[Elecraft] Spurs on 15m from new laptop

[Kevin Cozens]

On 12-05-15 10:46 AM, VE3GNO Daniel wrote:
> I am wondering how they get FCC certification? I would advise to return
> it back due compliance issue..my 2 cents

Some years back I was working for a company that had an RF based hand-held 
real-time data collection system used in focus groups. The hand-held devices 
and the base station both had type approval for use in Canada and the US. 
After using the devices for a few years the company wanted to use the 
devices in the UK so the units were submitted for UK type approval.

Both base station and hand-held failed the approval process.

The hand-held transmitted in the 49MHz band using a 16.6xx MHz crystal 
running in third overtone (ie. 16.6xx times 3 = ~49MHz). It failed because 
of emissions exceeding allowed limits for the 900MHz(!) band.

As soon as I connected the spectrum analyzer I saw spurs every 16.6xx MHz in 
to the GHz range. The person that designed it must never have used an SA or 
they shouldn't have let it get past the prototype stage. Fortunately I found 
a simple solution. I changed the 7404 used in the crystal oscillator with a 
74U04 (unbuffered) and all the spurs dropped in strength from being equal to 
the fundamental to barely measurable. The hand-held passed on the second 
submission for UK approval.

This made me realize that FCC type approval doesn't mean a lot as a unit can 
still put out a lot of of unwanted RF emissions and simple circuit changes 
can often clean up a design if someone cares at all. The FCC type approval 
process is nowhere near as strict as it should be but it is still better 
than not having an approval process at all.

The one noise source I have at home is the high efficiency furnace that 
creates a tremendous amount of broadband RF noise when it goes in to a 
heating cycle during the winter months. I'm sure it was type approved too. :-P

-- 
Cheers!

Kevin.

http://www.ve3syb.ca/           |"Nerds make the shiny things that distract
Owner of Elecraft K2 #2172      | the mouth-breathers, and that's why we're
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