[amsat-bb] Re: External Amplifier Legality Questions

Paul Stoetzer n8hm at arrl.net
Wed Mar 19 12:14:26 PDT 2014

Hi Zach,

What is the power output you have available from your transceiver and
what type of antennas/coax do you plan to use.

In most cases, you need no more than 100W EIRP to operate through any
LEO satellite. There are some rare exceptions where you might go a
little beyond 100W EIRP, of course, but if you have a transceiver
capable of putting out 20 watts and are feeding a moderate sized yagi
with high-quality coax, you almost certainly don't need an amplifier.

You are correct that you may use that amplifier filtered as described,
but depending on your situation, it may be best to put your money
towards antennas and coax.


Paul, N8HM

On Wed, Mar 19, 2014 at 2:18 PM, Zach Leffke <zleffke at vt.edu> wrote:
> 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.
> Sincerely,
> Zach, KJ4QLP
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