[time-nuts] L1/L2 survey antenna $125 new

[Tim S]

I'd doubt it's a choke-plate design - too small, and it looks like
other Cheap dual-element designs I've seen come out of China.  I don't
agree with sparkfun's recommendation of using the cheapest Chinese adapters
you can buy to get a decent SWR/insertion-loss.

What's notably missing in the datasheet besides a clean translation - is
data and specifications.

Frequency range is quoted as "GPS L1/L1 + GLONASS L1/L2" rather than
actually giving a numerical frequency range.  There is also the statement:
"...equipped with anti-multi-path choke plate, with anti-surge design, can
effectively suppress the out-of-band strong interference signal to ensure
the reliability of the antenna..."

As someone who has occasion to wade through Chinese sales pitches for
sneaking their way into well known product families through untrained
corporate buyers, this appears to be what I will coin the phrase "pseudo
keyword soup".  There's just enough somewhat familiar key-word sounding
terms in that sentence to suggest:
1) that this is a choke ring, not a "ground plane independent antenna"
(what it appears they have actually designed)
2) that it has surge suppression, and that surge suppression is acting as
an adjacent band filter (I seriously doubt that)

* If it was a choke ring, I expect to see an elevation number for
multi-path rejection, as well as plots - and horizontal dimensions
(diameter) >10" for single L1 and >12" for dual band L1/L2.
* If it has surge suppression, I'd expect to see what surge model they were
suppressing
* If it had out of band filtering, I'd expect to see cutoffs and dB
numbers...

Those bullets above would be features a savvy GPS antenna buyer would be
looking for, and it's easy to forget to read and verify the performance
numbers are actually "good".

As an example, this antenna (
https://www.tallysman.com/product/tw3882-dual-band-gnss-antenna/) from a
Canadian company has about the same keyword-soup equivalent terms, except
the specs are, for lack of a better term IMHO "more reputable" and
verifiable.  I picked up a few of these a few months back for the car
tracking project, with white colored radomes and Type-N male bulkhead
connector mounts - about $300/each.

Notable, they have a typical antenna axial ratio 1/3 of the Sparkfun
antenna, with a max value of 1/2 the Sparkfun part (and it is called out as
flat across the whole band), have 5db less of LNA amplification - but at
half the current draw (and specifically the LNA performance is invariant
from 2.5-16VDC), and specifically the ESD is rated for 15kV of air
discharge - the VSWR is better, and they have actual out of band rejection
numbers (with good minimum rejection of >30dB, many comon radio types like
cellular are >40dB rejection) - and they give the specific bandwidth of
each band.  It is however not ground plane independent (but my use is
vehicular, so not a problem) - but without the ground plane, it's less than
half the size of the Sparkfun part, and the recommended non-roof ground
plane is 100mm (~2" smaller diameter than the Sparkfun part).

You get what you pay for IMHO - while interesting, the Sparkfun part comes
across as a puppy trying to get away with playing with wolves, and hoping
the other wolves don't notice it's food.  Your mileage may vary though.

-Tim S


On Fri, Nov 13, 2020 at 7:56 PM <time-nuts-request at lists.febo.com> wrote:

> From: Robert LaJeunesse <lajeunesse at mail.com>
> To: time-nuts at lists.febo.com
> Subject: Re: [time-nuts] L1/L2 survey antenna $125 new
> Message-ID:
>
> <trinity-ef99ff3c-a78e-44a5-8ab9-c357610d106c-1605321572235 at 3c-app-mailcom-lxa15
> >
>
> Content-Type: text/plain; charset=UTF-8
>
> Dana, no plans to buy. Just put up my L1 antenna last weekend.
>
> Bob L.
>
> > Sent: Friday, November 13, 2020 at 7:26 PM
> > From: "Dana Whitlow" <k8yumdoober at gmail.com>
> > To: "Discussion of precise time and frequency measurement" <
> time-nuts at lists.febo.com>
> > Subject: Re: [time-nuts] L1/L2 survey antenna $125 new
> >
> > I quote the description on the SparKfun page via the WIndows clipboard:
> >
> > "Note: This antenna has a TNC Male RP connector found on nearly all
> > surveying antennas. We recommend a TNC Male RP to SMA adapter
> > <
> https://www.amazon.com/DGZZI-2-Pack-Coaxial-Adapter-Connector/dp/B06ZZGGWBS
> >
> > or
> > cable when using with our GNSS receivers."
> >
> > But the photo on the site appears to show a receptacle, not a pin, for
> the
> > center conductor, hence
> > a standard female configuration.  So unless the thread is left-handed,
> > which I really can't tell,
> > this is a standard (not RP)* female* connector.  That's my story and I'm
> > sticking to it!
> >
> > Bob, are you by chance thinking of buying one of these?  If so, please
> let
> > us know which it
> > is right away when it arrives.
> >
> > Dana
> >
> >
> > On Fri, Nov 13, 2020 at 1:34 PM Robert LaJeunesse <lajeunesse at mail.com>
> > wrote:
> >
> > > Just spotted this: https://www.sparkfun.com/products/17382
> > >
> > > Datasheet:
> > >
> https://cdn.sparkfun.com/assets/6/e/a/9/2/BT-147_GNSS_Antenna_Datasheet.pdf
> > >
> > > Chokeplate design, 40dB LNA, TNC connector
> > >
>