[Antennaware] HF Colinear Dipoles

[k8mp at aol.com]

I also agree. My DXing antennas for the lower 3 bands are vertically polarized.


-----Original Message-----
From: dan edwards <w5xz at att.net>
To: Karin Johnson <karinann at tampabay.rr.com>; Terry Conboy <n6ry at arrl.net>
Cc: antennaware <antennaware at contesting.com>; weinfurt <weinfurt at ohio.edu>
Sent: Thu, Aug 29, 2019 01:05 PM
Subject: Re: [Antennaware] HF Colinear Dipoles


 agree 1000%, re paragraph 1...
73, w5xz, dan

    On Thursday, August 29, 2019, 11:55:50 AM CDT, Terry Conboy <n6ry at arrl.net> wrote:  
 
 Karin,

It’s hard to beat horizontal antennas on 20m and up due to the ground reflection gain.  Same for 40m if you can get a decent height (> .5 wl).

As for matching the switched 2-element collinear, after I sent out those models, it occurred to me that you feed them quite simply with 3/4 wl 75 ohm lines from each antenna, then in the shack, use two 1/4 wl 75 ohm lines connected in line with the two feeders.  For in-phase, feed at the junction of the two 1/4 wl lines (total 1 wl to each antenna) or for out-of-phase, feed at the junction of one 3/4 wl feeder and a 1/4 wl line (so 3/4 wl to one element and 5/4 wl total to the other).  Due to the mutual impedances, the elements are ~100 ohms in-phase and ~50 ohms out-of-phase, so this should give you 50 ohms at the common point for both patterns and switchable 0 - 180 phase with just a SPDT switch or relay.

There shouldn’t be a need for L & C matching, unless you are really picky about SWR.  Of course, if you use wider spacing between the elements, the element drive impedances will move closer to 75 ohms and things get more complex.

A bigger question that has always bugged me: why are there two L’s in collinear?

73, Terry N6RY


> On 2019 Aug 28, at 9:50 AM, Karin Johnson <karinann at tampabay.rr.com> wrote:
> 
> Hello Terry and Greg:
> I appreciate the responses and the models.  I also received an email from
> Gedas who pointed me in the right direction.  First off let me say I'm not
> a novice to this task.  Although most of my efforts on antenna design in
> the professional space have been in the 2 GHz and up arena.  I've actually
> got some patents on some of the designs.  With regards to that task HFSS, a
> very expensive modeling software is a joy to use.  Now with respect to HF
> antennas.  What got in the way for me was the matching task and the
> influence of one dipole on the other.
> Although the Low Band DXing book addresses verticals the basic concept of
> mutual coupling still exists.  You can see this effect if you model two
> collinear dipoles, look at the source data, then remove one of the dipoles
> and look at the source data.  The source impedance at the generator will be
> different.  Gedas sent me an article he wrote some time ago and this
> set off the light bulb in my brain.  From there I've been able to make some 
> progress.  The main reason for me doing all of this is curiosity.  Right now
> I have a 40 meter dipole in place and have recently put up a switched 80/40
> meter vertical.  I find that I am almost always using the vertical now and
> have toyed with the idea of a gain antenna for 20 meters to take the place
> of the 40 meter dipole.  I also have another 20 meter dipole that will
> remain in place but will be oriented 90 degrees to the collinear array if I
> decide to build it.  So for now this is mainly an academic exercise.  With
> regard to some of the simulations I have done with EZNEC I've found a really
> simple way to match both the in phase and out of phase arrangement of the
> two dipoles in collinear orientation.  It does require some vacuum relays at
> the junction point of the two feed lines but this is very doable.  I also
> need a 150 pF vacuum cap, and a small 0.25uH inductor.  I know vacuum cap
> probably is overkill but I tend to over design things. 
> 
> Regards,
> Karin  K3UU
> 

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