[Towertalk] F12 C4XL or C4SXL Which to buy?

[n4kg@juno.com]

The difference between using the Force 12 antennas on
the WARC bands and most others is that there are 
NO Resonant traps in the F12 antennas and
NO Tuned Matching Systems at the feedpoint.

The only losses in the split dipole feed system
are due to the additional feedline loss due to SWR.
IF the nominal feedline loss is LOW, then the additional
loss due to SWR is minimized.

A trapped tribander, especially with a tuned matching 
system such as the HyGain Beta Match would be
MUCH less effective on the WARC bands.

My investigation of 2L Yagi design revealed that
non-resonant parasitic elements will still provide
'some' gain (~2 dB) when placed at normal spacings.

Parasitic elements longer than 1/2 WL will act as
reflectors, even if MUCH longer than 1/2 WL.
Parasitic elements shorter than 1/2 WL will act as
directors down to about 3/8 WL below which they
become nearly transparent.

FWIW, parasitic REFLECTORS can be lined up
for each band with negligible interference.  I built
a 17 / 15 / 12M 2L reflector Yagi using a 17M
split dipole DE fed with Ladder Line back in 1985/6.

My model of a 5 Band reflector Yagi showed that 
gains peaked as expected on each band using
a single split dipole 17M DE fed with ladderline.

F12 has figured out how to make a 5 Band
coax fed DE in their new XR5 antenna.  I expect this
would be as effective as a medium size Log Periodic.

Tom  N4KG


On Thu, 07 Mar 2002  Peter Sundberg <sm2cew@telia.com> writes:
> Hi Tom.
> 
> Yes, I understand that, but my point is that advertising the antenna 
> as a 5
> bander opens up the opportunity to do the same thing for virtually 
> any
> antenna as anything at the end of a coax will radiate on 20-10 mtrs.
> F12's advertising should be questioned a little more in my opinion, 
> people
> think they buy an antenna for 5 bands when they don't. F12 sell a 
> tribander
> that is "forced" to run on WARC-bands, with properties that are so 
> poor
> that the antenna even shoots the other way on one band.
> 
> Anyone else advertising like they do would be flamed, but they get 
> away
> with it. Question is why..
> 
> 73/Peter SM2CEW
> 
> 
> 
> 
> At 00:31 2002-03-07 , you wrote:
> >A dipole does NOT need to be resonant to radiate,
> >so the split dipole feed on the C3 antennas is simply
> >matched at the transmitter through the coax on the
> >WARC bands.  Yes, additional feedline loss is incurred
> >but it does work.
> >
> >Tom  N4KG
> >
> >On Wed, 06 Mar 2002 Peter Sundberg <sm2cew@telia.com> writes:
> >> Fellow towertalkians, regarding Jims questions;
> >> 
> >> Am I right in assuming that the F12 yagis are designed for 20, 15 
> 
> >> and 10
> >> mtrs and 17/12 mtrs only work because there is a load at the end 
> of 
> >> the
> >> coax and you need to use a tuner to operate there..  
> >> Performance on those bands seems mediocre at the most. Kinda like 
> 
> >> stating
> >> that a 20 mtr monobander also works on 17 and 12 mtrs.. of course 
> it 
> >> does.
> >> 
> >> Or am I missing something ?
> >> 
> >> 73/Peter SM2CEW
> >> www.qsl.net/sm2cew
> >> 



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