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..."
