[amsat-bb] Re: External Amplifier Legality Questions

Kevin Muenzler, WB5RUE kevin at eaglecreekobservatory.org
Wed Mar 19 13:12:42 PDT 2014

Amateur radio equipment does not have to be FCC type accepted but it must
meet the requirements of Part 97.  So you may repurpose your commercial amp
for ham radio use as long as it meets the requirements of a "clean signal"
and does not violate the power limitations of your license or the band.

Kevin Muenzler, WB5RUE
Eagle Creek Observatory
I'd be unstoppable if it weren't for law enforcement and physics

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Zach Leffke
Sent: Wednesday, March 19, 2014 1:19 PM
To: amsat-bb at amsat.org
Subject: [amsat-bb] External Amplifier Legality Questions

Hello everyone,
     I have a question about FCC Rules regarding external amplifiers.  I am
considering re-purposing a wideband commercial amplifier for amateur use as
a final stage for my ground station. The amplifier is capable of producing
about 100W of power between 20 MHz and 500 MHz.  I want to use this amp in
conjunction with coax relays to switch between the 2m band and the 70cm band
depending upon which spacecraft I'm operating.

My questions are as follows:
Is it legal to use an amplifier designed for commercial applications in the
Amateur Bands?  This amplifier does not meet spurious signal suppression
requirements, so I plan to use band specific filters after the amp to make
sure I knock any spurs down below the required limits.  
Does the amplifier have to be type certified for use in the amateur bands?

As far as I can tell reading Part 97.315(subsection 3), The amplifier itself
does not need to be type certified if:
"(3)The amplifier is sold to an amateur radio operator or to a dealer, the
amplifier is purchased in used condition by a dealer, /or the amplifier is
sold to an amateur radio operator for use at that operator's station/.
[emphasis added]"

I'm planning to use it in my amateur station so I don't think it has to be
type certified.  Am I missing something?

Also, The amplifier's 2nd Harmonic is about -30dBc down at 145 MHz. 
According to 97.307e:
"The mean power of any spurious emission from a station transmitter or
external RF power amplifier transmitting on a frequency between 30--225 MHz
must be at least 60 dB below the mean power of the fundamental."

I'm planning to use a filter with about 40 dB of suppression at 290 MHz (2nd
harmonic), so I get about -70 dB of suppression at the second harmonic,
meeting the emission requirements of 97.307e.

I see no specific spurious signal suppression requirement for the 70cm band.
The amplifier has similar 2nd Harmonic characteristics and I'm planning to
use a similar filter for the 70cm band so the spurs should be down by about
70 dB of the fundamental mean power as well.  The only wording I see that
might apply is 97.307c:
"All spurious emissions from a station transmitter must be reduced to the
greatest extent practicable. If any spurious emission, including chassis or
power line radiation, causes harmful interference to the reception of
another radio station, the licensee of the interfering amateur station is
required to take steps to eliminate the interference, in accordance with
good engineering practice. "

I'm taking steps to eliminate interference by suppressing the 2nd Harmonic
down about 70dB from the fundamental "in good engineering practice" so I
think I meet all the requirements.  Again, what am I missing?

I've heard of lots of hams re-purposing amplifiers for amateur use without
legal concern, and I think this might be the case for my 
situation.   I'd like some advice from those that may have gone down 
this road in the past.  Any and all feedback from the group on this would be
greatly appreciated.  If I'm way off, please let me know.

Thanks in advance.

Zach, KJ4QLP

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