On Fri, Apr 25, 2014 at 6:28 AM, Attila Kinali attila@kinali.ch wrote:

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

--

Chris Albertson
Redondo Beach, California

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

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 :-)

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)

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.

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

--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin

On Fri, Apr 25, 2014 at 9:04 AM, Attila Kinali attila@kinali.ch wrote:

I'n not a microwave expert at all.  But I took my Trimble amplifier apart
and looked.  They used a chip like you describe and some inductors to
bypass the DC.  The part that is impressive is that they maintained a 50
ohm transmission line all the way fem both N-connectors to the chip.  The
chip fits perfectly on the 50 ohm strip line trace.  The radius on the PCB
traces is just a about right too.

I suppose you could build the same circuit "dead bug" style by soldering
small rg178 coax directly to the IC pins.  I've tried.  I need a low power
microscope to get it right.  But those are available for about $100 on
eBay.  The circuit is more complex if you need to inject DC bias.
Truthfully I'd just buy one.  They make them for cable TV that work for GPS

But I've build tons of stuff, mainly for the education you get.  No hobby
is "practical".

--

Chris Albertson
Redondo Beach, California

On 04/25/2014 06:04 PM, Attila Kinali wrote:

The indoor antenna would see the noise of the house 290-300 K rather
than the background noise of the sky 3 K. The signal will also be
attenuated when indoor.

If you have a passive antenna, put a LNA right at the antenna, since any
cable damping will cause the S/N to go down. Also, if you put an
aditional amplifier in line, your want that too up at the antenna.
Then, low-loss cable should be natural.

Cheers,
Magnus

On Sat, 26 Apr 2014 12:25:11 +0200
Magnus Danielson magnus@rubidium.dyndns.org wrote:

My current antenna is an cheap patch antenna. It has an LNA, but aparently
it's not enough. I talked with a few gnuradio people and they basically
told me that the GNSS-SDR software needs a strong signal for acquisition.
Ie. i realy need to put the antenna somewhere with good skyview.

I ordered 4 of those lna4all, so that problem should be solved.

I'm also getting a better antenna and we'll see how much signal i can
get out of this place.

		Attila Kinali

--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl

Hi

The ability of these receivers to handle noisy signals depends on a lot of things. The good stuff seems to have a massive number of correlators. Going from a 1.3 to a 0.3 db nf amp likely only helps you by 1 db. The low correlateor GPS’s are / were 10 to 20 db less sensitive than the newer stuff.

Bob

On Apr 26, 2014, at 6:52 AM, Attila Kinali attila@kinali.ch wrote:

On Sat, 26 Apr 2014 08:20:47 -0400
Bob Camp lists@rtty.us wrote:

Yes, the sub-optimal correlation system in GNSS-SDR seems to be one of
the problems. But still, the LNA will help with two things: It will
enable me to put the antenna in a better spot while compensating for
the cable loss (i need about 20m of additional cable, which is about 6dB
of loss) and a stronger signal at the bladeRF such that less gain is
needed in the radio chip there.

My current goal is to get a feeling how GNSS-SDR works. After i get
an understanding for the code, i will try to improve on the correlators
in order to improve reception.

		Attila Kinali

--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl

Attila,

On 04/26/2014 12:52 PM, Attila Kinali wrote:

I'm just about to put my double-frequency choke-ring antenna on the top
of the antenna-pole, with support-lines, and then LMR-400 cables to go
into the lab/shaft/mancave.

I hope that will beat the old setup.

I intend to rebuild one of my single-frequency antennas with a new
element and suitable LNAs, and the lna4all looks very interesting.

Cheers,
Magnus

On 04/26/2014 02:59 PM, Attila Kinali wrote:

You probably want to move from the Tong-search (traditional channel
search) to FFT based cross-correlation search. Once the FFT has
determined coarse phase and doppler frequency, you can setup the normal
correlation channel with that and lock into the signal. You can also do
a secondary FFT in order to get higher dopper frequency resolution once
you have the phase. With both phase and doppler found, channel lockin
becomes much quicker as you leave it very near the actual balance-points
and that way you can allow the PLL bandwidth to be much smaller and thus
suppress noise better.

I've toyed with FFT phase correlation and hand-over to the channel, and
for my case it worked really well without too much of code.

Cheers,
Magnus