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[GEORGEMINK]

I have a end fed random length in my attic already and I have purchased a folded terminated dipole to put in the attic as well.
The end fed is at the highest point I can get to and I thought I might run the dipole under the end fed. It would be about 3 feet below.
The other option is to run it along the side in the attic at a lower height but even then I'm still going to be 8 to 10 feet away from the wire
antenna just not under it. There is also the option of putting the dipole at a 90 degree to the long wire but that would have it emitting north and south not exactly what I'm looking for.

Any thoughts on how it would affect each other?

BTW I'm in a HOA that sucks so please don't suggest a 100' tower with stacked arrays I'd have that if I could. LOL

[K1VSK]

Proximity to the roof structure and any/all plumbing on HVAC generally has a greater effect than would another wire but as neither antenna would really be that directional, orientation isn’t a big consideration.

[GEORGEMINK]

Unfortunately my HVAC unit is directly under the wire antenna, and the duct trunk runs directly under it as well for 20' or more. It's the shinny Mylar flex duct so not sure how reflective it is but no way to get around it.

[K4FMH]

George,

I can't project to your attic arrangement. But I have several antennas within some distance of one another in my attic. I detailed the measurements for a Cushcraft D4 40-10M dipole in The Spectrum Monitor (see https://foxmikehotel.com/ and scroll down to the inline PDF to read it) last year.

I also have a T2FD about 4 feet away from the D4. It's quiet and low SWR from 160-6M (yep, there's a resister in the middle, etc.) but it serves the purpose when called upon.

My advice: install and take the RF measurement sweeps and adjust optimally according to those measurements. Alan W2AEW took a look at my preliminary results before TSM published it. He was highly surprised since I also have the "Oh no, it's a Faraday Cage foil-backed radiator barrier" installed. Experiment! I'm only sharing my experience.

73,

Frank
K4FMH

[KH6AQ]

There can be substantial coupling between the two antennas even if the feedline to one is open or shorted at the shack. We can model your installation in EZNEC to give an idea of how much coupling their is. Possibly the worse situation is the end fed coupling into the TFD which then burns off much of the power in its termination resistor. The two antennas at right angles will have minimal coupling. The safe bet is to install one antenna or the other. Or, install the two and see how it plays.

[WA3SKN]

I would try the 90 degree arrangement.
However, unless you plan to transmit with one antenna while receiving with the other it will not make much difference.  Try it!

-Mike.

[WB6BYU]

So much depends on not only the specific details of the
antennas themselves, but also the ducting, wiring,
roofing material, flashing, length of coax, etc.  It really
is difficult to predict, so sometimes you just have to
try it and see.

There are 3 general types of "interaction" to consider.

The first is signal pickup on one while transmitting
on the other.  If you aren't trying to use one on
receive while transmitting on the other, that's not
going to be a problem (although leaving a rig
connected to one while transmitting on the other
might not be a good idea.

The second is a change in SWR due to coupling
between them.  Since you are using a tuner with
the end-fed random wire anyway, that shouldn't
be a problem.  The terminated folded dipole should
be pretty broadband, but it is possible that the
long wire closely coupled to it might change the
SWR if the random wire (including transformer and
coax) happens to be close to resonance.  That you
will have to try and see.

The third cause of "interaction" is a change in the
radiation pattern.  Generally the antenna needs to
be somewhat close to resonance for the wire to
act as a reflector, and that will depend on the
frequency of operation.  But again, the ducting,
wiring, etc. is likely to be as much of a problem,
so we can only make a wild guess.


So I'd say put it up however is most convenient and
try it out.  Compare performance before and after -
if something seems really wrong, try one antenna at
a time, then both together to see if it seems to be
the other antenna or the attic environment  that is
causing a difference.

Even if the arrangement isn't optimum. it should
still radiate some RF.

[KE0VT]

Another possibility is to use Isotron antennas in your attic. They will be somewhat affected by all the metal. You can link any 3 bands on one feedline.
I have a homebrew Broad-Banded Terminated dipole. 70% of the input power is lost to the resistor, mine is 1K ohms. I have worked 6000 miles
south, east and west with the 25W out though.
With the BBTD you don't have to follow a straight line. My legs are 55'. No counterpoise needed, 500W if you wish and the Isotrons too! Let us know
how it works out! No tuner needed on the BBTD as it will be very broad banded.

73

[KH6AQ]

About 20 years ago AntenneX magazine published a two part article on the Isotron titled The Isotron Revealed Part 1 and The Isotron Revealed Part 2. A Google search finds the articles.

Isotron "antennas" aren't exactly antennas, they are antenna current excitation devices that use RF current on the coaxial cable shield and/or on the ground wire for the majority of their RF radiation. The Isotron/coax/GND wire can be thought of as a top-loaded vertical. Having said that, they can be decent antennas, especially when installed with all of this in mind. I would be cautious of placing an antenna inside the house that radiates along the length of the coaxial cable.

[K6BRN]

The biggest danger regarding coupling between the two attic HF antennas is damage to a second HF receiver attached to the receiving antenna while the other is TXing.  Avoid this pretty certain danger and you're free to experiment.

I've found that attic antennas are a major crapshoot.  As careful as you are, sometimes you get lucky, sometimes you don't.

Last year I put an EFHW-4010-2K up in a high peaked attic with the 63 foot wire strung in an approximate V shape, apex due South, apex at the peak of the roof on the south side and wire ends down a bit lower at the feed/wire ends to the North.  Dual common mode chokes were placed in series on the feedline just a few feet from the antenna, in contravention of usual practice for this resonant EFHW, where at least 7 feet separation between feedpoint and CMC is recommended.  A third CMC is placed near the operating station three floors below, which only has a basic safety ground system.  This contraption is fed with 75 feet of relatively lossy LMR-240 coax and is driven by a 500 Watt KPA-500, usually at no more than 350 Watts.

The roof is composite shingle and plastic air ducts, blown-in insulation and light fixtures with dimmers abound below the antenna, but there are no metallic linings on any of it.  The HVAC unit is three floors below, though the touch controlled washer/dryer and smoke alarms are on the floor just below the attic.

To my VERY great surprise, this setup works better that the previous (and compromised) outdoor, lower height tree to tree configuration of the wire antenna.  (when the trees both came down, so did the antenna). And there are NO detectable RFI/EMI issues.  Go figure.

Even the RF safety survey results close (the high peaked rook helps a bit here).

Interestingly, the 49:1 antenna matching transformer does heat up a bit on 40M, as it always did - but LESS than it used to.  The CMCs near the antenna actually get much warmer (never seen this before) which is why I use two to distribute the dissipation (yes, this actually works).  So nothing gets hot enough to overheat, even in 140F summer attic temperatures.  Most likely because this system is pretty lossy, I can also use the 10-15-20-40M wire antenna on 12, 17, 30 and 40M at reduced power - and make quite a few contacts.

THATS what I call LUCK.

I've made over 1,000 QSOs with it, out to just under 7,000 miles, with 2-3,000 mile QSOs being unremarkable.  Modes worked have been digital (FT8) and SSB (yes, sideband DX).  Seems to be pretty omnidirectional, according to PSKReporter RX mapping.  The present very good propagation conditions definitely help.  And so does the location right next to a large body of salt water.

But - I've seen others put in outside near-roofline and attic antennas that were nightmares and injected RFI/EMI into every circuit in the home, from the garage door opener to HVAC to lights and washer/dryer.

So experiment - and try improbable solutions.  You may get lucky, too.

Brian - K6BRN

[GEORGEMINK]

Thank you for all of the input.

I have two radios a FTDX3000 and FT991, I have a vertical out in the yard that I switch between the two radios and plan on having both the attic antennas assigned to the FTDX3000. Giving me a choice of 3 different antenna types to chose from based on the band, conditions, noise level, etc. The FT991 will see most of it's use on 2 meters and 70 cm. I have attic antennas up for that already.

Still not licensed so just listening in right now, just want to avoid any major issues when I do go live.

[K4FMH]

The biggest danger regarding coupling between the two attic HF antennas is damage to a second HF receiver attached to the receiving antenna while the other is TXing.  Avoid this pretty certain danger and you're free to experiment.

I've found that attic antennas are a major crapshoot.  As careful as you are, sometimes you get lucky, sometimes you don't.

Last year I put an EFHW-4010-2K up in a high peaked attic with the 63 foot wire strung in an approximate V shape, apex due South, apex at the peak of the roof on the south side and wire ends down a bit lower at the feed/wire ends to the North.  Dual common mode chokes were placed in series on the feedline just a few feet from the antenna, in contravention of usual practice for this resonant EFHW, where at least 7 feet separation between feedpoint and CMC is recommended.  A third CMC is placed near the operating station three floors below, which only has a basic safety ground system.  This contraption is fed with 75 feet of relatively lossy LMR-240 coax and is driven by a 500 Watt KPA-500, usually at no more than 350 Watts.

The roof is composite shingle and plastic air ducts, blown-in insulation and light fixtures with dimmers abound below the antenna, but there are no metallic linings on any of it.  The HVAC unit is three floors below, though the touch controlled washer/dryer and smoke alarms are on the floor just below the attic.

To my VERY great surprise, this setup works better that the previous (and compromised) outdoor, lower height tree to tree configuration of the wire antenna.  (when the trees both came down, so did the antenna). And there are NO detectable RFI/EMI issues.  Go figure.

Even the RF safety survey results close (the high peaked rook helps a bit here).

Interestingly, the 49:1 antenna matching transformer does heat up a bit on 40M, as it always did - but LESS than it used to.  The CMCs near the antenna actually get much warmer (never seen this before) which is why I use two to distribute the dissipation (yes, this actually works).  So nothing gets hot enough to overheat, even in 140F summer attic temperatures.  Most likely because this system is pretty lossy, I can also use the 10-15-20-40M wire antenna on 12, 17, 30 and 40M at reduced power - and make quite a few contacts.

THATS what I call LUCK.

I've made over 1,000 QSOs with it, out to just under 7,000 miles, with 2-3,000 mile QSOs being unremarkable.  Modes worked have been digital (FT8) and SSB (yes, sideband DX).  Seems to be pretty omnidirectional, according to PSKReporter RX mapping.  The present very good propagation conditions definitely help.  And so does the location right next to a large body of salt water.

But - I've seen others put in outside near-roofline and attic antennas that were nightmares and injected RFI/EMI into every circuit in the home, from the garage door opener to HVAC to lights and washer/dryer.

So experiment - and try improbable solutions.  You may get lucky, too.

Brian - K6BRN

Good for you, Brian! Experimenting is the key as attics vary widely but the presumption that nothing will work up there us the most powerful impediment. AC0C demonstrated this before he bought countryside acreage and put up towers.

73,

Frank
K4FMH

[AI5BC]

Anything within two wavelengths is going to affect the pattern and impedance of the antenna. If you cannot get an antenna at least 1/2-wavelength clearance above dirt, and 2-wavelengths horizontal clearance is going to be a compromised antenna. Less than 1% of hams have the means and skill to erect a proper HF antenna. UHF is easy.

[K5LXP]

I would probably substitute the word "perfect" for "proper".  Any antenna that achieves the operational goal is sufficiently "proper".  Don't let perfection be the enemy of good enough.  A compromise antenna that's deployed is better than a perfect one that isn't.

"Everything Works" - N6BT

Mark K5LXP
Albuquerque, NM

[K6BRN]

Anything within two wavelengths is going to affect the pattern and impedance of the antenna. If you cannot get an antenna at least 1/2-wavelength clearance above dirt, and 2-wavelengths horizontal clearance is going to be a compromised antenna. Less than 1% of hams have the means and skill to erect a proper HF antenna. UHF is easy.

The only organization I know of that has (close to) "no compromise" antennas is the government.  And even they bow to cost, schedule, etc.  An attic antenna is almost THE definition of a compromise antenna.  If it's simply omnidirectional and has >70% efficiency, THAT's a big win.  One that you can do a LOT with.

The real questions is: "Does it do what you want it to?"

Generally that desire is to "Get me on the air and work a lot of stations - and maybe participate in a few contents in a fun way".

Very do-able.

If the desire is instead "I want to crush the competition in every contest on Earth AND have my fellow hams is total AWE of my antennas.."  Well - that's not going to happen.  And it will take much more than a good antenna to do that.  Therapy is cheaper. 

So - nothing wrong at all with a compromise antenna.

Brian - K6BRN