RE>rfi-digest V1 #70 5/22/98
Bob Wanderer wrote in issue V1 #70:
>>From: Bob Wanderer <aa0cy@nwrain.com>
>>Subject: RE: [RFI] Spurious signal levels
>> When I had a spurious problem on 14 MHz
>> back in the late 70's, I called the FCC
>> Laurel, Md. Lab) to find out whether the
>> measurement was into a dummy load or into
>> the antenna itself (as the levels were
>> different and into the dummy load less
>> than the limits discussed below). They
>> couldn't answer. I eventually was able to
>> solve the problem (brought SWR from 3:1 to
>> 1.7:1 by modifying the angle of the radials
>> on the trapped 1/4-wave vertical). I lost a
>> bit of respoect for the Commission's
>> technical representatives. Anyway, what's
>> the answer?
>> 73, Bob AA0CY
The FCC measures transmitter spurious products at the output with the
transmitter operating into its designed load.
However... our responibility, IMO, is to _radiate_ signals whose spurious
products meet the requirements.
For type-acceptance/certifcation, the FCC would usually use 50 ohm ports, but
for determining our compliance with the Rules, they'd use a spectrum analyzer
or receiver, and an antenna. This makes the transmitter output impedance
irrelevant.
The requirements may READ the same, but they're different measuremnts.
(This raises another question; many spectrum anaylzers have a dynamic range
insufficient to detect low-level spurious signals in teh presence of other,
strong signals -- but that's the FCC"s problem, and maybe someone's defence!)
Cortland Richmond, KA5S
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