I've been sleuthing the FCC licenses for Southwest Airlines at Dulles Airport and have come up with that not a one of the licensed freqs are used.
However, closely watching the waterfall near 460.7625 (a freq licensed to Southwest) I found 460.7675 (a freq NOT licensed to Southwest, nor is it licensed to anyone anywhere) with activity and concluded that this was a DMR single freq system used by Southwest Airlines. But then I wondered about the narrowbanding in the UHF band which leads me to this question.
Is 460.7675 a correct frequency? My understanding is that there is 6.25 khz between freqs so 460.7675 would not be an allocated freq.
If I run out a list of frequencies starting with 460.000 at 6.25 khz intervals there is no 460.7675 in that list. The closest freq is 460.76875. Then I zoom in tight on the SDR waterfall and lo and behold it looks like the center freq is 460.76875.
What fooled me initially was that I was receiving voice and data (Cap+, Color Code 12) on the SDR (DSD+) and the SDS100 on freq 460.7675. And I receive the same on 460.76875, which I am lead to believe is the correct frequency.
The odd thing of all of this is the Southwest Airlines is not licensed for 460.7675 or 460.76875 at Dulles Airport. Nonetheless, Southwest Airlines is using 460.76875. How is it not shown in the FCC licenses? Beats me.
If someone else can chime in on this subject I'm all ears.
However, closely watching the waterfall near 460.7625 (a freq licensed to Southwest) I found 460.7675 (a freq NOT licensed to Southwest, nor is it licensed to anyone anywhere) with activity and concluded that this was a DMR single freq system used by Southwest Airlines. But then I wondered about the narrowbanding in the UHF band which leads me to this question.
Is 460.7675 a correct frequency? My understanding is that there is 6.25 khz between freqs so 460.7675 would not be an allocated freq.
If I run out a list of frequencies starting with 460.000 at 6.25 khz intervals there is no 460.7675 in that list. The closest freq is 460.76875. Then I zoom in tight on the SDR waterfall and lo and behold it looks like the center freq is 460.76875.
What fooled me initially was that I was receiving voice and data (Cap+, Color Code 12) on the SDR (DSD+) and the SDS100 on freq 460.7675. And I receive the same on 460.76875, which I am lead to believe is the correct frequency.
The odd thing of all of this is the Southwest Airlines is not licensed for 460.7675 or 460.76875 at Dulles Airport. Nonetheless, Southwest Airlines is using 460.76875. How is it not shown in the FCC licenses? Beats me.
If someone else can chime in on this subject I'm all ears.