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

[Björn]

I agree with Tim.  

Adding to that - if someone pitches a *surveying* antenna - antenna calibration data must be easily found on a “well known” antenna calibration database. Or at least supplied by the manufacturer in a meaningful format.

https://www.ngs.noaa.gov/GRD/GPS/DOC/page4/antcal.html

http://www.geopp.com/pdf/gppigs06_pabs_g.pdf

/Björn 

Sent from my iPhone

> On 14 Nov 2020, at 08:12, Tim S <tim.strommen at gmail.com> wrote:
> 
> 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
>>>> 
>> 
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