Locus Loran (CsSync/SatMate) Receiver Frequently Asked Questions

The following frequently asked questions are both Timing & Navigation related. If you have a specific question you would like answered, we’d be happy to help! Just contact schweitzer@locusinc.com and pose your question. We’ll respond to you personally, and also post your question here to share with other users.

Q: Why isn’t my receiver working properly?
A: First, try all the steps in section 5.1 of the Reference Manual (Troubleshooting Common Problems). If that doesn’t improve results, then do the following:

• Take several digital pictures of the antenna installation, its surroundings and the cable path.
• Record at least 12 hours of data from the receiver with the following settings: ‘update 60’, ‘format 2’, ‘format notch 1’, ‘format antenna 2’, ‘process toa on’, ‘status v’. Be sure to begin recording data prior to entering the above commands.
• Email the digital pictures and data file to ferrier@locusinc.com.

We will respond as soon as possible with a diagnosis and further steps you can take to improve receiver performance.

Q: Why should the receiver track many more stations than are used in the navigation solution?
A: The receiver should have all chains with a transmitter located within 1000 to 1500 miles (1600 to 2400 km) included in the search list. Even though these chains and/or stations may not be included in the navigation solution, the receiver uses this information to help identify and cancel out cross-rate interference. If you are using the receiver in North America, you probably will not have to change the search list: the factory default search list includes almost all North American loran chains. For current, detailed information regarding loran chains and/or stations, please see the following United States Coast Guard web page: http://www.navcen.uscg.gov/loran/LoranSelectChain.htm

Q: What is TD averaging? To what value should it be set?
A: TD averaging smoothes out time variations in the received pulses. Longer averaging times generally yield more stable solutions. The downside is that they also translate into a position lag if the receiver is moving, such as when used in marine, aviation, and land vehicle applications. An acceptable balance between stability and lag must be found for the application of interest. We generally recommend the following averaging times: Stationary (timing apps) 60 seconds; Marine 20 seconds; Land mobile 5-10 seconds; Aviation 3-5 seconds.

Q: What are notch filters?
A: Various electronic devices and computer screens may produce interference, which can degrade Loran receiver performance. Locus’ Loran receivers are equipped with notch filters to remove interference in the Loran band. These notch filters will automatically find and remove interference. A quick look at the notch report (see section 3.2.3 in the Reference Manual, or also see the '/' command in the Command Reference Guide) can inform a user about how noisy the antenna location is, and may help to choose the best place to mount the antenna.

Q: What is eLoran?
A: In the United States, enhanced or eLoran is a set of proposed changes and improvements to the Loran-C infrastructure. It includes many things, such as transmitter hardware/software upgrades and system operation procedure changes (e.g. time of transmission control). The schedule for completing all of these changes has not yet been finalized.

It is important to emphasize that Locus’ Loran receivers are "eLoran ready", i.e. software upgrades will enable you to take advantage of enhancements as soon as the eLoran system is operational in your part of the world.

Q: What kind of antenna should I use for my application?
A: The E-field can be used in most stationary monitoring (timing) applications where the antenna is mounted outdoors. It is also suitable for some land mobile and marine applications. The H-field can be used for most applications including stationary (indoors and outdoors), land mobile, marine, and aviation. The H-field is particularly useful in aviation applications because it is not affected by precipitation static like the E-field antenna.

Unlike the E-field antenna, an H-field antenna can be mounted indoors in most buildings and still be effective, especially in timing applications. Each potential site should be examined and some sample data taken to ensure performance is acceptable. Beware sources of interference (computer screens and other electronic devices) and large metal objects, including hidden structural components such as I-beams or metal wall studs. It may require some trial and error to determine an acceptable location for the H-field antenna within the building (see also Notch Filters).

Q: Do I need to ground my E-field or H-field antenna?
A: An E-field antenna needs to be well grounded using the shortest grounding cable possible. The performance of an E-field is, generally speaking, relative to its height. The height is measured from the top of the antenna to the ground. By grounding the antenna well, its effective height and performance are increased. On the other hand, an H-field antenna does not operate in this manner, and therefore does not require a ground

Q: Are there any recommendations for antenna placement?
A: We strongly recommend that antennas be placed as far away as possible from metal objects and trees. For roof placements, note that nearby objects (e.g. HVAC units) can distort the field and also cause re-radiation. It is best to move well away from these objects and also to elevate antennas as much as possible (e.g. we use tripods on Locus’ roof).

Q: How is Signal to Noise (SNR) ratio calculated on the Locus receiver? (Advanced users only)
A: The SNR of a station on a Locus Loran receiver is calculated as the Loran pulse amplitude, divided by the RMS noise ahead of the pulse (in a region very roughly 50us long) that is observed after pulse subtraction, interferer notching, and ensemble averaging, corrected back to the ADC input. The amplitude is the nominal pulse amplitude, so conceptually it's measured at the 30uS point, and it's roughly half the peak amplitude of the pulse.

If you ensemble average N Loran pulses, you multiply the amplitude by N but the noise by only sqrt(N), so you improve SNR by N/sqrt(N), which is sqrt(N). This is sometimes called process gain, and it works about the same way in spread-spectrum chipping systems. So to correct the SNR you divide your number by sqrt(N) to take out the process gain again, which refers it effectively to the input.

Since the SNR is also inversely proportional to the square root of the receiver bandwidth, and there is no accepted way to normalize for this, SNR will vary somewhat according to the Loran receiver brand and model.

Q: Where can I get the most up-to-date technical or reference manuals for my Loran receiver?
A: The most recent copies of the Locus Loran Command and Reference manuals are available for downloading in the Tech Support section of this website.