[NLRS] 432 sprint and antenna stacking question

Sun Apr 25 17:00:38 EDT 2021

It’s a wonder I haven’t blown up more gear in the rover, with less than 4
feet of mast above the roof tower in the back of the pickup. I routinely
have 3 bands on there, sometimes up to 5, all around 100w give or take.
Have definitely experienced interactions though and lost at least  one
preamp.

Need to come up with a better arrangement- perhaps a telescopic mast that I
can quickly extend and lower when I stop.

Good article!
73 W0ZF

On Sun, Apr 25, 2021 at 3:20 PM JamesDuffey <jamesduffey at comcast.net> wrote:

> Mike - The capture area is not the same as the antenna physical area for
> most antennas. The capture area is related to the antenna gain by A=
> (Gain*(wavelength)^2)/(4*pi) where gain is a pure number, like 2, 4, or so
> on, not in dB.
>
> For antennas based on half wave elements, like the Yagi, the capture area
> is an ellipse with a horizontal to vertical dimension ratio of about
> 1.33:1.  For a dipole the capture area is given (approximately) by
> A=0.13(wavelength)^2. This is an ellipse with a minor axis of about 0.5
> wavelength and a major axis of 0.67 wavelengths.
>
> For Yagis you can get a good idea of the capture area by just multiplying
> the capture area of a dipole by the gain over a dipole, (in pure numbers,
> not dB). Then you can use the formula for the area of an ellipse to get the
> major and minor axis.
>
> This may be more than you wanted to know.
>
> The kicker is that to determine the stacking distances one needs to know
> the capture area (Gain) of both antennas on both bands, which is something
> that needs to be calculated with a program like NEC. - Duffey KK6MC
>
> James Duffey KK6MC
> Cedar Crest NM
>
> > On Apr 25, 2021, at 13:43, Mike Cizek W0VTT <mgcizek at gmail.com>
> wrote:re
> >
> > Thanks for posting that, Bill.  This is the best explanation I have
> seen for
> > interaction between closely spaced antennas.
> >
> > I have one question about calculating degradation when one antenna is
> within
> > another's capture area.  Do you look at the antennas in a 2 dimensional
> > plane?  i.e., calculate the area of the boom as seen from the end, and
> the
> > length of one element?
> > OR - do you need to look at is as 3 dimensional and include the surface
> area
> > of EACH element, like you do for wind load?  I' trying to squeeze my VHF
> > antenna in between a couple of HF antennas.
> >
> > ----
> > 73,
> > Mike Cizek W0VTT
> >
> > -----Original Message-----
> > From: nlrs-bounces at mailman.qth.net <nlrs-bounces at mailman.qth.net> On
> Behalf
> > Of Bill ND0B
> > Sent: Sunday, 25 April, 2021 11:36
> > To: 'Mary Brown' <maryalanab at gmail.com>; 'NLRS' <nlrs at mailman.qth.net>
> > Subject: Re: [NLRS] 432 sprint and antenna stacking question
> >
> > Hi Mary,
> >
> > I used this is guidance when I put up my antennas.
> >
> >
> https://directivesystems.com/information/tech-notes/multiple-loop-and-yagis-
> > on-one-mast/
> >
> > I have 6m, 222, 2m, and 432, in that order, stacked on the same mast that
> > extends about 15 feet above the tower.   It is definitely not optimal but
> > does provide enough isolation that I have yet to pop a preamp.    Part of
> > the spacing was mechanical issues, the 6m and 2m antennas both have
> guying
> > systems so the 222 antenna was placed just above the 6m guy mount, the 2m
> > was spaced down from the top such that there was room for the 70cm
> antenna
> > above it.   This arrangement did not flagrantly violate any of the
> guidance
> > DS offered and it seems to be working as I have yet (emphasized) to pop a
> > preamp.
> >
> > 73 de Bill ND0B
> >
> >
> >
> > -----Original Message-----
> > From: nlrs-bounces at mailman.qth.net <nlrs-bounces at mailman.qth.net> On
> Behalf
> > Of Mary Brown
> > Sent: Friday, April 16, 2021 4:30 PM
> > To: 'NLRS' <nlrs at mailman.qth.net>
> > Subject: [NLRS] 432 sprint and antenna stacking question
> >
> > I will be on for the sprint from en24gp.
> >
> >
> >
> > And question on stacking. I need to put 222, 432, and 23cm on one tower.
> >
> >
> >
> > Antenna and half stacking distance
> >
> > 222-10ez 3' 3" half stacking distance
> >
> > 432-9wl 3' half stacking distance
> >
> > 23cm35x4 on an H frame 1' 2 1/2" half stacking distance
> >
> >
> >
> > Thoughts were 222 on the bottom 2' above the tower
> >
> > Then 23cm35's 4'5" above that
> >
> > Then the 432 antenna 4'2" above those
> >
> >
> >
> > According to DX Engineering mast load this will survive 120mph.
> >
> >
> >
> > Thoughts? Going to be running power on 432 with 750 watts and 23cm with
> 550
> > watts,  so interactions? Preamp issues from the RF fields? Preamps will
> be
> > below tower top so it will just be whatever the antenna picks up from the
> > other bands.
> >
> >
> >
> > Would love to space this more but this is going on a bracketed Rohn 25 on
> > the side of the house. right at max wind load.
> >
> >
> >
> > Mary
> >
> > W0AAT
> >
> > ______________________________________________________________
> > NLRS mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/nlrs
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:NLRS at mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
> > ______________________________________________________________
> > NLRS mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/nlrs
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:NLRS at mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
> > ______________________________________________________________
> > NLRS mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/nlrs
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:NLRS at mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> NLRS mailing list
> Home: http://mailman.qth.net/mailman/listinfo/nlrs
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:NLRS at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html