Meth2_WhyaSDR_Why a SDR approach to radio reception for cruisers

Meth2_WhyaSDR

Why a SDR approach to radio reception for cruisers?

Or, given the goals and the available radio sources (check my previous post about the background and motivation ) what are the feasible options  for a cruiser?

Goals: to have a portable, yet easy to deploy, reliable and easy to use system

What radio sources of timely safety warnings, notices to marines and other useful information?

(From my experience mainly by the Iberian Atlantic Coast and the Mediterranean)

And listing such sources, from the lower to the upper radio spectrum, in a language simple to understand for cruisers even if not the most accurate for experts:

Navtex

Similar to verbal warnings and notices through VHF channels but in text format, thus the messages could be checked in a display and/or printed. General architecture of the system is fine. Unfortunately the radio frequencies used (around 500 KHz) are very prone to be impaired by obstacles and all sort of radio and electromagnetic interferences. Up now, I knew only two skippers happy with their Navtex; for myself as for the majority of  skippers I talked to this source, at least through the available commercial systems, is unreliable  and completely useless. It seems navtex is also available, in a few areas, around 2800 KHz, but I had no experience with it.

RTTY-DWD

Warnings and useful information in text format. Not part of the safety, mandatory, SOLAS network but nevertheless regarded by both professional and leisure sailors as a good source. Broadcasted by the German DWD through several medium/high frequencies. A maritime or Ham SSB transceiver coupled with a data/digital system could be used to receive RTTY, but it is an overkilling approach. In fact, it is very easy to receive readable messages even with a dated small receiver connected to an iDevice or a computer running digital modes software.  For example, a Sony ICF-SW7600G. You would receive messages and warnings about all the covered regions, regardless of your actual area of navigation. Quiet funny, to read ice warnings while enjoying a Sun bath in the Baleares.

WeatherFax

Meteo Charts. Very useful. Broadcasted by several USA, UK and German radio stations. Much of the previous comments on RTTY do  apply here.

VHF

Coastal safety, meteo and other useful information broadcasted by national maritime authorities. Voice messages through Very High Frequencies, VHF in short, hundreds of MHz. Usually the first call is issued in channel 16 both in the local language and in English. Easy to receive with almost any fixed or portable transceiver/receiver. Main problems: we just do not listen the messages, radio noise, hard to understand the local language, the proficiency of the radio operator trying to speak in English is not  the best … so recording the messages would be a must.

SafetyNet/EGC

Several types of safety and other useful messages available through the satellites of the Inmersat network. Mandatory for certain vessels. UHF, GHz frequencies. There are dedicated receivers used in large vessels and very expensive offshore leisure or racing boats. For the rest of us a portable satellite phone coupled with a data reader/display is  the most common approach. Nevertheless, even the cheaper satellite phones and communication fares are considered still quite expensive by most cruisers and its use is almost restricted to offshore navigation.

Wifi/3-4-5 G

Yes, lots of useful maritime and meteo sources, web pages and apps. Readily available for coastal navigation, at least in the developed countries. Easy to receive by ordinary mobile phones, idevices and computers. Not part of the mandatory maritime safety networks. Always staying close enough to the coast to receive such “terrestrial”  GHz radio frequencies might not be wise nor safe.  Not the scope of this blog anyway.

So,  repeating the initial question of this post,  why a SDR approach to portable radio reception for cruisers?

First, let us face it, even the “fixed” systems often found in leisure vessels are not satisfactory. Navtex commercial receivers are useless. SSB maritime transceivers and related modems to transmit/receive text and images are expensive, difficult to install and power hungry; and surely overkilling if used  to “just” receiving information. It seems even that nowadays it is impossible to get a new SSB transceiver compliant with the European legislation. Satellite fixed systems are regarded as too expensive for must of us.

Second, there is no such thing as a conventional piece of hardware, a portable classic radio receiver able to cover the entire spectrum for the sources listed above.  My Sony ICF-SW7600G, and similar radios used by sailors, are honorable pieces of technology. Only for SW/MW/LW or FM. As many old school sailors I almost always travel with mine. But for a similar price tag of these old radios we can now buy a far better SDR.

Therefore a SDR, mid range unit with a price tag of 100-300 Euros, seems the best option. Several models in this range are able to cover all the spectrum from the low/medium to the ultra high frequencies. Furthermore, for each radio broadcast frequency we could select the best, built in filter/amplifier. No need to play with several small pieces of hardware, connectors and cables as with those so called “cheap dongles”. Finally, paired with the proper antennas such SDRs could receive all the voice and data messages of interest for cruisers. With a quality that matches higher-end transceivers (check Ham forums, the Akos blog radioforeveryone.com and other commendable reviews).

For example, SDRplay RSP 1A (for single antenna coupling) or the 2 or Dx models, that might be paired with up to three antennas simultaneously, thus really covering all the spectrum of interest for us. Ie., (1) a simple wire antenna for navtex, rtty, weatherfax and M/L frequencies in general, (2) a VHF one for well … receiving/recording vhf channels and (3) a patched or equivalent antenna for receiving data from satellites.

 (more on technical specs, examples and tests of SDRs, antennas  and software in future posts).