[TowerTalk] "Q" (was no-subject)

[Maurizio Panicara]

Feed point impedance depends by several factors, not necessarily it's
required to detune elements compared to what they should be to obtain (i.e
max gain), to get also a convenient impedance for feed.
Deciding to derate a bit F/B because increasing the distance between driven
and reflector, a 2 elements yagi can be feed directly to 50 Ohm.
The cited compromises are sill nothing when compared with the measured lower
performance of antennas using traps.
Concerning a trapped element for feed, it's wise to keep in mind that traps,
when out of resonance are loading devices. The trap reactance is less than
that of the coil itself since the capacitive reactance deducts. A trap coil
is then bigger than that of a simple loading device and surely this doesn't
help to minimize losses.
Agreeing that an optimum parasitic spacing is desiderable, it's the same
desiderable that yagi elements carrying high currents have no devices (traps
& coils) that limit it.

73,
Mauri I4JMY

----- Original Message -----
From: <n4kg@juno.com>
To: <TOWERTALK@contesting.com>
Sent: Friday, September 22, 2000 1:39 PM
Subject: Re: [TowerTalk] "Q" (was no-subject)



> >
> > If that is the case, the solution would be to use a single trapped
> > driven element and perhaps separate full size elements for
> > reflectors and directors....or some combination of traps and full
> > size parasitic elements.
> >
> > So far, actual dissipative losses appear to be very low.
>
> SNIP
> >
> > 73, Tom W8JI
> > w8ji@contesting.com
> >
>
> Long ago, TELREX made a 2 element tribander, the TB4EM(?)
> which used a TRAPPED  Driven Element and separate full size
> reflectors for each band.  Looks like an interesting design to me
> that could be easily homebrewed using a Mosley or CC  DE.
>
> Note that the feed impedance of 2L Yagi's is higher than 3L
> which translates to less detuning to get a decent 50 ohm match.
>
> Wonder how that would compare with the C3S?
>
> de Tom  N4KG
>



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