[time-nuts] Procom GPS4 quadrifilar antenna...

David Kirkby david.kirkby at onetel.net
Fri Jun 8 21:31:15 UTC 2012


On 8 June 2012 13:20, Michael Baker <mpb45 at clanbaker.org> wrote:
> Time-nutters--
>
> The Procom website lists the noise-figure of their quadrifilar
> LNA as:
>
> GAIN > 30 dB
> NOISE FIGURE < 3 dB (incl. input filter).
> Typ. approx. 3 dB
> ------------------------------------------------------------
>
> I am a little surprised at this relatively high NF for a
> product in this price category.  Even most low-end
> mass-produced consumer grade GPS antennas are
> spec'd at 1.5 to 2.0 dB NF.
>
> Mike Baker

I know at least in antennas, consumer and at low/mid end professional
products rarely meet their specs.Even SWR, which is fairly easy to
measure is often not met on antnenas. Gain is never measured  - the
figures are just made up.  It seems everyone lies, and needs to lie to
remain in business. Just look on eBay and see some of the redicusly
high gains for some antennas, where the sellers has a feedback of
10000 and 99.9% positive. Of course, for radio hams, dramatic lies
about the SWR would be detected, but gain figures are unlikely to be
challenged.

That said, I don't undeerstand how something can have a spec of < 3dB
NF, then have a typical noise figure of approximately 3 dB. But I bet
a lot of manufactures of GPS antennas have the NF of their device
being that of the amplifier chip they use, and all losses, like those
of filtering, are ignored.

Dave




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