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need info on how to modify a sirio sy27-4 for 10m
- Thread starter eacky
- Start date
Very basically, you adjust the lengths of the various elements to the higher frequency. that means that presently the elements are too long. So, you 'scale' the antenna to the frequency you want.
One method is to measure each element. Then multiply those measurements by the antenna's resonant frequency (where it's tuned for now). Then divide those numbers by the new frequency you want the thing to be resonant on. Convert those feet and inches to a decimal number (18 feet and 3 inches would then be 18.25 feet). Then divide that number by the frequency. Keep the frequency in the same measurements too. Channel 19 is 27.185 Mhz, so the new frequency should be in Mhz too.
That should get you in the ball-park, and then using the gamma match to do the impedance matching just like you did for 11 meters.
- 'Doc
One method is to measure each element. Then multiply those measurements by the antenna's resonant frequency (where it's tuned for now). Then divide those numbers by the new frequency you want the thing to be resonant on. Convert those feet and inches to a decimal number (18 feet and 3 inches would then be 18.25 feet). Then divide that number by the frequency. Keep the frequency in the same measurements too. Channel 19 is 27.185 Mhz, so the new frequency should be in Mhz too.
That should get you in the ball-park, and then using the gamma match to do the impedance matching just like you did for 11 meters.
- 'Doc
Here you go:
Method #1
*Buy antenna
*Assemble
*Tune Gamma match for ~27.555mhz
*Use antenna tuner to get 10m
*That is one way - but it does work
OR
Method #2
Go through the painstaking process of trimming each element length by dividing 27.205mHz (stock tuning for this beam) with the frequency center that you want to tune it to - say 28.400mHz phone band. I get ~0.957922; this is what you use as a multiplier for each element length. The spacing between the elements will also need to be shifted by that same multiplier.
But I use method #1.
Although it might not be the best/proper way and it will change the lobe pattern somewhat, it works without much fuss.
SY27-4,
Method #1
*Buy antenna
*Assemble
*Tune Gamma match for ~27.555mhz
*Use antenna tuner to get 10m
*That is one way - but it does work
OR
Method #2
Go through the painstaking process of trimming each element length by dividing 27.205mHz (stock tuning for this beam) with the frequency center that you want to tune it to - say 28.400mHz phone band. I get ~0.957922; this is what you use as a multiplier for each element length. The spacing between the elements will also need to be shifted by that same multiplier.
But I use method #1.
Although it might not be the best/proper way and it will change the lobe pattern somewhat, it works without much fuss.
SY27-4,
Last edited:
The only problem I see with using standard beam dimensions with the Sirio beam, is that the Sirio beam doesn't use a standard length boom. The boom length on the Sirio is about~13 ft long; whereas the standard boom is about~16 ft for a 4 element Yagi.
Soooo . . . . Having said that, the way to change the beam for 10m is to scale it using the formula above for the element and spacing between the elements. That should work out OK.
This Sirio beam beam was 'computer optimized'. Which I suspect means that some engineers at Sirio used some EZNEC program to make it work on a short boom length. This part is speculation; but if you must you might try to contact Sirio and ask for the details. If you must. I did.
That is the same info the Mr Mezzadrelli sent me concerning re-tuning the beam for a different freq center. But I would double check my math to be sure that it is correct before you commit to cut or change anything.
Ing. Mezzadrelli Lorenzo
SIRIO Antenne SRL
Via Liguria 15
46049 Volta Mantovana (MN) - ITALY
Ph. +39-0376-801515; fax +39-0376-801254
l.mezzadrelli@sirioantenne.it
Sirio Antenne - High Performance Antenna
Soooo . . . . Having said that, the way to change the beam for 10m is to scale it using the formula above for the element and spacing between the elements. That should work out OK.
This Sirio beam beam was 'computer optimized'. Which I suspect means that some engineers at Sirio used some EZNEC program to make it work on a short boom length. This part is speculation; but if you must you might try to contact Sirio and ask for the details. If you must. I did.
That is the same info the Mr Mezzadrelli sent me concerning re-tuning the beam for a different freq center. But I would double check my math to be sure that it is correct before you commit to cut or change anything.
Ing. Mezzadrelli Lorenzo
SIRIO Antenne SRL
Via Liguria 15
46049 Volta Mantovana (MN) - ITALY
Ph. +39-0376-801515; fax +39-0376-801254
l.mezzadrelli@sirioantenne.it
Sirio Antenne - High Performance Antenna
"Pains taking measurements"? Guess that just depends on how hard it is for someone to measure something. Other wise, that's about as 'standard'/'normal' a way of converting any antenna to a different frequency. Is it going to result in the absolute best optimized beam antenna for that new frequency? Nope, but it will certainly be adequate and typical.
Optimizing one particular aspect/characteristic of a directional antenna is always a compromise with it's other characteristics. If you want some of that 'optimizing', then go get it. That means using a tool that can tell you how to go about it, and that generally means an antenna modeling or 'optimizing' program. There's quite a few of them floating around (and for a long time) so finding one shouldn't be all that difficult.
- 'Doc
Optimizing one particular aspect/characteristic of a directional antenna is always a compromise with it's other characteristics. If you want some of that 'optimizing', then go get it. That means using a tool that can tell you how to go about it, and that generally means an antenna modeling or 'optimizing' program. There's quite a few of them floating around (and for a long time) so finding one shouldn't be all that difficult.
- 'Doc
I wouldn't be too concerned with element spacing but I would adjust the element lengths. The difference in spacing is not nearly as critical as the lenghs and will change the overall impedance more than it will change the pattern or gain as the difference in spacing from 11m to 10m is not that much as compared to the difference in element lengths. For single band use I would definitely adjust the lengths and forget about a tuner.
Thanks to all for the good info i will resize the elements and not bother with the spacing. I dont think the spacing will make to much of a difference, i'am new to ham radio and the internet. Got my ticket last month n' i've been a sw listener for about 15 years so i think i know a wee bit (not much) but its good to have the internet for info from people who know better thank guys. 73
Sent to me from Sirio/Italy:
Dear Mr. Xxxxxx:
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 lengths 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 doesn't work well; then you can also try to rescale the spacing
between elements (using the same formula above)
Reflector-driven: New length = 0.9871 x 1570 = 1550 mm
Driven-1 director: New length = 0.9871 x 1020 = 1007 mm
Director 1 - director 2: New length = 0.9871 x 1410 = 1392 mm
Then re-tune the antenna by 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
Engineer/Sirio
Dear Mr. Xxxxxx:
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 lengths 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 doesn't work well; then you can also try to rescale the spacing
between elements (using the same formula above)
Reflector-driven: New length = 0.9871 x 1570 = 1550 mm
Driven-1 director: New length = 0.9871 x 1020 = 1007 mm
Director 1 - director 2: New length = 0.9871 x 1410 = 1392 mm
Then re-tune the antenna by 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
Engineer/Sirio
Last edited:
Eacky, I wouldn't cut elements but instead just push then in, that way if you decide to go 11 meter or sell the antenna it will still work on 11 meter. Just a idea.
Yep. I'm not in any hurry to cut any elements for 10m. I'll construct the antenna to spec and then see how far from resonance it is. In a purely stupid move to increase gain, I may want to add another section or two of boom at a later date and add some directors, so the distance between the original Sirio mounting brackets on the factory boom might have to be lengthened.
Robb, I modeled the SY27 4 and I set its dimensions at about 27.205 (I split 27.555 / 27.000) but the antenna resonance shows up at 26.3 mhz. I'm pretty sure I did the math right. Even if I didn't I wonder why we see a difference in the measurements in the manual we posted here?
Then I checked your reference above in post #3 attachment and this page from your manual is different than the manual I checked on the Sirio Website.
Here is the page and the model I made to specs, and it sets up at 26.3 mhz like I noted above not 27.205 where I took the dimensions.
Then I checked your reference above in post #3 attachment and this page from your manual is different than the manual I checked on the Sirio Website.
Here is the page and the model I made to specs, and it sets up at 26.3 mhz like I noted above not 27.205 where I took the dimensions.