[TenTec] RF Speech Processor "TX IMD"

Al Gulseth wb5jnc at centurytel.net
Sun Jun 16 19:50:23 EDT 2013


97.307 doesn't specify which order IMD or what testing method; paragraph (d) 
just says "spurious emissions" must be at least 43 dB below fundamental (2003 
on, pre-1978 products are exempt.) I interpret this to be a "catch-all" 
covering IMD, harmonics, and all other forms of undesirable by-products in 
the signal, under any operating conditions.  However, the "kicker" for me is 
in paragraph (c):

 (c) 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.

especially the "If _any_ [emphasis added] spurious emission... causes harmful 
interference to the reception of another radio station" part. That to me says 
that the radios you refer to are in violation of the "spirit" if not the 
letter of the law, although (wrongly in the case of the radios we are 
discussing IMHO) the FCC puts the responsibility for correcting the issue on 
the licensee instead of the equipment manufacturer.

Here's a link to 97.307 on W8JI's web site if you want to read it for 

73, Al

On Sun June 16 2013 3:24:37 pm Rick - DJ0IP / NJ0IP wrote:
> It is inadequate, Al.
> There are lots of transceivers that create a very broadband noise.
> The noise is adequately suppressed to meet the legal specs, but if you hang
> an amp on them, a neighbor a mile away might have problems.
> A next door neighbor will have problems every time that radio transmits,
> regardless of what band it is on.
> Yet it passes the specs.
> I am not aware of the details of 97.307;  does it specify just 3rd order
> IMD or does it specify more?
> Does it just specify 2-tone testing?
> In the meantime Rob is testing using white noise in addition to the 2-tone
> tests.
> This more closely resembles speech.
> Part of the problem is, some of the modern radios have really bad 5th, 7th,
> 9th (etc.) order IMD and even farther out.
> One of Rob's presentations was quite long.  I was unable to upload the
> Audio file (too large) so I split the presentation into 3 parts, with
> "Transmitters" being one of the 3.
> Anyone interested in more info on this theme should look at his
> presentation and listen to Rob in the audio file.
> The presentation was his 2011 BARC presentation, entitled "Transceiver
> Performance; What's new in 2011?"
> Here is a link to the presentation and 3 audio files which accompany it:
> http://www.dj0ip.de/transceivers/sherwood/barc-new-in-2011/
> The middle presentation, slides 24-43 address the transmitter issues.
> 73
> Rick, DJ0IP
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Al Gulseth
> Sent: Sunday, June 16, 2013 8:52 PM
> To: tentec at contesting.com
> Cc: Richards
> Subject: Re: [TenTec] RF Speech Processor "TX IMD"
> Actually, there is already a government mandated "clean transmitter
> standard."
> It's called "Sec.  97.307" (as in FCC Part 97) and is titled "Emission
> standards." Might an update of this section of Part 97 to address the
> issues raised in this discussion perhaps be in order?
> Although, the "spirit" of 97.307 already addresses several of the items you
> mention: concerning "a limit on bandwidth," note, for example, that it says
>    (a) No amateur station transmission shall occupy more bandwidth than
>    necessary for the information rate and emission type being transmitted,
> in
>    accordance with good amateur practice.
> My reading of this section would seem to indicate a mandate for "clean,
> narrow banded signals with minimal splatter" is there already. While
> needless to say improper equipment design is responsible for some of the
> "garbage" on the bands, many more of the poor on-air signals we hear are
> due to misadjustment by the operator and/or simple failure to follow "good
> amateur practice."
> 73, Al

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