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[VK3HAY]

I’ve had a sabbatical from hf and as you would guess my sgc tuner has failed,so no vertical atm
I’ve reinstalled a vertically polarised 40 meter delta loop and am loving the quite over the vertical.
However I’m wondering how close I could have a 20 meter dipole or inv v to the loop[or visa versa]
Only one antena is being used at any point of time.what sort of separation between them should I be looking at?
The 40 m loop is at 13 meters the 20 meter dipole could be up towards 16 meters high I’m thinking I should be able maintain a minimum of 5 meters and for the majority of the 20 meter up to 10 meters.
Any thoughts of issues I’ll be looking at[interaction etc]
Regards mark[vk3hay]

[WB6BYU]

Interaction is a complex question, which includes identifying
what sort of interaction you are concerned about, and specific
details of the antennas and installation.

Many hams have successfully run antennas in close proximity,
even interlaced.  The pattern might be distorted somewhat,
depending on the details.  Keeping the antennas at right angles
to each other will often help to reduce interaction.

In this case, if the dipole is mounted above the delta loop on
the same mast, the interaction will be greatest when the dipole
is in the same plane as the delta loop, and less when they are
at right angles.  Meanwhile, interaction will typically be less for
a vertically polarized loop, but the actual polarization response
of the loop on 20m will depend on the feedline connected to it
when the other antenna is in use.  (While the loop will be resonant
on 20m whether the feedpoint is open or shorted, the current
distribution around the loop will be different.  Any reactance
added by the coax stub will affect that as well.)

If you were using a beam antenna with a sharp rear lobe in order
to null out signals, the interaction would be more important, as
it could shift the null.  If you're just wanting a "generally
omnidirectional" radiation pattern, then a couple dB variation
probably won't make a significant difference in your operation.

The coax to the 20m dipole may affect the pattern of the delta
loop, depending how it is placed.  If it runs straight down the
mast in the center of the loop it probably won't be an issue.

So there are lots of unknowns.  I'd say your chances are pretty
good that it will work "well enough" with 5m spacing, so you can
try it and see.  Assuming you have the antennas installed using
pulleys and halyards (at least for the top of the loop), then you
can raise and lower the loop while listening on the dipole to
get an idea of the interaction.

[W1VT]

What I have done to minimize the interactions is to use modest gain antennas--no more than the gain of an extended double zepp antenna.
Three antennas in different directions typically is enough to work DX stations.  40 through 10 meters.

6 meters is the exception.  A 4 element beam near the house and away from the wires.  I tried running a 160M wire ten feet above the 20 ft high beam but the SWR rose to 2:1 when the beam was pointed toward Hawaii.

[VK3HAY]

Interaction is a complex question, which includes identifying
what sort of interaction you are concerned about, and specific
details of the antennas and installation.

Many hams have successfully run antennas in close proximity,
even interlaced.  The pattern might be distorted somewhat,
depending on the details.  Keeping the antennas at right angles
to each other will often help to reduce interaction.

In this case, if the dipole is mounted above the delta loop on
the same mast, the interaction will be greatest when the dipole
is in the same plane as the delta loop, and less when they are
at right angles.  Meanwhile, interaction will typically be less for
a vertically polarized loop, but the actual polarization response
of the loop on 20m will depend on the feedline connected to it
when the other antenna is in use.  (While the loop will be resonant
on 20m whether the feedpoint is open or shorted, the current
distribution around the loop will be different.  Any reactance
added by the coax stub will affect that as well.)

If you were using a beam antenna with a sharp rear lobe in order
to null out signals, the interaction would be more important, as
it could shift the null.  If you're just wanting a "generally
omnidirectional" radiation pattern, then a couple dB variation
probably won't make a significant difference in your operation.

The coax to the 20m dipole may affect the pattern of the delta
loop, depending how it is placed.  If it runs straight down the
mast in the center of the loop it probably won't be an issue.

So there are lots of unknowns.  I'd say your chances are pretty
good that it will work "well enough" with 5m spacing, so you can
try it and see.  Assuming you have the antennas installed using
pulleys and halyards (at least for the top of the loop), then you
can raise and lower the loop while listening on the dipole to
get an idea of the in\

Just to clarify the 20 meter is a dipole so can be lowered at will the loop is a 40 m vertically polarised on a 12 m pole…….the 20m dipole is on a seperate line so may at most cross over  the delta near a corner but a fair height above 5 to 8 meters…….thanks for pointing me in the right direction
Regards mark [vk3hay]

[G3RZP]

If you get hold of a copy of Frequency Synthesisers by Vadim Manassewich, it has a chapter on EMC within equipment, which includes equations for checking coupling between conductors. Below 30 MHz, you are unlikely to be in a far field situation, so the equations will give you a good idea. There's lot more been published in the IEEE  EMC journal over the years.

[K5LXP]

Practically speaking it's highly unlikely you'd encounter an installation where two antennas interact in any noticeable way.  If you think of a parasitic array like a yagi, even intentionally it takes specific lengths of conductors at specific distances for elements to couple efficiently.  Anything else is just a conductor in the field which will have some influence, but in all likelihood "not much".  No more so than any other random conductors that might also be nearby - house, power lines, fences, lawn furniture.  If you want an absolute number vs WAG with a model, you can transmit on one antenna and monitor the signal level on the other(s) and know band by band what the exact coupling is, and whether it's significant enough to warrant moving or reorientation.

Mark K5LXP
Albuquerque, NM

[WA3SKN]

Except for pattern distortions, I do not see an issue if you are using one antenna at a time.  Do you have them hooked up to separate radios and are using max power and not grounding the unused antennas?

-Mike.