[NLRS] 432 sprint and antenna stacking question

Sun Apr 25 16:20:14 EDT 2021

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
> 
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