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Measuring GPS antenna bandwidth

 

I am building a high accuracy RTK locating system to measure my property lines and the location of buildings on the property. To achieve centimeter accuracy, it uses signals from multiple locating satellite constellations on a range of frequencies between 1164 MHz and 1610 MHz including those used for American GPS. I have several GPS antennas, including a couple from high end Trimble survey systems but am unsure if their frequency response extends far enough beyond GPS frequencies and how flat the response is.

These antennas have built-in LNA's that utilize 3VDC supplied by receivers via the coax. The antennas and the LNA's need to be tested to ensure the system meets the bandwidth requirements. Some of them can be broken down to access the antenna & LNA separately but I'm unsure how to inject the necessary LNA DC power without impacting the nanoVNA measurements.

Does anyone have recommendations for testing antennas with built-in LNA's?

Regards,
George
 

You would have to buy or make a bias tee that works on that bandwidth. I
made one using stripline on a piece of G-10 pc board material. It was
designed for 1296 MHz. I don't know how well it will cover that bandwidth.
I only used it at 1296 MHz.

Zack W9SZ

On Thu, Jan 2, 2025 at 7:11?AM George via groups.io <forums=
[email protected]> wrote:

I am building a high accuracy RTK locating system to measure my property
lines and the location of buildings on the property. To achieve centimeter
accuracy, it uses signals from multiple locating satellite constellations
on a range of frequencies between 1164 MHz and 1610 MHz including those
used for American GPS. I have several GPS antennas, including a couple from
high end Trimble survey systems but am unsure if their frequency response
extends far enough beyond GPS frequencies and how flat the response is.

These antennas have built-in LNA's that utilize 3VDC supplied by receivers
via the coax. The antennas and the LNA's need to be tested to ensure the
system meets the bandwidth requirements. Some of them can be broken down to
access the antenna & LNA separately but I'm unsure how to inject the
necessary LNA DC power without impacting the nanoVNA measurements.

Does anyone have recommendations for testing antennas with built-in LNA's?

Regards,
George
 

You are going to find few GPS antennas that pick up both L1 and L2.The classic patch antenna does not have anywhere near the necessary bandwidth.Most of the antennas that do both really have 2 patch antennas in the design.
I test many antennas on my antenna range that have build in circuits.
First you need a DC Inserter.?? Mini-Circuits makes a nice little Inductor/capacitornetwork that does this. .??? Mount it on a PCB with a Connector to your antenna, anda connector to your test equipment.??? Does you VNA cover both GPS bands of interest?
So connect the GPS antenna to the Inserter, then the Inserter to your VNA.?? Add 3 volts of powerto the Inserter power line.
Connect the VNA to a broad band antenna that covers 1-2 GHz. point it at the GPS antennaand you should get a plot of the response.?

A signal generator and Spectrum Analyzer can also be used.
Good luck with your testing?? Kent WA5VJB

On Thursday, January 2, 2025 at 07:11:44 AM CST, George <forums@...> wrote:

I am building a high accuracy RTK locating system to measure my property lines and the location of buildings on the property. To achieve centimeter accuracy, it uses signals from multiple locating satellite constellations on a range of frequencies between 1164 MHz and 1610 MHz including those used for American GPS. I have several GPS antennas, including a couple from high end Trimble survey systems but am unsure if their frequency response extends far enough beyond GPS frequencies and how flat the response is.

These antennas have built-in LNA's that utilize 3VDC supplied by receivers via the coax. The antennas and the LNA's need to be tested to ensure the system meets the bandwidth requirements. Some of them can be broken down to access the antenna & LNA separately but I'm unsure how to inject the necessary LNA? DC power without impacting the nanoVNA measurements.

Does anyone have recommendations for testing antennas with built-in LNA's?

Regards,
George
 

Take a look at a RF/DC bias tee
 

Those look really good. The ZABT-2R15G+is on the expensive side but is
available from Mini-Circuits in quantities of one. The TCBT-6G+ and TCBT-14+are
less expensive but are only available from Mini-Circuits in a minimum order
of 10 each. Other models are also a lot more expensive. However, all of
these are available in single quantities from Mouser and all but the
ZABT-2R15G also available from Digi-Key.

Zack W9SZ

<>
Virus-free.www.avg.com
<>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

On Thu, Jan 2, 2025 at 10:43?AM Jim via groups.io <teotwaki=
[email protected]> wrote:

Take a look at a RF/DC bias tee
 

Hi George, Look up "Bias Tee Power Injectors" on Amazon.Lots of them
at $15 or so with stated bandwidth to 6GHz.

-----------------------------------------From: "George"
To: [email protected]
Cc:
Sent: Thursday January 2 2025 5:11:46AM
Subject: [nanovna-users] Measuring GPS antenna bandwidth

I am building a high accuracy RTK locating system to measure my
property lines and the location of buildings on the property. To
achieve centimeter accuracy, it uses signals from multiple locating
satellite constellations on a range of frequencies between 1164 MHz
and 1610 MHz including those used for American GPS. I have several GPS
antennas, including a couple from high end Trimble survey systems but
am unsure if their frequency response extends far enough beyond GPS
frequencies and how flat the response is.

These antennas have built-in LNA's that utilize 3VDC supplied by
receivers via the coax. The antennas and the LNA's need to be tested
to ensure the system meets the bandwidth requirements. Some of them
can be broken down to access the antenna & LNA separately but I'm
unsure how to inject the necessary LNA DC power without impacting the
nanoVNA measurements.

Does anyone have recommendations for testing antennas with built-in
LNA's?

Regards,
George





Links:
------
[1] /g/nanovna-users/files
[2]
/g/nanovna-users/leave/12583772/4866111/1865567994/xyzzy
 

Dunno how to separate the LNA, unless there's a tiny coax connector behind
it somewhere that you can jack into. I've seen some tiny coax connectors
that were apparently there for testing purposes (or connecting external
antennas) on some of my old cell phones.

Would it be useful to look at noise response graphs on an SDR receiver with
AGC disabled and the gain fixed, while sweeping the frequencies of interest?

You'd still be measuring response of both the LNA and the antenna at the
same time, but it might give some idea if the combination has significant
falloff in the frequency ranges you're interested in.


--
--Bryon, NF6M
 

Would the right approach be to use Port 0 (the source) on the VNA to drive a broadband probe (non trivial) and use Port 1 to measure the response of the antenna/LNA combination. ?You can calibrate your probe by the three cornered hat approach with 3 (notionally) similar antennas. Or choose a probe that is “known by design” (like a NIST standard gain horn or dipole).

If you’re looking for “survey” accuracies (cm or mm) there’s a lot of angle of arrival differences, although a good choke ring/artichoke antenna will have the phase center move by a mm or so over +/- 60 degree from zenith. ?UNAVCO has data on a lot of antennas on their website.

GNSS Antennas - Knowledge Base ( )
kb.unavco.org ( )
favicon.png ( )

( )

If you check the time-nuts mailing list, there’s a fair amount of info on improvised GNSS antennas with very good multipath rejection. Probably about 10 years ago.

Time-Nuts -- Precise Time and Frequency for Amateurs ( )
leapsecond.com ( )
apple-touch-icon.png ( )

( )


On Jan 2, 2025, at 09:33, Ted Chesley <tedchesley@...> wrote:


? Hi George, Look up "Bias Tee Power Injectors" on Amazon.Lots of them
at $15 or so with stated bandwidth to 6GHz.

-----------------------------------------From: "George"
To: [email protected]
Cc:
Sent: Thursday January 2 2025 5:11:46AM
Subject: [nanovna-users] Measuring GPS antenna bandwidth

I am building a high accuracy RTK locating system to measure my
property lines and the location of buildings on the property. To
achieve centimeter accuracy, it uses signals from multiple locating
satellite constellations on a range of frequencies between 1164 MHz
and 1610 MHz including those used for American GPS. I have several GPS
antennas, including a couple from high end Trimble survey systems but
am unsure if their frequency response extends far enough beyond GPS
frequencies and how flat the response is.

These antennas have built-in LNA's that utilize 3VDC supplied by
receivers via the coax. The antennas and the LNA's need to be tested
to ensure the system meets the bandwidth requirements. Some of them
can be broken down to access the antenna & LNA separately but I'm
unsure how to inject the necessary LNA DC power without impacting the
nanoVNA measurements.

Does anyone have recommendations for testing antennas with built-in
LNA's?

Regards,
George





Links:
------
[1] /g/nanovna-users/files
[2]
/g/nanovna-users/leave/12583772/4866111/1865567994/xyzzy







favicon.png
apple-touch-icon.png

 

On 02/01/2025 17:33, Ted Chesley via groups.io wrote:
Does anyone have recommendations for testing antennas with built-in
LNA's?
Use a TinySA Ultra to view the spectrum at the LNA output would be a start.


For an antenna receiving both the 1.2 and 1.5 GHz signals you might try:



"K700 Full Band L1 L2 L5 High Precision BeiDou GPS GLONASS Galileo RTK Survey
GNSS Antenna"

Good price, and works well.

Cheers,
David
--
SatSignal Software - Quality software for you
Web:
Email: davidtaylor@...
BlueSky: @gm8arv.bsky.social, Twitter: @gm8arv

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