Unlicensed mobile radio (walkie-talkie l ... / 2012-07-03

2012-07-03 Unlicensed mobile radio (walkie-talkie l ... 8 years ago
Unlicensed mobile radio (walkie-talkie like use) in Europe is possible with PMR446 devices which operate on frequencies between 446.0 MHz and 446.1 MHz. PMR446 was introduced in 1998. The original PMR446 standard gives 8 channels where FM analog audio is used. Using CTCSS or DCS codes extra options to distinguish users of PMR446 are available. But these are more 'calling certain users' options than real privacy, a radio scanner tuned to the PMR446 frequencies can receive all users.

Analog PMR446 radios are quite cheap nowadays: when I browse conrad I can find a simple set of 2 PMR 446 radios for Eur 19.99 Audioline portofoon PMR-15 (Conrad Electronic).

A begin of privacy comes at a price: the lowest price for a (single) PMR446 radio with 'scrambler' and a description which suggests extra software is needed to program that scrambler is Eur 135 Midland PMR portofoon set G14 (Conrad Electronic) or Stabo PMR portofoon Freetalk com (Conrad Electronic) or Eur 205 for the PMR-zendontvanger Kenwood TK-3301E (Conrad Electronic) which is advertised as 'professional' which is visible in the price. Diving into a manual shows that the scrambler has an 'on' or 'off' setting, which makes the given privacy limited to "can't be heard on a standard scanner" but a determined listener can determine the scrambling system and listen in.

A newer development is Digital private mobile radio 446 (DPMR 446) which uses frequencies between 446.1 MHz and 446.2 MHz, not overlapping with analog PMR446. There are 16 channels with FSK (frequency shift keying) in a 6.25 kHz wide channel (half that of analog PMR).

I can find exactly one device supporting digital PMR446 on sale: the ICOM IC-F4029SDR professional digital license free transciever and the price I see is 180 UK pound which is also a 'professional' price.

The 'digital' part of DPMR could allow for real encryption, but for as far as I can find it is not implemented, and searching for details about this I find: Draft amended PMR446 ERC_DEC(98)25 which states:
a)that it is not recommended that applications requiring encrypted speech should be used with PMR 446 radio equipment;
It would seem (to me) that adding strong encryption on digital PMR446 wouldn't be too hard, but the standard doesn't have space for it (at the moment). There are options for group codes (just like ctcss or dcs codes in analog PMR446) but it is possible for a (specialized) scanner to ignore all those. ETSI TS 102 490 technical specification: Peer-to-Peer Digital Private Mobile Radio using FDMA with a channel spacing of 6,25 kHz with e.r.p. of up to 500 mW.

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