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.strom...@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-requ...@lists.febo.com> wrote: >> >> From: Robert LaJeunesse <lajeune...@mail.com> >> To: time-nuts@lists.febo.com >> Subject: Re: [time-nuts] L1/L2 survey antenna $125 new >> Message-ID: >> >> <trinity-ef99ff3c-a78e-44a5-8ab9-c357610d106c-1605321572235@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" <k8yumdoo...@gmail.com> >>> To: "Discussion of precise time and frequency measurement" < >> time-nuts@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 <lajeune...@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 >>>> >> > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.