[CQ-Contest] 4 Square/ Raised Radial Questions

[David Robbins K1TTT]

How can the current on the outside of the shield of the coax upset a phasing
network that is in an all metal box?


David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
 

> -----Original Message-----
> From: cq-contest-bounces at contesting.com [mailto:cq-contest-
> bounces at contesting.com] On Behalf Of Joe Subich, W4TV
> Sent: Tuesday, January 29, 2008 06:52
> To: k1ttt at arrl.net; CQ-Contest at contesting.com
> Subject: Re: [CQ-Contest] 4 Square/ Raised Radial Questions
> 
> 
> 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 at contesting.com
> > [mailto:cq-contest-bounces at contesting.com] On Behalf Of David
> > Robbins K1TTT
> > Sent: Monday, January 28, 2008 5:04 PM
> > To: CQ-Contest at 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 at arrl.net
> > web: http://www.k1ttt.net
> > AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> >
> >
> > > -----Original Message-----
> > > From: cq-contest-bounces at contesting.com [mailto:cq-contest-
> > > bounces at contesting.com] On Behalf Of Robert Shohet
> > > Sent: Monday, January 28, 2008 13:20
> > > To: CQ-Contest at 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 at earthlink.net
> > >
> > >
> > >
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