Radio frequencies for airborne use in the UK

[Ross G6GVI]

Just a reminder that the regulations for airborne radio transmissions in the UK are more restrictive than other administrations, so some of the default parameters used elsewhere in the world must not be used here. But there is still scope within the law for HAB transmissions - see below.

Our regulations state: "It is required by the Wireless Telegraphy Act 2006 that no radio equipment is installed or used in the UK except under the authority of a licence granted by or otherwise exempted by regulations made by Ofcom." Happily, we find some convenient exemptions for airborne use detailed in the document UK Interface Requirement (IR) 2030 "Licence exempt Short Range Devices (SRDs)":

https://www.ofcom.org.uk/siteassets/resources/documents/spectrum/interface-requirements/ir-2030.pdf?v=415472

This is a 128-page tome, but within the table on page 17 there are three UHF allocations in which Equipment may be used airborne: 

There are still three constraints which must be met: frequency, power and "duty cycle" - the latter being the percentage of time in transmit (so 10% is equivalent to 6 seconds each minute). E.R.P. is "effective radiated power", which takes into account any gain of the antenna, but with a little ground-plane or dipole this is around unity.

When setting the frequency, take into account the bandwidth of the modulated signal - so with BW = 125kHz, keep the "dial" (centre) frequency more than 63kHz within the edges of the permitted band (and allow some extra margin for the drift of the transmit oscillator with temperature).

Most of the transmit modules specify a power setting in dBm (deciBels above 1mW), so 1mW = 0dBm and 10mW = +10dBm (+13dBm would be 20mW).

See how these parameters are inter-related: if you want continuous transmissions (100% duty cycle), then either keep the power down to 1mW or the frequency above 434.04 and bandwidth below 25kHz for 10mW (this is why UKHAS LoRa "Mode1" is often used, as it has BW = 20kHz, compared with 62kHz for "Mode2").

Now holders of  a UK Amateur Licence have been permitted airborne operation since February 2024, but limited to 500mW (+27dBm) and only within certain bands, including 14, 18, 21, 24, 28, 50 & 144MHz, but not 432MHz. Transmissions must be identified with an Amateur callsign and the exact frequency and bandwidth is constrained by the particular Band Plan (e.g. WSPR on 14.097, Morse & FSK on 144.020, or FM-APRS on 144.800). There are also clauses in the Licence relating to "Unattended operation" and "Radio beacons".

[M5AKA]

Ross G6GVIU wrote: "the exact frequency and bandwidth is constrained by the particular Band Plan (e.g. WSPR on 14.097, Morse & FSK on 144.020, or FM-APRS on 144.800)"

Why do you say Morse & FSK on 144.020, I can't see that frequency mentioned in the band plan?   

WSPR isn't mentioned in the Band Plan either although 14.097 is the frequency traditionally used.

Trevor

--
You received this message because you are subscribed to the Google Groups "UKHAS" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ukhas+un...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/ukhas/32363c96-23be-48f7-a94d-74e6a61c4447n%40googlegroups.com.

[Ross G6GVI]

The 2m Band Plan shows the segment 144.000-144.025 MHz  for "All modes" with a maximum bandwidth of 2700Hz, so this is where I've been testing a beacon with Horus V3 & CW ident.

The G0BWC 2m beacon flight last September used CW only on 144.091MHz, which is in the "Telegraphy" (500Hz BW) segment.

I don't use HF much, but I see that modes like WSPR & JT8 go in the "Narrow band modes" (500Hz BW) segment.

The important point is to fit in with existing (terrestrial) users of the bands and to keep within the allowed bandwidths - so there's nowhere to run a LoRa APRS signal (125kHz BW) on 2m, for example.

Incidentally, there's a 2m APRS flight (WX8TOM-12) coming in over Ireland at the moment and being picked up by digis & IGates on 144.8.

73 de Ross.