

The relay requirements are much more reasonable at the point you are 
switching. With 1500 watts you have about 600 volts peak across the relay 
contacts and no significant pattern distortion. It is much better than the 
other method for everything, and requires no detuning capacitor or inductor. 
It has to be a good relay with good insulation.

My model shows the array slightly out of tune with those dimensions. The 
director is slightly low in current. But it has good F/B.