My recent experience certainly hasn't been the same.
The FCC seems to have become quite arbitrary.
Example 1. cellular base station emissions are supposed to be -65dBc at a
specified frequency delta. They are well in excess of that, but the
emissions are still strong enough to affect an adjacent carriers' base
station receive. FCC says fix the transmitter (more filtering).
Example 2. FM broadcast station has an 8th harmonic strong enough to
disrupt call processing on a nearby cellular base station. But it meets
the BC spurious rules. FCC says, sorry, nothing we can do, it's compliant.
Anyone care to link these two answers with a single thread of logic?
>In the USA the bottom line regulation is we are not allowed
>to have any emission, no matter what level, that causes a
>problem.
>
>This is why Novices commonly received warnings or citations
>for out of band harmonics. If the FCC can hear it and
>decides it is a potential problem you are obligated to fix
>it even if it meets all test criteria. They also worked that
>way with BC stations. We had an FM station that was half the
>frequency of a local VHF TV channel's video carrier. Even
>though well over 100dB down on the second harmonic, we were
>obligated to shield and suppress until the problem went
>away.
>
>But it is true that the requirement is to only test into 50
>ohms.
>
>All that aside most class AB PA's with a reasonable tank
>layout and reasonable tank Q will have no problems meeting
>the minimum requirement under test conditions. As you point
>out (via the link) harmonics are all over the place
>depending how the tank is wired and how the components are
>mounted. One of the least important things are inductor's
>position with respect to the cabinet or chassis. Much more
>important is capacitor mounting (ground path impedance),
>lead routing from the tube to the capacitor, and how the
>output lead is taken out of the PA compartment. With a pi-L
>mutual coupling between the L coil and the early parts of
>the tank is very important.
>
>
>
>73 Tom
>
>
>
>
>
>
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Scott Townley NX7U
Gilbert, AZ DM43di
http://members.cox.net/nx7u
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