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Re-tuning a Sirio 4 element beam for 27.555mhz

Robb

Robb

Honorary Member Silent Key
Dec 18, 2008
11,432
3,653
323
Silicon Valley CA, Storm Lake IA
I sent a note to Sirio, asking how to change the tuning of the Sirio SY27-4 from 27.205 to 27.555mhz.
This is the response I received from Sirio.
Are their calculations correct?

"Dear Mr. Robb,

SY 27-4 is not a tunable antenna and SIRIO ANTENNE doesn't effect
substitutions and doesn't guarantee the correct working of altered products.

However, if you really want to try to change the work freq. of the antenna,
I can give you a method.

To work at 27.555MHz you must to RESCALE all length using this formula:


Final_length = (27.2 / 27.555) x Initial_length = 0.9871 x Initial_length

So:
REFLECTOR : New length = 0.9871 x 5740 = 5666 mm
DRIVEN: New length = 0.9871 x 5400 = 5330 mm
1 DIRECTOR: New length = 0.9871 x 5130 = 5064mm
2 DIRECTOR: New length = 0.9871 x 4890 = 4827 mm

Initially, I suggest to not rescale spacing between elements (only for
mechanical
possible problems) and verify the correct electrical working.

After the rescale you must to tune the antenna moving the gamma-match and
using a ros-meter (I can't help you now; the new position is not prevedible)

If the antenna don't work well, you can try to rescale also the spacing
between elements (using the same formula)

Reflector-driven: New length = 0.9871 x 1570 = 1550 mm
Driven-1 director: New length = 0.9871 x 1020 = 1007 mm
1 director -2 director: New length = 0.9871 x 1410 = 1392 mm

and re-tuning the antenna moving the gamma-match.


I remark that this is only a theoretical method and we don't guarantee the
correct working of antenna.

Best regards,

Ing. Mezzadrelli Lorenzo
SIRIO Antenne SRL..."
 
Last edited:

Robb said:
I sent a note to Sirio, asking how to change the tuning of the Sirio SY27-4 from 27.205 to 27.555mhz.
This is the response I received from Sirio.
Are their calculations correct?

"Dear Mr. Robb,

SY 27-4 is not a tunable antenna and SIRIO ANTENNE doesn't effect
substitutions and doesn't guarantee the correct working of altered products.

However, if you really want to try to change the work freq. of the antenna,
I can give you a method.

To work at 27.555MHz you must to RESCALE all length using this formula:


Final_length = (27.2 / 27.555) x Initial_length = 0.9871 x Initial_length

So:
REFLECTOR : New length = 0.9871 x 5740 = 5666 mm
DRIVEN: New length = 0.9871 x 5400 = 5330 mm
1 DIRECTOR: New length = 0.9871 x 5130 = 5064mm
2 DIRECTOR: New length = 0.9871 x 4890 = 4827 mm

Initially, I suggest to not rescale spacing between elements (only for
mechanical
possible problems) and verify the correct electrical working.

After the rescale you must to tune the antenna moving the gamma-match and
using a ros-meter (I can't help you now; the new position is not prevedible)

If the antenna don't work well, you can try to rescale also the spacing
between elements (using the same formula)

Reflector-driven: New length = 0.9871 x 1570 = 1550 mm
Driven-1 director: New length = 0.9871 x 1020 = 1007 mm
1 director -2 director: New length = 0.9871 x 1410 = 1392 mm

and re-tuning the antenna moving the gamma-match.


I remark that this is only a theoretical method and we don't guarantee the
correct working of antenna.

Best regards,

Ing. Mezzadrelli Lorenzo
SIRIO Antenne SRL..."
Click to expand...

I'm impressed. With the work load this company has, they will still take the time to have one of their top engineers answer questions about how to modify their product to fit your needs. No need to question this guys calculations, you got the information from someone that's well qualified. Overlook the English grammar, recognizing this is not their primary language.
 
Last edited by a moderator:
Shockwave said:
I'm impressed. With the work load this company has, they will still take the time to have one of their top engineers answer questions about how to modify their product to fit your needs. No need to question this guys calculations, you got the information from someone that's well qualified. Overlook the English grammar, recognizing this is not their primary language.
Click to expand...


Top engineer?
I didn't realize that.
If your impressed, then I'm impressed.

Now it's off to Home Depot tomorrow for a tape measure that has a metric scale - to make the job easier still . . .
Thanks!
 
Last edited:
Robb said:
Top engineer?
I didn't realize that.
If your impressed, then I'm impressed.

Now it's off to Home Depot tomorrow for a tape measure that has a metric scale - to make the job easier still . . .
Thanks!
Click to expand...

When I saw his name at the bottom of the letter, I recognized Mr. Lorenzo right away. He is the head guru at this company and possesses a wealth of information. He produced the CST model of the Vector and is responsible for much of the design work behind the new Gain-Master.

With respect to finding a metric tape measure at Home Depot, good luck Robb. Been there, done that with no success. If you have a "Dollar Store" around, that's where I found mine. Otherwise you may have to look online at places like eBay.
 
Shockwave said:
With respect to finding a metric tape measure at Home Depot, good luck Robb. Been there, done that with no success. If you have a "Dollar Store" around, that's where I found mine. Otherwise you may have to look online at places like eBay.
Click to expand...
Thanks for that tip too.
Sears is supposed to have them. I'll check there first.

I wonder how the gamma match adjustments will be different from the stock dimensions given in the directions/instructions. I will be using an MFJ 259 analyzer. But I was wondering how the shorter antenna will change the dimensions of that gamma.

I know that there are TWO adjustments on a gamma. The first thing to adjust is the capacitor length; then the attaching point to the radiator.
 
Since you are already adjusting the element lengths to compensate for this small frequency change, I would not expect the gamma to tune much differently from the stock setting. It would be ideal to tune the gamma in the antennas mounting position however, I'm sure you know that's not always practical.

If you're forced to tune the gamma on the ground, it should be done in an open area with the antenna pointed straight up and the reflector on the ground. Most of the time this will produce acceptable results when mounted but there are variables that can mess this up too. If the antenna is vertical, you'll need the mast in place to tune it also.
 
his method of rescaling is the exact method you would use to rescale any antenna for any band.it's not rocket science.

although generally speaking if rebuilding an antenna from scratch for another band,
you should rescale every single dimension of the antenna including element diameters,in this case your stuck with certain diameters and rescaling distance between element spacing might not be so easy,

just changing the element lengths alone should get you pretty much in the ballpark as 27.555 isn't a million miles from 27.205. as you can see from Lorenzo's calculation the new sizing is almost 99% (98.71% to be precise) of the original size.

on another note the ros meter Lorenzo refers too is an ordinary swr meter,ros = rapport d'onde stationnaire or "ratio wave standing" from the french language.
 
Dear Mr. robb

(hehehehe)

no need to buy a metric tape measure . just use one of the many conversion charts on the WWW . most tapes will measure to 1/16 of an inch , some will go to 1/32 .
 
BOOTY MONSTER said:
Dear Mr. robb

(hehehehe)

no need to buy a metric tape measure . just use one of the many conversion charts on the WWW . most tapes will measure to 1/16 of an inch , some will go to 1/32 .
Click to expand...

That's what I did when constructing my lw-150 and check vertical element and screw length, just haul the old laptop out and set it on the tailgate of the pickup hehehehe.
 
momma used to say ......
if everybody else jumps off a cliff ................
:)
 
Just lay out a quick sketch with the converted dimensions, or take the original drawing with metric dimensions and add the converted dimension in parentheses. You could even make a copy of the original, white out the metric dimensions and add the coverted dimensions to it. It's done this way in machine shops and fab shops all over the country.

Anyway, that's what I would do.
 
jazzsinger said:
his method of rescaling is the exact method you would use to rescale any antenna for any band.it's not rocket science.
Click to expand...

Jazzsinger, you do have a point. it is commen antenna knowledge.
Shockwave is always quite enthousiastic about sirio (nothing wrong ment with that though)
im sure he is very enthousiastic about other things aswell.

Attached you can find the different eznec diagrams of the antenna at 27,5 Mhz.
There is over a dB "loss" if one does not change the element spacings.
But only element length.

If one doesnt change the element spacing but only the element length
The entire antenna becomes too high in frequency.
The best gain and FB would be around 28 Mhz and so is its resonant frequency.
(with only the different element sizes)
The impedance drops to about 18 Ohms at 28 Mhz. At 27,5 a reactance comes into the game and optimum performance cant be expedted.
Ofcourse it would be possible to match the antenna but in that case it is again a beautifull antenna with a beautifull SWR but with less than optimum Gain and FB figures.

Im not sure if it is easy to change the element spacing or not of that antenna.
If not, a answer from Sirio refering to the original spacings and only (optimal)different element lengths would be more appropiate, as im sure one is able to get 7,5 dBI around 25 dB FB and a resonant frequency of 27,555 without changing the spacing.
Perhaps specific question towards them will give a answer.
Otherwise there are quite a few on this forum who could model it.

Element diameter in this case doesnt effect the antenna in a way one can notice.
It will be difficult to measure if that is possible at all.

Kind regards,

Henry
11 meter Dx antenna systemx
 

Attachments

  • sirio SY4 Rescale.doc
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