Wednesday, September 18, 2019

US Government Report on 32-42 MHz from 1998

Thanks to Rob, PE9PE who sent on an interesting link recently about a US government report about the low VHF spectrum from 32 to 42 MHz.

After a bit of research, I established that the report titled "NTIA Special Publication 98-36 SPECTRUM REALLOCATION REPORT" was from February 1998.

The report looked at who the existing users were in this part of the spectrum and whether some of the frequencies could be reallocated to commercial interests.

While the full report looked at several different bands, we'll concentrate on the low VHF spectrum here.

I have included sections of interest from the report below with certain key points highlighted in bold.

It might be worth pointing out that antennas for low band VHF tend to be very large compared to those for the higher VHF and UHF bands. For example, a full size quarter wave ground plane antenna is roughly 2.5 metres on 30 MHz and 2 metres on 40 MHz.

While the report is over 20 years old, it does show that even back then there was little commercial interest in the 30 to 50 MHz spectrum.

INTRODUCTION In the previous section, the bands to be considered for reallocation for non-Federal use were identified. All of the bands being considered for reallocation are used by the Federal Government agencies, in varying degrees, to support Presidential and Congressionally mandated missions. A band-by-band assessment of these factors is presented and recommendations are made as to which bands will be included in the spectrum reallocation plan.32-33, 34-35, 36-37, 38-39, AND 40-42 MHz 

Band Usage 
The Department of Defence (DoD) uses the frequency bands between 32-42 MHz for tactical communication using the Single Channel Ground and Airborne Radio System (SINCGARS) and other land mobile radio (LMR) assets (e.g., Scope Shield II) as well as some non-tactical intra base radio functions.

The Department of Energy (DOE) uses the bands between 32-42 MHz at their Albuquerque,Nevada, and Richland Operations Offices for wireless microphone, LMR, and meteor burst communications. These bands support the DOE statewide Public Safety Net which includes fourteen mountain top repeater sites and the perimeter security device used at the Nevada Test Site. A single frequency is also licensed nationwide for DOE emergency services.

The Department of Interior (DOI) also uses these bands to provide communications inregions that encompass large geographic areas, such as national forests, national parks, wildlife refuges, and Indian reservations. 

The bands between 32-42 MHz are part of what is referred to as the lower Very High Frequency (VHF) spectrum. These bands are used by the Federal Government primarily for providing tactical and non-tactical communication. Because of the unique propagation characteristics in this region of the spectrum, wide area coverage is possible with a minimum number of transmitters. One type of communication that can only be supported in the lower VHF spectrum is meteor burst communications. It has been determined that the 40-42 MHz band is the optimum band for meteor burst systems because there is a somewhat larger meteor scatter signal return and greater channel throughput.

The DOE Meteor BurstSystem does need to operate in this band due to RF propagation characteristics, although it can be replaced by a satellite communications system. The DOE estimates that the cost to replace the Meteor Burst System is $300,000.

Radio waves with frequencies in the lower VHF can be reflected for distances up to 2000 km form the ionized trails that are produced from meteors that enter the Earth’s atmosphere.

The difference in RF coverage between 32-42 MHz bands and the other available VHF/UHF LMR bands is significantly different.

It was determined by the PSWAC that the spectrum from 30 to 50 MHz is good for wide area coverage from mobiles to dispatch centers in open terrain.However, it was determined that portable radios operate poorly due to antenna limitations. Frequencies in this part of the radio spectrum were also found to be subject to “skip” interference between widely separated systems. The bands between 30-50 MHz are in a region of the radio spectrum where the ambient noise levels are high, particularly on highways and near industrial areas.The increased noise levels can limit the performance of a communications system by restricting the operating range, generating errors in messages and data, and in extreme cases preventing the successful operation of a receiver. Moreover, the availability of equipment in the lower VHF band is questionable. Both Ericsson and Motorola have indicated that they will no longer manufacture equipment capable of operating in the 30-50 MHz frequency range.13 The PSWAC concluded that these technical constraints impair future use of the band to satisfy public safety spectrum requirements.14 3-3

Public Benefit Operating frequencies for new commercial services must be chosen in a region of the radio frequency spectrum where: it is possible to use efficient compact antennas; equipment can readily be made available; and where interference can be minimized. In the 32-42 MHz bands the technical constraints and questionable availability of equipment will be limiting factors in the development of a new commercial service. In identifying bands for possible reallocation, Title III of the BBA 97 specifically requires the Secretary of Commerce to consider the extent to which equipment will be available that is capable of utilizing the band. This would include any technical constraints that would contribute to the unavailability of equipment. Reallocation of spectrum in these bands may not be consistent with Title III.Reallocation Options Reallocation of the Federal Government bands in the 32-42 MHz frequency range for private sector use would result in little or no benefit to the public. For this reason, reallocation of these bands was not considered to be a viable option.

1) Report introduction

No comments: