Beeing this a 2 elements yagi, the fed element will be shorter than it
would be alone and the amount of its shortening is not a fixed %,
likewise the reflector lenghtening. The boom lenght, infact, will also
play a consistent role in elements electrical lenght.
If elements loading isn't too lossy and boom not too long to further
reduce the moderate FB of a 2 el. yagi, the fed point impedance won't
be so close to 50 ohm but lower and some kind of matching device will
be required.
In the case such device is an hairpin, the dipole will be again shorter.
Before to proceed, a PC antenna modeling is highly reccomended.
73,
Mauri I4JMY
> A 5% lower resonant frequency for the reflector is a good place
> to start. It seems to me that one way to do this is to split and
> insulate the reflector and then either grid dip the element or
> measure the impedance at the center. Once it is tuned, then
> it may be joined and mounted to the boom. Yes, there may be
> some detuning effects but I would expect them to be small for
> a 40M element.
>
> 73 / GL, Tom N4KG
>
> On Wed, 5 Sep 2001 "K&L" <kmccourt@tbaytel.net> writes:
> >
> > Hi All , I am in the process of building a loaded two element 40
> > beam. I
> > have the driven element finished and its total length is 43` it is
> > resonate
> > @ 7.150. What would the most practical way to tune the reflector be
> > ? Should
> > I split & insulate the reflector , mount it on the boom and check
> > the
> > resonate frequency ? Is 5 % longer a good length ? I am not
quite
> > sure of
> > the best way method to use . Would like to get some input on this .
> >
> > 73 Kevin
> > VE3KKM
> >
> >
> > List Sponsored by AN Wireless: AN Wireless handles Rohn tower
> > systems,
> > Trylon Titan towers, coax, hardline and more. Also check out our
> > self
> > supporting towers up to 96 feet for under $1500!!
> > http://www.anwireless.com
> >
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|