[time-nuts] Low SNR GPS reception and cheap LNAs

[Attila Kinali]

On Fri, 25 Apr 2014 08:42:16 -0700
Chris Albertson <albertson.chris at gmail.com> wrote:

> You best bet is to change out the antenna.  You can buy them with a higher
> built-in gain up to about 40dB.   

Buying a better antenna is also on the list. But i would still like to
have an LNA, even if it's just to see that it doesn't help :-)

> My understanding is that designing a GOOD
> LNA is not so easy as little things like the exact layout of the PCB and
> how the PCB transitions to connectors matters a lot. 

Well, the idea is to use one of the monolitic types like the TQP3M9036 [1]
which basicall only need power on the output. These should work quite
well without a PCB. Though i'm really thinking about getting a small
PCB run, both for my bias tee and the LNA, but that will incure a minimum
cost of around 100EUR (same price whether i buy 1 or 10, though)

> But you can buy these
> ready made for cheap.  I've seen complete LNAs in an enclosure with
> connectors at good prices on eBay.    The user manuals I have say using 75R
> cables with compression type F connects is OK.    I doubt the cheaper type
> f-connectors would work well.

I looked at the ones available on ebay, but they were either made for
sat solutions and require 12V, which would complicate the whole power
supply system. Or are >100USD. Given that i can get a cheap LNA chip for
1USD or an expensive one like the TQP3M9036 for 4, then i can build one
myself for less than 20USD that should do the job just as well.


> I have a good high quality Tremble in-line amplifier with N-connector and
> the ability to pass DC.   In my experiment I place the antenna indoor and
> use amplifier and then outdoors with no amplifier.  I get MUCH better
> results with my 26dB gain antenna on the roof and 25 feet of cable than
> with indoor amplified antenna with short cable.      My un-scientific
> conclusion was that amplified noise is still noise.

Well, GPS signal is mostly noise anyways ;-)
The idea would be to place the LNA close to the antenna, in order to
need less amplification in the bladeRF. And also to compensate for
the longer cable i plan to use (getting the antenna to a better location)
 

			Attila Kinali


[1] http://www.triquint.com/products/d/DOC-B-00000120

-- 
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