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Sirio 3 ele yagi

SMILEX2692002

SMILEX2692002

Well-Known Member
Oct 26, 2011
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108
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Can someone explain what the specs below mean off the Sirio website regarding the 3 element yagi?

CB 27 MHz Base Antenna, SY 27-3 , SY 27-4


Bandwidth @ SWR ≤ 2:
SY 27-3: ≥ 1800 KHz

I might be wrong but does this mean the resonant frequency would be 27.205 and then the Swr would be at or below 2 untill -900 KHz in frequency or 26.305?
The same would apply to +900 Khz in frequency or 28.105.

If this is true could one adjust the gamma match so the resonant frequency is 27.600 and the -900 Khz in frequency would be 26.700 and on the other end the +900 KHz in frequency would be 28.500?

It would be really nice if it would work like that.
 

Lil'Yeshua said:
Typical SWR chart
Click to expand...

The chart dosent match up with the 1800 KHz bandwidth rating in the specs.
This chart shows a 1700 Khz swing in frequency from the left to right.
The chart shows the lowest swr at 27.170.

I still wonder if I adjusted the gama match for lowest SWR at 27.600 if it would work for what I want.

Could be fun to experiment with.
 
If you adjusted the gamma to be resonant at 27.6mhz it would work.

If you reconfigured the entire yagi dimensions for 27.6 mhz it would work better (More efficient).

468/27.6= 16.95 feet that is length of your driven element. ( where the gamma attaches)

Reflector will be 5% longer the driven element, director will be 5% smaller than the driven element.

Spacing of the elements will be fine as from the factory.

NOW adjust that gamma for your 27.6mhz yagi and have some fun.

The 3 element will give you more bandwidth and less gain than a four element yagi, but not that much less gain.



SMILEX2692002 said:
The chart dosent match up with the 1800 KHz bandwidth rating in the specs.
This chart shows a 1700 Khz swing in frequency from the left to right.
The chart shows the lowest swr at 27.170.

I still wonder if I adjusted the gama match for lowest SWR at 27.600 if it would work for what I want.

Could be fun to experiment with.
Click to expand...
 
Last edited:
wavrider said:
If you adjusted the gamma to be resonant at 27.6mhz it would work.

If you reconfigured the entire yagi dimensions for 27.6 mhz it would work better (More efficient).

468/27.6= 16.95 feet that is length of your driven element. ( where the gamma attaches)

Reflector will be 5% longer the driven element, director will be 5% smaller than the driven element.

Spacing of the elements will be fine as from the factory.

NOW adjust that gamma for your 27.6mhz yagi and have some fun.

The 3 element will give you more bandwidth and less gain than a four element yagi, but not that much less gain.
Click to expand...

Reflector 17.80 feet
Driven Element 16.95 feet
Director 16.1 feet
If I did the calculations correct.

Could this also be used with a Maco M103C 3 ele yagi?
Although the boom on the Sirio is 8.9 feet vs the M103c's 11.5 ft boom.
If I cut the M103c's boom to that of the Sirio and took the Sirio's element spacing here is what I come up with.
Space between the
Reflector to driven element is 4.72 feet
Space between the
Driven element to director is 4.07 feet
Seems like to much work to modify the Maco M103C though. Don't even know if it would work trying to scale it to the Sirio demensions listed above.
 
If you get either the Sirio 3 or 4 element beam, just put it together and don't worry about it. You can only put it together one way, as the mfr built it that way. When assembled, set the reflector on the ground and point the beam straight up twards the sky and adjust your SWR on Ch 20. Then, put it up on your mounting pole with your rotor - and have fun.

http://www.worldwidedx.com/cb-antennas/91374-sirio-sy27-4-beam-install.html
 
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You should also keep in mind that the graph is ->"typical"<- finds not exact or always guaranteed findings for that 2:1 SWR ratio bandwidth. A lot of things come into play with that and there's no way of predicting what each individual installation will be like. No manufacturer can guarantee you will have exactly they had when they tested their antenna unless you set the thing up -exactly- like they did when they did that testing. If you get 'close' you are doing about as good as can be expected. That 'close' thingy isn't always as 'close' as you might think or want...
- 'Doc
 
DO NOT change the diameters...distances etc.
It is most likely to have a negative effect unless you know what you are doing
(have done your modeling)

A example of the sirio sy4 can be found here:
Sirio SY 27-4
Dont worry about the swr graph ....it was set at 35 ohms where the antenna is 26 ohm.
The antenna his resonant point is at 27.4 Mhz
And it produces about about 8dBI (5,86 dBD) and 24 dB front to back.

The 4el maco will do about 0,7 dB more and has a 21 dB front to back at its resonant freq. (this case 27.0 Mhz)
And can be found here:
MACO_104C

There are options to futher improve the maco 4
As can be found here:
http://www.worldwidedx.com/cb-antennas/133137-4-element-yagi-specs-3.html

In aspect to provided bandwidth.
It is quite possible to provide a good indication regarding bandwidth.
Take for example: Dave 91dd018 (also on this forum and very well known in the cb community of course)
He constructed a 6el OWA the SWR is remarkble similair to the one provided by eznec.
6 el OWA Yagi | 91DD018

With that said...of course near by obstacles have influence, and so does the "type" of antenna (low impedance tends to be more critical)..
Or other things like rain/snow etc...But overall, you can have a very good indication.

And when done correctly you should be with int "tens" of Khz.
Comming from "experience" the 2:1 swr bandwidth is as predicted, but those "influences" can cause the antenna to "shift" a bit in freq.
Bare in mind ....it is not only SWR that is shifted !...so are all the other aspects of a yagi (gain/fr etc)
Now, you can "change" the swr with a gamma-match for example but you cant shift those other parameters with that gamma-match...
Dont forget that !

Actually all my antenna's are 50 ohms direct fed. IF the SWR curve wasnt as expected,
i wouldnt be in buisness anymore.

Kind regards,

Henry 19SD348
 
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Henry HPSD said:
DO NOT change the diameters...distances etc.
It is most likely to have a negative effect unless you know what you are doing
(have done your modeling)
Kind regards,
Henry 19SD348
Click to expand...

Henry, If I understand your reply correctly, you are say DO NOT make the antenna the electrical length for the target frequency? 27.6MHZ

Model it all you want, the laws of physics do not change.
 
I use the 4 element version on 10m, I reduced all elements by around 4" and left the spacing as original, although these are easy enough to adjust the boom is a little too short to benefit from a change in element spacing ;)
 
Yes, you migth not interpertating me correct waverider.
With that said...it then is probarbly me who explained things not good enough.

What im trying to say..

Exactly because of that `laws of physic`you just can not `copy` element lengths without changing the element distance AND element diameter as well.
All those three need to `combine`.

Of course one can make a `working` beam and with a matching system ...the SWR will be great.
But without a doubt your not pulling maximum from that beam.
Its easy to `loose` a dB (s) in gain and much much more on Front to back.

Thats the same as giving a indication that one shouldnt change element distance from 11 to 10 meters... Yes, for sure...some antenna models are quite forgiving.. (owa for example)
But anyone who has invested a bit of time in beams knows this is not the rigth way and can lead to very bad results..

The average CBer spends half of his time looking at that SWR needle and wants it "dead"...So why would he "agree" with a drop in in gain and probarbly many dB's in front to back ? Im sure he would like those to be "best" as possible.

The "oke" attitude is fine with me.......but it is not mine.

Kind regards,

Henry
 
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