Satellite Communications/Cross pol test
I have some problems when I want to take the crosspol test
with Intelsat 14 C-band.
Intelsat 14 gave us two frequencies to take the crosspol test
The first frequency is in the low range of frequency and the maximun crosspol I had is 23 dB of isolation.
But when I used the second frequency that is inthe higher range of frequency the crosspol that I had is 28 dB of isoltaion.
what is differents frequencies the crosspol has the variation?
The 2 frequencies are in differents transponder
Im looking forward for your answer
Have I nice day
You indicated that you have taken two cross-polarization measurements at C-Band on Intelsat 14. One of the measurements was at the low frequency edge of the band and the other was at the high frequency edge of the band. Each of the two measurements was made on a different transponder.
Much of the following material comes from the Engineering Statement provided by PanAmSat Licensee Corp. (“PanAmSat”) to the U.S. Federal Communications Commission (“FCC”).
Intelsat 14 is located at 45-degrees west longitude is operated by PanAmSat. Intelsat 14 is a Space System Loral model LS-1300 spacecraft that operates on the C-band frequencies 5925 – 6425 MHz, 3700 – 4200 MHz, and Ku-band frequencies 14000 – 14500 MHz, 11450 – 11950 MHz. The spacecraft utilizes 40 C-band channels and 22 Ku-band channels to provide service to Europe, Africa, South America, Central America, the Caribbean and portions of the Continental United States.
The Engineering Statement notes on page 10:
“Specifically, with the exception of the left hand and right hand circularly polarized C-band Europe-Africa receive beams and the hand circularly polarized C-band Europe-Africa transmit beam, the ratio of the on-axis co-polar gain to cross-polar gain (i.e., the cross-polarization isolation) is less than 30 dB over a limited portion of the primary coverage area of the remaining C-band receive and transmit beams and less than 30 dB over a limited portion of the primary coverage area of the Ku-band receive and transmit beams. Accordingly, PanAmSat requests a waiver of Section 25.210(i) of the [Federal Communications] Commission’s rules with regard to these beams.
“For those Intelsat 14 beams that do not meet the cross-polarization requirement of Section 25.210(i), the cross-polarization isolation is equal or greater than 20 dB. The level of cross-polarization isolation for non-compliant beams was the best that the satellite manufacturer could achieve without causing excessive degradations in the co-polarized gain of the beam and/or in the size of its coverage area.”
It appears based upon the above Engineering Statement that your cross-polarization isolation measurements are in the right ballpark, between 20 and 30 dB.
To provide a more conclusive answer, I would have to know the frequencies at which you made your measurements, and then I would have to map them back to specific transponders. However, there is no reason to expect the two measurements to be identical. Each transponder has its own filters and there are filter-to-filter variations.
My experience in manufacturing RF equipment demonstrates that each transponder typically requires SIT (“select-in-test”) components and a considerable amount of adjustment to achieve the specified performance metric. That problem is quite apparent in PanAmSat’s Engineering Statement.
If you want the Engineering Statement, I suggest that you Goggle “PanAmSat Engineering Statement for Intelsat-14.”
I hope that this helps you. I apologize for the delay. My wife had surgery early Thursday morning. Although not serious, I clearly was preoccupied.
I would appreciate it if you would rate my response if you like it. If you do not like it, please get back to me to resolve any concerns.
Thomas E. Burke, PhD, PMP