David,
> Personally I consider the shield of the coax (connected to
> the radials) to be one of the radials so why choke it anyway?
> Chokes at that point just add loss to the system when they
> try to block the current induced on the shield from getting
> back to the base of the vertical.
IF you take that view, you still want a choke on the phasing
network end of the line to the verticals. You do not want
radial current on the OUTSIDE of the coax (common mode current)
upsetting the phasing network. If we assume the phasing net-
work is properly designed (and that's another debate), the
common mode current will certainly upset the phasing, effect
the rear null and generally result in a degraded pattern.
73,
... Joe, W4TV
> -----Original Message-----
> From: cq-contest-bounces@contesting.com
> [mailto:cq-contest-bounces@contesting.com] On Behalf Of David
> Robbins K1TTT
> Sent: Monday, January 28, 2008 5:04 PM
> To: CQ-Contest@contesting.com
> Subject: Re: [CQ-Contest] 4 Square/ Raised Radial Questions
>
>
> The more radials there are the less important it is to tune them to a
> particular frequency. As was noted already the height is
> important if you
> are going to be picky. On my 4-square build last year I
> simply cut them so
> they were 1/4 physical wave long, just by measuring from the
> base where they
> were attached to one of the adjacent verticals, once you are
> past 3 or 4
> radials it probably doesn't make much difference if you cut
> them for one end
> of the band or the other.
>
> One thing that has me confused is your question about the
> coax. The coax
> (at least on comtek) has to be 1/4 electrical wavelength of
> 75 ohm foam
> coax. Any way you measure it adding ferrites on the outside
> should not
> affect the electrical length... if it does I would guess you
> are measuring
> it incorrectly or there is something wrong with the connector
> (ground not
> connected??).
>
> Personally I consider the shield of the coax (connected to
> the radials) to
> be one of the radials so why choke it anyway? Chokes at that
> point just add
> loss to the system when they try to block the current induced
> on the shield
> from getting back to the base of the vertical.
>
>
>
>
> David Robbins K1TTT
> e-mail: mailto:k1ttt@arrl.net
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>
>
> > -----Original Message-----
> > From: cq-contest-bounces@contesting.com [mailto:cq-contest-
> > bounces@contesting.com] On Behalf Of Robert Shohet
> > Sent: Monday, January 28, 2008 13:20
> > To: CQ-Contest@contesting.com
> > Subject: [CQ-Contest] 4 Square/ Raised Radial Questions
> >
> > Hi,
> >
> > I am in the process of fixing my 80 meter 4-square and
> > have some questions regarding raised radials.
> >
> > 1) Since my 4 square is "cut" for 3.65 and the radials need
> > to work on 3.5 as well as 3.8mhz, do I cut the radials
> > for 3.5 mhz with the thought that slightly too long (for 3.8 mhz)
> > is ok?
> >
> > 2) What is the correct formula for use with raised radials:
> >
> > Is it 246/f or 234/f?
> >
> > 3) The radials are all pvc coated. In theory this adds
> > 2-5% length to the radial or lowers the resonant freq.
> > by 2-5%. Any actual experience to confirm this?
> >
> > 4) If I use 3 - 4 radials on each of the four "legs",
> > does it matter how I orient the radials? Or, put
> > another way, if I am putting up radials for the SW leg,
> > do I want to orient the radials only in the S, SW and W
> > direction for that leg, or do I want to orient them
> > S, N, E and W?
> >
> > 5) I am using Seven 31 material ferrites at the feedpoint
> > of each "leg". The ferrites raise the resonant freq.
> > of the 1/4 wavelength coax about 20 khz as measured with
> > the MFJ 269. Should I cut for the resonant freq. WITH
> > the ferrites already in place, or should I cut and tune
> > before I put the ferrites on and then live with the change
> > in resonant freq.?
> >
> > Please let me know your thoughts and experiences on this.
> >
> > Tnx & 73,
> >
> > Bob KQ2M
> > kq2m@earthlink.net
> >
> >
> >
> > _______________________________________________
> > CQ-Contest mailing list
> > CQ-Contest@contesting.com
> > http://lists.contesting.com/mailman/listinfo/cq-contest
>
>
>
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