NATO preoccupata per i rumori del PowerLine

La NATO ha reso pubblico un lungo documento che analizza il potenziale effetto interferenziale di tecnologie come xDSL e Powerline Communication (Internet sul rame dell'elettricità) sulle comunicazioni HF. Ringrazio Andrea Borgnino per avermi girato prontamente il link a questo documento. Ma come? Se andiamo scrivendo da anni che le comunicazioni militari si trasferiscono su satellite e buonasera? Il trasferimento c'è stato ma forse stiamo esagerando, perché la stessa NATO nel 2001 scriveva ("Position on the use of the lower part of the HF band by the military (1.5 – 12 MHz)"):

The HF range between 1.5 -12 MHz is of critical importance to several classic radio communication services and their respective users. Even if in the recent past the military appeared to be shifting away from the HF frequency band as a primary means of communications due to the increasing availability of satellite communications and a demand for larger data transmission rates, the technological improvements in HF transmitters and receivers, especially the use of digital technology and of frequency adaptive systems again have made HF a viable primary means of communications for military purposes.
So, HF continues to be a pillar of tactical communications particularly when working with large coalitions and/or large task forces, where diversity enables better tactical information flow. Other new technologies, such as software programmable radios, tactical PC to PC data transfer and multi-path communication links incorporating HF provide the military large opportunities to continue to optimise the HF band as a viable resource.

Ora, dal lungo e dettagliato studio "HF Interference, Procedures and Tools", si evince che i militari high-tech della NATO guardano con una certa preoccupazione all'aumento della soglia di rumore elettrico nel loro ambiente operativo fatto di comunicazioni tra forze amiche in campo e di SIGINT (intercettazione delle comunicazioni altrui):

a) The cumulative noise field strength due to the PLT emissions may have a possible detrimental effect upon military HF radio communications and COMINT systems. This is particularly the case if In-House PLT systems should become widely popular. However, it should be noted here that the determination of the nature and the severity of any possible detrimental effect upon the military systems was outside the RTG’s expertise and ToR.

b) The HF noise level in the vicinity of PLT installations has been considered in numerous other studies. One study concludes that interference from PLT to a station receiving low-level signals is likely at distances up to 460 m from a single Access PLT installation using overhead power lines. On the other hand, in sensitive receiver sites, the user generally can be assumed to have control over the vicinities, such that a protection radius of up to 1 km, without PLT installations, can be employed. In this case, the cumulative effect of long-distance propagation from a large number of PLT installations may be a more serious problem that requires careful consideration. Therefore, the RTG chose to focus on this less-studied problem.

c) PLT rather than xDSL will cause the most problems regarding HF interference because:

• PLT devices and the power lines that carry PLT signals have the potential to act as unintentional radiators. The amount of radiation depends on the symmetry of the network at radio frequencies. Symmetry is related to the difference in impedances between conductors and ground, where perfect symmetry corresponds to equal impedances. PLT lines have poorer symmetry than xDSL lines, and will also exhibit impedance discontinuities. Any impedance discontinuity in a transmission line, which may arise from a PLT coupling device, a transformer, a branch or a change in the direction of the line, may produce radiation directly or by reflections of signals forming standing waves that are radiated from the conductors. Even if the RF energy is injected into one of two or more conductors, the remaining wires generally act as parasitic radiators and, therefore, the lines can act as an array of antenna elements at certain frequencies. Radiation may come from one or more point radiators corresponding to the coupling devices, as well as one or more power lines.

• A great number of PLT In-House systems (e.g., HomePlug) are expected to be deployed. Such products are readily available on the market and can be installed by anyone, with no verification of the quality of the installation.

• VDSL variants covering the whole HF range are still in the definition phase. Eventual implementation of these systems has not been in sufficient numbers to raise potential interference issues, in the time frame of this RTG. The other versions of xDSL have no documented HF interference-causing problems, therefore the RTG chose to focus on PLT as a noise source.

Insomma, PowerLine genera rumore ambientale reirradiato e può seriamente perturbare le normali attività di ricezione. Per fare la guerra le onde corte servono ancora e i provider dei servizi di accesso a Internet attraverso i cavi elettrici farebbero bene a tenerne conto (i pareri negativi espressi dai poveri radioamatori di solito vengono accantonati come ridicole paranoie). Non so se considerarla una buona o una cattiva notizia.