QUAD Beams - Are they better than Yagis? Are thicker 'wires' better?
Summary
TLDRJustin G0KSC from Innova Antennas discusses his Quad Yagi Antenna (LFAQ) design, inspired by Yu7XL's work. The LFAQ features adjustable elements for precision and a twin boom design for rigidity and high power handling. Justin covers the antenna's design parameters, benefits like high gain and broadbanding, and its comparison to traditional Yagi antennas. He also addresses the limitations of NEC-based modeling for curved elements and the practicality of the LFAQ for various power levels and frequencies.
Takeaways
- 🌐 Justin G0KSC is the creator of Innova Antennas and shares his designs on his website g0ksc.co.uk.
- 📚 His work is featured in the ARRL Antenna Book and in the DUBUS magazine.
- 📅 In 2021, he covered quad Yagis in DUBUS magazine, which is part of the discussion in the video.
- ⏰ The video might be split into two parts due to YouTube's time limit for videos from channels with fewer than a thousand subscribers.
- 🎯 The main topic is the design and inspiration behind Justin's quad or LF Quad (LFAQ) antenna.
- 🔍 The inspiration for the LFAQ came from YU7XL's antenna designs, particularly the use of solid rods clamped onto a boom.
- 🛠️ Justin wanted to make the quad elements adjustable to fine-tune the antenna's performance.
- 📡 The LFAQ features twin booms, which allow for easy adjustment and better performance stability.
- 🔩 The antenna design includes a break at the bottom of the driven element for feeding and an insulator for the coaxial cable.
- 🔗 The LFAQ is designed to be simple to maintain and can handle high power levels, making it suitable for various conditions.
- 📊 The video discusses the trade-offs between the number of elements in a Yagi or Quad antenna and their performance, including gain and bandwidth.
- 📈 Justin uses a slide to illustrate the effective gain per foot of boom and how it compares between Yagi and Quad antennas with similar bandwidths.
Q & A
Who is Justin G0KSC and what is his association with Innova Antennas?
-Justin G0KSC is associated with Innova Antennas and also operates the website g0ksc.co.uk where he publishes his antenna designs.
Where can one find Justin G0KSC's work published?
-Justin G0KSC's work can be found in the ARRL Antenna Book, D-STAR magazine, and his website g0ksc.co.uk.
What is the subject of the first part of Justin's discussion in the video?
-The first part of the discussion focuses on Quad Yagis and their design aspects.
What is the potential limitation of YouTube's video length for Justin's channel?
-YouTube limits the video length for channels with less than a thousand subscribers to around 15 minutes.
What is the inspiration behind Justin's LF Quad antenna design?
-The inspiration for Justin's LF Quad antenna design comes from Yu7XL's website, specifically the use of tubes or solid rods clamped onto a boom.
What is the main issue Justin has with the curved elements of the antenna design he mentions?
-The main issue is that curved elements reduce the accuracy of NEC-based antenna modeling, which could result in the antenna not performing as expected.
What is the purpose of making the tip lamps of the antenna adjustable?
-Making the tip lamps adjustable allows for fine-tuning the size of the elements to position the antenna exactly where needed.
What is the benefit of having twin booms in Justin's LF Quad antenna design?
-Twin booms allow for a single through-the-boom U-bolt on each side, providing stability and making the antenna easier to assemble and adjust.
How does the design of the LF Quad antenna help with static build-up and protecting the transceiver?
-The design includes an insulator running through the boom, which helps to remove static build-up and protect the transceiver by preventing electrical discharge.
What is the advantage of using larger diameter elements in a Quad antenna?
-Larger diameter elements can achieve higher gain and help to broadband the antenna, making it more efficient and stable.
Why did Clarence Moore W9LZX develop the Quad antenna?
-Clarence Moore W9LZX developed the Quad antenna to help remove higher altitude issues and prevent coronal discharge from melting the element tips of Yagi antennas.
What is the trade-off Justin considers when deciding the number of elements for a Quad antenna?
-Justin considers the balance between performance and the additional hardware, weight, and complexity. He finds that beyond seven elements, the performance benefit does not warrant the increase in these factors.
Outlines
📡 Introduction to Quad Yagi Antennas
Justin G0KSC from InnovA Antennas introduces himself and his work published on g0ksc.co.uk and in ARRL's antenna book and DUBUS magazine. He discusses the Quad Yagi antennas, also known as LFAs, which he will cover in depth in a potential two-part video due to YouTube's time limit for channels with fewer than a thousand subscribers. The inspiration for his design comes from optimizing Yagi antennas and the influence of YU7XL's designs, particularly the use of solid rods clamped onto a boom. Justin addresses the issue of model accuracy with curved elements and his solution of making the tips of the elements adjustable to fine-tune the antenna's performance. He introduces his design, the LFA Quad, which features twin booms for rigidity and the ability to adjust element sizes uniformly.
🔩 Design Features and Benefits of the LFA Quad
The LFA Quad design by Justin G0KSC includes a twin boom setup that allows for easy adjustment of the antenna's elements using U-bolts and insulators for secure coax feeding. The design helps to prevent static buildup and protect the transceiver while also providing a bandpass filter property. The antenna is robust and can handle high power levels, making it suitable for various environments, including icy conditions. The use of larger diameter elements contributes to higher potential gain and broader bandwidth compared to traditional quads made with thin wires. The historical context of the quad antenna's development by Clarence Moore W9LZX is also mentioned, highlighting its advantage in preventing coronal discharge issues that can damage Yagi antennas.
📊 Performance Considerations of Quad Antennas
Justin discusses the trade-offs between the performance benefits and the physical requirements of Quad antennas compared to Yagi antennas. He explains that while Quad antennas can offer higher gain, the need for more materials and the complexity of their construction must be weighed against the performance advantages. He mentions that he produces the LFA Quad up to seven elements and declines to go longer due to the diminishing returns on performance and the potential for narrow bandwidth issues. A slide is presented to illustrate the effective gain per foot of boom and the optimal number of elements for both Yagi and Quad antennas, suggesting that beyond seven elements, the performance difference is not significant enough to justify the additional hardware and weight.
🛠 Practical Aspects of Quad Antenna Design
In the final paragraph, Justin touches on the practical aspects of designing Quad antennas, including the challenges of feeding them with 50 ohm coax and the need to manage power handling and radiation. He presents an EasyNEC model of a short two-element Quad antenna for 144 MHz, which offers a compact design with good gain and front-to-back ratio. The discussion highlights the simplicity of direct 50 ohm feed compared to older designs that required matching networks, and the importance of considering the velocity factor of the coax when designing the feed point. The summary ends with a note on the continuation of the discussion in a second part of the video.
Mindmap
Keywords
💡Innova Antennas
💡ARRL Antenna Book
💡Dubus Magazine
💡Quad Yagi
💡Design Parameters
💡Yu7XL
💡NEC-based Antenna Modelers
💡Twin Booms
💡Gain
💡Bandwidth
💡Coronal Discharge
💡Stacking
Highlights
Introduction to Innova Antennas and g0ksc.co.uk website for antenna designs.
Justin g0ksc's work featured in ARRL antenna book and D-STAR magazine.
Discussion on Quad Yagi antennas and aspects to be covered.
Potential need for the presentation to be split into two parts due to YouTube's time limit for less than a thousand subscribers.
Design inspiration for the LFA Quad came from YU7XL's website and his antenna designs.
Challenges with NEC-based antenna modelers when dealing with curved elements.
Introduction of the LFA Quad with twin booms for better adjustability and performance.
Explanation of how the LFA Quad's design helps to remove static build-up and protect the transceiver.
Advantages of larger diameter elements for higher gain and broadband capabilities.
The Quad antenna's ability to handle very high levels of power.
Historical context of the Quad antenna's development by Clarence Moore W9LZX.
Comparison of the Quad antenna's performance to a Yagi antenna with similar bandwidth.
Practical considerations for the length of Quad antennas and their performance benefits.
Ability to stack Quad antennas for increased performance.
Introduction to EasyNEC and its role in antenna modeling.
Details on a short two-element Quad antenna model with a direct 50-ohm feed point.
Advantages of a 50-ohm direct feed for simpler antenna setup and power handling.
Performance metrics of a 144 MHz two-element Quad antenna model.
Conclusion and预告 of part two of the presentation.
Transcripts
hi
i'm justin g0ksc of innova antennas
and also the g0ksc.co.uk website
where a lot of my design work is
published or some of my older designs
are published for
free building yourself um you'll also
find some of my work in the
a r r l antenna book
and also in dubus magazine and dubus
magazine
in 2021 in the first part
i will be covering uh the quad yagis
and some of the aspects of what we will
discuss today
uh in an article there so please do take
a look at that also
um one thing i do need to to say at the
beginning is that this might need to go
over into two parts and the reason for
that
is at the moment whilst we have less
than a thousand subscribers
youtube tend to limit the time that you
can recall for so it's
it's around 15 minutes just over perhaps
but that's about the best that i can do
at the moment before we um
before we go into a position where um
they won't allow it to upload
so rather than having to try and trim
that
or cut it in half and produce two videos
it may be when it gets to that 15 minute
mark that i have to do that
okay so what we're going to be talking
about is my quad or
lfaq as i've designed it what
the design parameters were and why
and where that came from i've got some
notes here as well so i don't have to
sort of
add quite as many notations hopefully
onto the
presentation there afterwards so the
first thing really
is where did the inspiration come from
was very heavily
into optimizing yagi's and the
lfa yagi abdesyagi and so on which
you'll find on
some of the previous videos and
discussions about
but really the inspiration for this lfa
queue the the rigid
uh quad came from yu7 xl
now um bobin has a website which you can
find
at qslnet and uh he discusses
some of the various bits and pieces with
regards to his antennas
and at the bottom here he has a list or
a link where you can go to
where he discusses a great deal of the
the antennas
in detail you can click into one of
those and have a look at the details or
download the details
on that antenna and perhaps even build
yourself
so a very nice concept and if you look
it's using the tubes or
a solid rod that in this case is molded
and clamped onto a boom here
and then orientated onto a a long single
boom
now that idea is great the only issue
that i have with that is that
is that well in actual fact it's two
the first is that with easy nec or nec
based
antenna modelers mini neck modelers
marna gal when you have curved
elements as you do here that
reduces the accuracy of the model
and so what that means is that when
you're producing the antenna it might be
that you produce something as long as
this and it's not quite where you need
it to be
so you may have to either model it so
that it's very wide and lose a little
bit of the performance
or have to have a few different hits at
it
so one of the aspects that i wanted to
do was to
make these tip lamps adjustable so that
on all of those elements if the antenna
didn't sit exactly where you wanted it
to be
you could reduce the size of each of
those elements
or increase the size of each of those
elements all by the same percentage
so you could sit that antenna exactly
where you wanted it to be
the problem is with that is that when
you were to then
secure these element tips maybe with a
hose clamp or something like that
it would mean that these could easily
fold over
so what i produced is the lfaq
which would then have um twin booms
and we can see a first picture of one of
those here
this is a a 144 megahertz version
and as you can see it has twin booms in
this case
they're three-quarter inch this means
that you can just use a single
through the boom u-bolt on each side
and then the elements pass through the
top and the bottom now there is a break
at the bottom on the driven element so
that you can feed it
and there's an insulator that runs
through the boom so that the coax feeds
either side of the boom
but as far as electrically connecting at
the top that's fine at the design
frequency
that isn't seen so you've got the rf
travels around here hits this point
that's a point of
theoretical zero current come back again
just voltage
pick up the current go back with some
forward so we're going backwards and
forwards each side just like this
so at the design frequency that isn't
seen that helps
to remove the any static build up that
can
drain away and protect the the
transceiver and also
although it's not seen at the design
frequency it doesn't mean that the
antenna goes
uh high impedance very very quickly so
you have a bandpass filter that's
available filter property that's added
to the antenna too
so that's where it's at you can see then
there's just a single small bolt that's
needed to heat
up each of these to the elements here
and then the end sections uh there are
loops here with slide in trombone
sections like they are on the
lfa yagi which means that you can adjust
every one of them by the same percentage
to get exactly where you want to be
with that particular antenna so you know
it could be the case that
if you wanted to you could weld
those points once you're done or spot
world because there is the aluminium
brazing which you can use now with a hot
torch
and just simply effectively solder each
of those joints
and you're good to go the other
associated benefits with doing that
is as well i'm just looking at my notes
here to make sure i don't miss anything
this is obviously fairly simple to to
maintain
but when you have um traditional quads
they're generally made with thin wires
now one of the benefits of the quad of
course
is that per foot of boom it can be
higher than a yagi over a given if the
yagi and the quad have got the same
bandwidth associated with them
then of course it can be that there's a
higher gain figure
that does diminish and i'll show you in
a second why
um but with the
radiating element or the elements
themselves the thinner they are
the less gain there is it's very slight
but the bigger the element
generally the more gain that can be
achieved so of course when you have a
quad which lends itself to higher
gain and then you use thin wires you're
reducing potentially what gain you could
be having
so when you now get to and we can do
these on hf
but when you get these to vhf on you and
you're now using half inch elements with
3 8 inch end sections which is almost 13
millimeters
by 10 millimeters if you look at the
ends then the potential gain is much
much higher
and that also helps to broadband the
antenna as well
so what else was there um we spoke about
the gain part
um obviously it's strong and stable and
if you've got a fairly good bandwidth
which is easy to achieve with these
especially
with the larger diameter elements then
it becomes very stable as well so if you
imagine you had something like this in a
very very icy location
that can be loaded with ice and it
wouldn't be troubled at all
it's going to stay fairly rigid as well
and the other aspect is is that you can
handle very very high levels of power
now i'm just going to open up a slide
which i
delivered in a presentation and i'm
doing this rather than bringing them in
later because it feels more fluid if i
if i do these rather than overlay these
in the presentation later on
um the the the chord itself was
first introduced and developed by
clarence moore w9
lzx or w9 lzx
for our european friends and
the reason that he developed the quad
was to
help remove some of the higher altitude
issues that he had where he was
operating with the antennas
on a commercial station and coronal
discharge which you can see here on this
electricity cable
when you get very high power and that
happens on a yagi it happens at the tips
of the elements
and ultimately what that means is that
the element tips can melt and fall away
and then of course your antenna is no
longer um uh effective
frequency of operation will be on the
band where you were using it
because of course the elements would be
uh becoming shorter
so with the closed loop then
uh there isn't any tip that that can
that can be uh subjects to that
uh highest levels of coronal discharge
so you don't have the
the melting aspect that could occur as a
result
so um that was the the main reason um
for the introduction of the the quad but
of course it has other associated
disadvantages
if you look at the quad in the way that
i've produced it with the twin booms
and with the quad elements the quads
elements are
plus or minus depending on where you are
in the array
um a wavelength long whereas the yagi
elements
are a halfway vlon so when you're using
tubes you've now got twice as much tube
per element
as you would have with an equivalent
yagi
you also have two booms rather than the
one boom of the yagi
so it gets to a point where does the
performance that you're achieving
outweigh
what you're putting in so i'm going to
bring up another
slide which i made here earlier
to show you to which is very very basic
but to give you
um an indication as to where uh we are
as far as that performance
benefit is now commercially through in
of antennas we make uh the
lfaq up to around seven elements and
people on occasion say well could you do
me one longer could it be uh nine ten
twelve or or whatever it is
but i have a point of view with that and
one of the problems for me
is that um i said early on that i
wouldn't produce anything
commercially that i wouldn't be happy
with using myself
even if the the market demands it it's
like the
2 meter 70 sems yagi's on the same boom
no they're they're third harmonic
related so
if you're feeding with a single feed
point the two meter elements are going
to conduct when 70 sems is in use
which is going to flower petal the
pattern on 70 sems
so yes you can get a good swr but
you're not going to get the same
performance as you would do with other
dual band yards where you don't have
that third harmonic relationship issue
so it's a similar situation here if you
look at this scale here
we've got an effective gain per foot of
boom
in the vertical plane and then the
number of elements that you might have
on a yagi or a quad
so you can see when you've got a two
element a two element quad or two
element yagi
the difference that you would have in
gain
between the two is at its greatest as
the boom
gets longer that delta that difference
between the gain
between the yagi and the quad
starts to become closer together now for
me when you get up to sort of seven
elements
the the difference when you have an and
you can make
the game much bigger if you wanted to
but you're going to have narrow band
what i'm talking about is comparisons
between a yagi and a quad
which have similar bandwidth so
let's say 14 to 14.35
megahertz under say one point two to one
so that yagi and that quad both have one
point two to one from 14.0 to 14.35
that delta between those two points
for the additional hardware the
additional weight which is
is getting on for twice the amount in
the quad doesn't warrant
the difference in performance because
after all if i had the vertical space
i could then stack two of those yagi's
one above the other
and have a greater performance in that
single uh quad
okay so that's where we are uh on on the
quads and why i tend not to go
uh too long with these the other great
benefit with the quads
is the ability to be able to stack now
um what i'm going to do is i'm going to
open up an easy
neck version of the antenna and i'm
watching the time because we're already
up to 13.
um if you haven't got viewing
or any basic knowledge of easy neck or
some of the other modelling packages
this is available through easyneck.com
there is a free version
where you can buy and support the
developer the
the simple version and see some of these
in their fullness
and i will give some downloads to some
of these models which you can have a
look at
these will be presented on the screen
now and they'll be staying on my site
for you to be able to download
and play with now this is the a very
short
two element quad and it's a direct 50
ohm
feed point one of the things with the
older style quads is i always tended to
be around 110 112
ohm now i've come to the conclusion that
the reason it was optimized around that
figure
is you can use a quarter wave length of
75 ohm
piece of quarter wave length coax with
50 ohm coax at the end of it
that will give you a 50 0 match at the
end of that 75 ohm
length of coax but it needs to be
having the considerations of the
velocity factor of the cable so you need
to measure that to make sure it's okay
but the problem with that is of course
you reduce the power
capabilities of the antenna you need to
get it right
uh the the sizes that's involved for the
coax
and with a 50 ohm direct feed generally
you can have a shorter boom with a
similar
amount of gain perhaps in some cases
better amount of gain per foot of boom
once you get up to vhf and uhf getting
those
lengths of the coax correct and also the
power handling starts to become
a bit more of an issue and obviously
it's a great deal simpler to be able to
feed it
a quad with a 50 ohm coax and just have
to worry about a few
ferrite cores or a simple choke to stop
coax radiation
so when you look at this one this is for
2 meters 144 megahertz
and if i do the run here you can see it
gives
6.74 dbi 16
and a half db of front to back so it's
pretty reasonable
and when you look at the the boom length
it's just 14 centimeters long
i mean it's it's very very short indeed
and the reason it's that length is we
have to come in that amount
to keep the impedance fairly low i'm
going to need to chop this here
and i'll carry on in part two in just a
few seconds
you
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