[amsat-bb] Re: External Amplifier Legality Questions

Rich/wa4bue richard.siff at verizon.net
Wed Mar 19 12:10:44 PDT 2014


Seems you have the regs down well.

You modify it is like Home Brew, still must meet to meet FCC specifications.

The question is why do you need that much pwer for the satellittes?

You should keep your power down to a minim to communicate so you don't 
stress the birds.

100 watts with a 10dB gain is a lot of ERP!


----- Original Message ----- 
From: "Zach Leffke" <zleffke at vt.edu>
To: <amsat-bb at amsat.org>
Sent: Wednesday, March 19, 2014 2:18 PM
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.
> Sincerely,
> Zach, KJ4QLP
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