quad reflector versus yagi reflector

[bob85]

NB.
i have heard a very similar sounding method of tuning claimed to have been used on keydown mobiles, not by the guys that were winning,

Am i reading your words as you meant them to be understood ?,

You tune the driven for lowest vswr, then without altering the driven again just add a reflector & tune the reflector for best front/back, then add directors as many as you like using the same method without adjusting the other elements to compensate,

if thats what you are saying can you explain how your tuning method works when mutual coupling detunes the elements as you bring them close to each other ?.

 

[Marconi]

What did you use to generate your design dimensions?
Oh, I just use an SWR meter & an S-meter to tune. Start with the Driven, make it's length 1005/freq in MHz and cut until lowest (2:1) on the SWR meter.
Add Reflector (1030) & cut until max F-B is attained using a beacon & S-meter.
Add 1st Director (985), tune the same way as the Reflector.
Add additional Directors & tune the same, one @ time.

Back in the early days I tried making a single element quad. I started with some parts from a buddy that had a 3 element. I borrowed his support parts for his driven element and he said it tuned very well so just use these parts and you should be in business.

I could never get that thing to tune below the red on my SWR meter. I added wire and I cut the wire maybe 20 times, but nada for the match.

Now I think I know why that thing did not work as a single element, it apparently has a very bad match as a single element that cannot be fixed just by adding or cutting the wire.

The attached Free Space models below seems to confirms this.

However, in the real world of antennas your mileage may vary.

NB, the formulas you provided do work however, and are very close when the reflector, driver, and at least 1 director is included in the mix, and all the elements are spaced out effectively. It seems all these parts of a beam work together and not independently like your method of tuning suggests.

So it looks like Bob is right...unless you left out a step or two in your process.

 

[Marconi]

NB.
i have heard a very similar sounding method of tuning claimed to have been used on keydown mobiles, not by the guys that were winning,

Hey Bob, maybe the reason those guys never won was because they spent all their time tuning and missed the events.

 

[Captain Kilowatt]

Back in the early days I tried making a single element quad. I started with some parts from a buddy that had a 3 element. I borrowed his support parts for his driven element and he said it tuned very well so just use these parts and you should be in business.

I could never get that thing to tune below the red on my SWR meter. I added wire and I cut the wire maybe 20 times, but nada for the match.

Now I think I know why that thing did not work as a single element, it apparently has a very bad match as a single element that cannot be fixed just by adding or cutting the wire.

The attached Free Space models below seem to confirms this.

However, in the real world of antennas your mileage may vary.

NB, the formulas you provided do work however, and are very close when the reflector, driver, and at least 1 director is included in the mix, and all the elements are spaced out effectively. It seems all these parts of a beam work together and not independently like your method of tuning suggests.

So it looks like Bob is right...unless you left out a step or two in your process.

IIRC the impedance of a single loop is somewhere arount 100 ohms or a little higher.

 

[Marconi]

CK, you're right, the match looks to be a little different over real Earth and likely depends on height to some degree, but the impedance is still high.

 

[Marconi]

What did you use to generate your design dimensions?
Oh, I just use an SWR meter & an S-meter to tune. Start with the Driven, make it's length 1005/freq in MHz and cut until lowest (2:1) on the SWR meter.
Add Reflector (1030) & cut until max F-B is attained using a beacon & S-meter.
Add 1st Director (985), tune the same way as the Reflector.
Add additional Directors & tune the same, one @ time.

NB, you say you cut until you got below 2:1 SWR. My model of the single quad element set using 1005/27.205 = 110.8" inches produces 4.134 SWR at the feed point. I added wire to make it longer to reach resonance, so maybe your word "cut" was just a figure of speech. The SWR did go down to 2.576 SWR, but no lower when the software figures the match at the feed point.

If you were using a feed line or jumper it might have shown you less than 2.00 SWR.

So what you claim here could work according to the steps I took with my model following the process you set out for the single element.

Then I added the reflector using your formula and made the wire longer and the rejection improved to nearly 30 db down, so I stopped. The gain also dropped a little as might be expected. However, the match went back up to 5.387 SWR and now the driven element looked too long. This was because I added length. In spite of knowing the antenna to be long I left it alone...thinking my adding the director element #1 to the driver and reflector might lower the SWR, but that did not help. NB, this is where your process starts to fail on my model.

I had to fix the reflector and the driven element back to where the formulas indicated, and for the first time the model's SWR dropped into the workable range. After adding and additional director #2 and #3 the match was 1.256 SWR, but this antenna has a very narrow bandwidth at 0.80 MHz.

So, my questions.
Did you actually cut or was this just a figure of speech?
Did you use a feed line to tune?
What was the bandwidth?

Again, Reflector-1030/freq in MHz, Driven-1005/freq in MHz, Directors-985/freq in MHz for starters.

Based on my models, you saying it this way makes more sense, and then start tweaking for better gain, rejection, or match.

 

[wavrider]

http://cb-antennas.com/?page_id=207

Good reading here, dimensions,gains,spacing etc

 

[Marconi]

NB, here is my Quad model with 4 elements that is based on the formulas you posted. I used the Quad Calculator by N6ACH on the Internet for the spacing.

I added the Free Space results also. You will see this model shows a very good match and I added a actual length feed line too. In the real world this design might need a little tweaking when installed over real Earth.

 

[Needle Bender]

Nice models.

Frankly, I'm a little surprised at what I thought was more of just an offhand comment becoming the main jist of this thread.

...and I had to chuckle to meself when I saw that, with all the questioned fine details being tossed around, NOBODY even iterated ANYTHING about the Velocity Factor (VF) of the wire, one of the MOST IMPORTANT variables in ALL of the equations! LoL

I like modeling, used to spend hours on the computer back when I was competing in car audio, trying to figure out that perfect "magic bullet" enclosure design to give me another +3-5dB, and I DID, even had a "World record" (in my arena of competition, not the Guiness book - lol) but only after I used the modeling to get me in the ballpark then brought it into the real world of wood, saws, screws, glue & metering, and made the necessary changes based on real-world variables which the modeling didn't predict, such as boundary loading, cab resonance, cab flex, enclosure flex, varying Q coefficient of SPL compressed air, etc...

Again, I like modeling but only to get you into the ballpark, the rest is up to the designer/builder to translate into the real world, and how well one accomplishes THIS is the measure of the man, and the results will speak for themselves.

When I would bring my Quad on the air, the 5 words I heard most from locals, some of whom already had beams such as 3 el & 4 el Yagis or PDL-IIs, was, "Would you build me one?!" - and not because it exhibited only mediocre performance.

On one I built I ended up having to cut the natural rubber coated stranded 12Ga Driven element down to 33' 4" before I could even begin to get it into the ballpark of tuning.

How's THAT figure into your modeling? 100" per side??

-That wire calculated to having only around a 92% velocity factor!!!
- "Who'd uhv thot, EH?" (For Beardyman 'In the Kitchen' )

Yep, I tore my hair out for almost a week over that build/tuning because I "KNEW" from calculating and formulas that it "HAD TO BE LONGER!!"

That was Ed's 5 element and to this day I've not been nearly as impressed by even an 8 element store-bought a friend had up for almost a decade.

Modeling be damned! Calculations & formulas will get you in the right State & County, but it's up to you to bring it into the right City block.

Correctly executed "Hands-on" beats theory, hands down, everytime.

.

 

[Marconi]

Needle Bender in my earlier comments I suggested that you must have left something out in the description of your tuning process. My model used no insulation on the wires.

But I can add this consideration to the model, but it will not show the wire reduction length of 100" inches any where near like you claim in your words.

Yep, I tore my hair out for almost a week over that build/tuning because I "KNEW" from calculating and formulas that it "HAD TO BE LONGER!!"

See, if you had consulted with me I could have maybe figured out your problem or give you something else to consider. Maybe that would have saved your hair the wrath of your ignorance at that time. Science does work and has a place in the human experience. But I'm not saying that science is always the answer...the reprobate minds of men mess that theory up.

Correctly executed "Hands-on" beats theory, hands down, everytime.

Like I state in my antenna motto in the signature area of my posts.

We're just lucky that Mother Nature doesn't require our antenna systems to be perfect in order to work our radio.​

 

[Captain Kilowatt]

Modeling be damned! Calculations & formulas will get you in the right State & County, but it's up to you to bring it into the right City block.

Correctly executed "Hands-on" beats theory, hands down, everytime.

.

Exactly my stance on modeling. Modeling cannot be accurate for all installations and the ONLY way to achieve optimum results is thru trial and error. Mostly error and learn from it.

 

[Marconi]

Exactly my stance on modeling. Modeling cannot be accurate for all installations and the ONLY way to achieve optimum results is thru trial and error. Mostly error and learn from it.

Of course Captain, modeling should require the ability to duplicate the predictions in real life or the modeling is considered dubious. The same is true of hands on testing as well, don't you think?

 

[Needle Bender]

See, if you had consulted with me or Bob we could have maybe figured out you problem and saved your hair the wrath of your ignorance at that time. Science does work and has a place in the human experience.

Those were all built in & around 1988-1990 without the benefit of a computer or a network analyzer. Basically, all I knew was the simple ballpark wire size formula and that a full-wave loop should be around 100Ω (2:1 swr) and that element spacing should stay within .125 to .25 wavelength. The rest was learned by "fire & error".
I did know the insulation had a tendency to affect the wire VF but the one & only Quad I built with bare wire produced noticeably higher rain static and was rebuilt later that year, in the Spring, with 12ga THHN.

 

[Needle Bender]

Of course Captain, modeling should require the ability to duplicate the predictions in real life or the modeling is considered dubious. The same is true of hands on testing as well, don't you think?

I believe it's because of past hands-on experience we have formulas & modeling, but real-world is still my preference, though modeling certainly can help get one in closer than a ballpark guesstimate.

 

[Marconi]

I realize you guys don't consider my modeling of any value, but don't think the tools are worthless in the hands of well qualified folks in this world.