UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - 87.9 MHz FM Car Radio receives phone calls. Explanation?

SiriusHardware · 16th Aug 2021, 3:47 pm

At one time, with respect to PMR frequencies, there was something called 'M' band where the TX frequencies were in the region of 109 MHz upwards and the RX frequencies were around 139MHz - so there were a lot of utility companies and yes, police transmissions which could be received in the upper part of the broadcast FM band for quite some time before the majority moved to 68-88MHz or 158-170MHz (roughly). Another peculiarity of 'M' band was that both AM and FM modulation appeared to be allowed on that band, some of the synthesised Dymar PMR radios for that band could be programmed to 'be' either AM or FM according to user requirements. So some of the transmissions you might have heard on 'M' band may have been difficult to tune in properly. Even FM transmisisons would have been rather quiet, having only a fraction of the deviation that a broadcast station would have.

16th Aug 2021, 3:47 pm	#9
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,546	Re: 87.9 Fm Car radio explain At one time, with respect to PMR frequencies, there was something called 'M' band where the TX frequencies were in the region of 109 MHz upwards and the RX frequencies were around 139MHz - so there were a lot of utility companies and yes, police transmissions which could be received in the upper part of the broadcast FM band for quite some time before the majority moved to 68-88MHz or 158-170MHz (roughly). Another peculiarity of 'M' band was that both AM and FM modulation appeared to be allowed on that band, some of the synthesised Dymar PMR radios for that band could be programmed to 'be' either AM or FM according to user requirements. So some of the transmissions you might have heard on 'M' band may have been difficult to tune in properly. Even FM transmisisons would have been rather quiet, having only a fraction of the deviation that a broadcast station would have.