[Amps] Advice: harmonics from Alpha 91B on 160

[Gary Schafer]

I suppose that 3rd order IM products could fall into the "spurious
emissions" category. There isn't a ham transmitter on the market that would
meet that.

73
Gary  K4FMX

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
> On Behalf Of Larry Benko
> Sent: Sunday, January 31, 2010 11:44 AM
> To: amps at contesting.com
> Subject: Re: [Amps] Advice: harmonics from Alpha 91B on 160
> 
> 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 at verizon.net>
> > To: amps at 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
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