FCC Part 97.307(d)
"For transmitters installed after January 1, 2003, the mean power of any
spurious emission from a station transmitter or external RF amplifier
transmitting on a frequency below 30 MHz must be at least _43 dB below
the mean power of the fundamental emission_. For transmissions installed
on or before January 1, 2003, the mean power of any spurious emission
from a station transmitter or external RF power amplifier transmitting
on a frequency below 30 MHz must not exceed 50 mW and must be at least
40 dB below the mean power of the fundamental emission. For a
transmitter of mean power less than 5W installed on or before January 1,
2003, the attenuation must be at least 30 dB . A transmitter built
before April 15, 1977, or first marketed before January 1, 1978, is
exempt from this requirement."
Fortunately most manufacturers exceed the 43 dB number by a significant
amount. By the way 43 dB below 1500W is 75mW.
73,
Larry, W0QE
Robert Groh wrote:
> Oh, boy, all kinds of questions to ask here.
>
> First off - how is he detecting these harmonics? It would be very easy to
> overload the detecting device and have the harmonic being produced inside the
> detecting device (e.g. receiver). Trying to measure harmonic content in close
> proximity to the transmitter/PA is difficult in a non-lab environment. Using
> a buddy a couple of miles away would be quite acceptable (if you know the
> relative antenna gains, etc).
>
> Second - every practical amplifier will have harmonic content. My mind is
> rusty on what the current FCC requirements are but I believe it is somewhere
> south of 60 dB down from the output. If he is putting out 1 KW means the
> harmonic(s) could be as high as 1 mW (i.e. +30 dBw out - 60 dB = -30 dBw = 0
> dBm) and be entirely within specification. 1 mW is a lot of power!
>
> Third - his antenna will undoubtedly have some (probably substantial)
> rejection to the 3rd harmonic. So the 'radiated' 3rd harmonic will be knocked
> down even more.
>
> Fourth - if he is actually causing interference on the 3rd harmonic and it is
> not interference caused by close proximity then I would simply recommend he
> consider a simple low pass filter in his feed line (e.g. with a 3 MHz
> cutoff). Should be fairly easy to build and would give > 15 dB attenuation.
>
> Hope this all helps in a general sense.
>
> 73
> Bob Groh, WA2CKY
>
>
>
>
> ________________________________
> From: gds <gerys1@verizon.net>
> To: amps@contesting.com
> Sent: Sat, January 30, 2010 9:51:19 PM
> Subject: [Amps] Advice: harmonics from Alpha 91B on 160
>
>
> A friend of mine is using an Alpha 91B on 160 and is noticing harmonics
> around 5.595 MHz. (3rd order)
>
> Is this a problem that has been noticed with the 91B? Anyone know of a
> solution?
>
> Tks very much.
>
> Gerry
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|