Answering this specific question... On 30/05/2019 10:42, Augustine Leudar wrote:
... I had some walkie talkies that had a range of one KM with admitedly terrible audio (surely this could be improved) . Whereas Senheiser in ear monitors have a really short distance range of around 40 metres and use much higher electromagnetic frequencies ((863 mhz) . Why is it something cant be done with the same sort of range as the walkie talkies but for.multichammel audio (according to wikipedia 30 - 400 mhz) ?
Walkie talkies run on a 12.5kHz narrow band, and need ~50kHz of channel space. Broadcast quality FM (as in radio mics) uses a channel space of ~250kHz. Given than channel "skirts" are quite a bit wider multiple local channels cannot sit close to each other, and are commonly spaced ~500kHz apart. They also have to avoid numerical frequencies which would cause intermodulation. Thus remarkably few analogue radio channels can fit into a single (8MHz) TV channel space. The usual answer is ~12 at best. Some claim more but range and mutual interference may suffer. With digital modulation this can improve to ~20 because the effects of interference are reduced.
Range is directly related to bandwidth, transmission power, and RF signal-to-noise limitations of the receiver. Narrow band with limited audio bandwidth and restricted (audio) signal-to-noise is a much easier task with a couple of AA cells than 20kHz audio with 100dB (companded) dynamic range. Digital radio mics have been even harder to make that can modulate something that equates to full broadcast bandwidth and dynamic range into the the same 250kHz bandwidth as analogue, and with roughly the same range/battery power.
I've no idea what the .multichannel audio is - can you elaborate? And I can't imaging that there is any spectrum clear in the 30-400MHz region.
Chris Woolf --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on.
