Signal and noise - Peter Monta

Xona X5 data

Peter Monta — Sun, 17 Aug 2025 12:45:00 -0400

The 10230-chip Xona X5 data code has been added to my Github repository:

https://github.com/pmonta/GNSS-DSP-tools

The signal is somewhat different from a "normal" GNSS data signal in that each code period has the code shifted by an amount equal to the data symbol sent during that period …

Xona X1 pilot and data tracking

Peter Monta — Mon, 11 Aug 2025 18:30:00 -0400

I've added the Xona X1 pilot and data codes to my Github repository supporting the various GNSS signals:

https://github.com/pmonta/GNSS-DSP-tools

There are also preliminary acquisition and tracking programs similar to the others. In the case of the Xona signals, though, they really need either external aiding or …

Xona spreading codes

Peter Monta — Fri, 08 Aug 2025 12:30:00 -0400

The spreading code for what appears to be the pilot component of Xona's X1 signal is shown here:

After carrier wipeoff, the signal is sampled at 1.023 MHz and coherently integrated for 800 ms. The code chips are clearly apparent, and they have a 4-level structure because of the …

GNSS signal from Xona's Pulsar-0 satellite

Peter Monta — Wed, 30 Jul 2025 22:50:00 -0400

This waterfall plot shows the L1 signal from Pulsar-0:

The frequency is as expected, 1593.322500 MHz give or take the Doppler shift (that is, a nominal carrier frequency of 155.75 times 10.23 MHz), but, curiously, the bandwidth appears to be only ~1.7 MHz rather than the …

Compact Disc microscopy, part 2

Peter Monta — Sat, 14 Jan 2023 02:30:00 -0500

See part 1 here.

In order to capture and decode more bits from the CD's surface, multiple images are needed. Below are 125 images forming a short arc (roughly following the CD's tracks) stitched with Hugin. (Other stitching tools include MIST and Ashlar, though MIST assumes a regular grid structure …

Compact Disc microscopy

Peter Monta — Thu, 22 Dec 2022 11:48:00 -0500

While refining my CNC microscope setup, I thought I'd have a look at some CD surfaces. Unfortunately CDs are not especially useful as calibration artifacts, since the track pitch and channel-bit length can be varied over ~15% ranges and still be in spec (manufacturers played with these parameters to pack …

Clean version of Logarithmorum Chilias Prima

Peter Monta — Thu, 18 Aug 2022 12:18:00 -0400

Logarithmorum Chilias Prima is the first table of base-10 logarithms, written by Henry Briggs and published in 1617. I've previously taken a look at the accuracy of the table entries.

I thought it would be neat to have a faithful copy of the original printed version. To this end, the …

GNSS sky recordings

Peter Monta — Sat, 01 Feb 2020 10:06:00 -0500

I'd like to make available to a wider audience a stream of GNSS sky recordings.

The recordings are made with the GNSS Firehose digitizers and Tallysman TW3972 antennas. Each recording is 200 ms long and contains three GNSS bands, each sampled at 70 MHz with a useful bandwidth of about …

The L1C signal on GPS III

Peter Monta — Wed, 27 Feb 2019 01:19:00 -0500

The recently-launched GPS III satellite, SVN 74, is transmitting on PRN 4, though not yet set healthy. But it's a good opportunity to have a look at the L1C signal.

The pilot is TMBOC; here is its correlation peak:

It looks proper to me, though I haven't compared it against …

BeiDou B2b codes

Peter Monta — Mon, 24 Dec 2018 10:10:00 -0500

It turns out to be an interesting exercise to extract the BeiDou B2b codes from GNSS recordings. If there were a pilot on B2b, there would have been plenty of SNR with even a short recording to see the pilot using a technique similar to that shown by Yudanov [1 …

GNSS tri-band, quad-constellation sky recording

Peter Monta — Mon, 15 May 2017 10:54:00 -0400

I'd like to share my first tri-band GNSS sky recording along with scripts for acquisition and tracking.

The recording is 50 seconds long with three channels of simultaneous 2-bit complex samples at 70 Msa/s (approx. 50 MHz usable bandwidth per channel) centered on L1, L2, and E5 (~1191 MHz …

GNSS Firehose update

Peter Monta — Fri, 05 May 2017 00:06:00 -0400

Some updates on the GNSS Firehose system as it approaches general usability:

now supports three 50 MHz RF channels (nominally covering L1/L2/E5), 840 Mbit/s total payload
supports command and status over Ethernet (in addition to UART)
firmware now in C, running on a RISC-V soft CPU (picorv32 …

GNSS Firehose status, example L1/L2 sky recording

Peter Monta — Sun, 10 May 2015 21:30:00 -0400

Just a quick update on the GNSS Firehose digitizer project. I've decided to get a few systems professionally assembled; they will be similar to this prototype unit:

Here is some sample data, a sky recording taken on May 6 at around 13:38 UTC:

gnss-3.dat (743 MByte)

This represents …

Squaring receiver for Galileo blind search

Peter Monta — Tue, 23 Sep 2014 02:51:00 -0400

I've been following the drama of the two recently-launched Galileo FOC satellites. To my knowledge, nothing is yet known about the status of the transmitters, nor have the PRNs been revealed, nor does an acquisition search over all 50 codes in the Galileo ICD yield any signals when the satellites …

GNSS stamp collecting

Peter Monta — Tue, 16 Sep 2014 01:38:00 -0400

Here's a fun montage of the various GNSS signals-in-space. I think this accounts for all extant open-access signals that are likely to remain so (ruling out Galileo E6 for example) and that are intended for systems having global coverage (so no QZSS or IRNSS). A few comments on the signals …

Height-based multipath mitigation

Peter Monta — Sat, 06 Sep 2014 23:22:00 -0400

Here's a crazy idea which I might as well put on the blog.

Multipath is an important error source for GNSS reference stations. Monuments for antennas are nearly always placed close to the Earth's surface, so the ground will act as a reflector with a grazing geometry that generates short-delay …

Semicodeless P(Y)-code processing using high-rate aiding

Peter Monta — Fri, 25 Jul 2014 23:55:00 -0400

Present schemes for semicodeless P(Y) processing assume an autonomous receiver that estimates W-code bits directly from the received signal. Given the limited C/N0 available, naturally the signals are noisy, resulting in squaring loss.

One simple way around this is to use more reliable estimates of the W bits …

Parallel processing of recorded GNSS signals

Peter Monta — Fri, 25 Jul 2014 23:51:00 -0400

Most GNSS receivers process signals serially. This is natural for tracking loops based on PLLs and DLLs, as they have a feedback structure. If signals are recorded and stored, however, another viewpoint might be more flexible.

Let's regard the recorded waveform as a series of chunks of length, say, 5 …

GPS P code exploration

Peter Monta — Tue, 08 Jul 2014 06:49:00 -0400

As a first step towards obtaining GPS P-code observables, it seems prudent to verify that the P code is detectable in a test recording with high C/N0.

Here's the result with an L1 recording containing a strong signal from PRN 30 (about 50 dBHz). The peak is smeared over …

New "GNSS Firehose" board

Peter Monta — Tue, 17 Jun 2014 22:39:00 -0400

I've finally gotten around to updating the GNSS front-end digitizer. Along with a new Ethernet PHY chip (the old one from Vitesse seems to be no longer available), there is an external clock option, an expanded auxiliary header, and a number of small improvements in signal integrity. The external-clock header …

SMT stencil cutting

Peter Monta — Tue, 25 Dec 2012 10:56:00 -0500

I've been making some SMT stencils using a Silhouette Cameo craft cutter (vinyl cutter). It's great for fast turnaround time and low materials cost, though the quality is not as high as a laser-cut stainless-steel stencil. Still, they're useful down to 0.5 mm pitch and 0201, and possibly a …

Logarithmorum Chilias Prima

Peter Monta — Tue, 05 Jun 2012 09:54:00 -0400

Here is some analysis of Briggs' first logarithm table of 1617, Logarithmorum Chilias Prima.

The table is available on microfilm as part of the Early English Books series from UMI/ProQuest. The on-line service, Early English Books Online (EEBO), also makes the work available, but the scans are of poor …

GNSS Firehose

Peter Monta — Mon, 04 Jun 2012 20:52:00 -0400

Wideband front end for GPS, Glonass, Galileo, Compass

I've long wanted a fully flexible GPS receiver. Starting from the raw RF samples gives complete visibility into the signal processing and estimation algorithms for the observables. Unfortunately, existing commercial products, either in the test-equipment class (e.g. vector signal analyzer, USRP …

555 contest entries

Peter Monta — Mon, 28 Feb 2011 12:00:00 -0500

Here are my two entries for the 555 design contest.

An op-amp made from 555 chips

Digital logic using 555 chips

Peter Monta — Sun, 27 Feb 2011 12:00:00 -0500

Question: is the 555 complete in the Boolean sense? That is, can any Boolean function be realized as a network of 555 chips?

Answer: yes. Tie the threshold pin high---this essentially disables the 555's internal latch. Now provide inputs to the reset and trigger pins and take the output from …

An op-amp made from 555 chips

Peter Monta — Sun, 27 Feb 2011 12:00:00 -0500

Is it possible to make an op-amp out of nothing but 555 chips and passive components? Not a terribly practical question, given the existence of very inexpensive and capable op-amps covering every corner of op-amp performance space; but it has some aesthetic appeal. If you find yourself on a desert …

Photographic lunar distances

Peter Monta — Tue, 01 Dec 2009 12:00:00 -0500

Update, September 2020: I've written some code to estimate the Moon's position against the stellar background on images similar to those below. It's available at my GitHub repository here: https://github.com/pmonta/lunar-astrometry

These images were taken on November 30, 2009 at 08:29:43 UTC. The location is …

Printable Otis King slide rule

Peter Monta — Mon, 15 Jan 2001 12:00:00 -0500

After looking through Dick Lyon's web site devoted to the Otis King cylindrical slide rule, I decided I had to have one, even if only made of paper. So here's a Postscript / PDF version of an Otis King model L—just cut out the pieces, tape them into paper cylinders …