FM Radio without an aerial…

I haven’t tried this but I am sure it will work fine … the analogue signal part of the converter might not be the best but would be adequate… and after all in the UK FM signals are sent to transmitters using legacy rather low bit (14 bit compressed to 10 bit samples ) NICAM3 companded encoding with a sample rate of 32 kHz. It is dynamically lossy… Online digital streams have higher definition and wider audio bandwidth (by quite a margin) but rely on psychoacoustic compression (like AAC, most streamed TV, mp3 and Ogg) unlike the UK’s FM sample companding compression.

FM is relatively easy to do in a quality way, unlike AM. The consideration to me will be signal level…for the device to be legal to operate the FM signal output (ERP) will need to be very low.
BTW ERP is defined by antenna gain and power output. Ie by putting a high gain antenna on a low power transmitter you can make it illegal to operate.

Now if you are operating illegally it’s only likely to be an issue if someone complains, ie they are hearing your signal and it’s causing interference… at which point things could get tricky for you. So put antenna where it is well attenuated by your house and use a lossy antenna. Go outside your house into your street and garden and check you can’t hear your signal… you almost certainly will then be fine.


I’m not really sure I’ve understood any of that, Simon, but thanks for replying! You know me, simple guy with a NAT05, and a Yagi on the roof.

My hope was that you or @Mike-B, or both, would be able to help the OP because you both seem incredibly knowledgeable about FM, and have helped me many times in the past. Which is a round-a-bout way of saying thank you to you both.


Hi Simon - thanks for your reply…

Are you aware of any stand-alone modulators (ie not transmitters) that might be connected directly to a tuner input? Now almost certainly academic interest only!

Although it would also be interesting to discover if people’s preference for fm is primarily a result of the transmission chain - NICAM3 distribution and Optimod compression (which I understand is more compressed at ‘drive time’… ) - or something else entirely. It’s not just the ‘sound’ of Naim tuners - there are many fans of analogue tuners in general.

Apparently - if I wanted all my audio to sound like a radio broadcast, I should be able to route it through Stereo Tool software…

And if anyone is wondering - my original search term should probably have been ‘fm exciter’.

Hi Andy

If it works well I’d be surprised unless the transmitter is designed to do exactly that (like a TV modulator) - you may cause extreme overload - levels of output could be many tens of millivolts and the tuner input at hundreds of microvolts. Id be more inclined to experiment by twisting two wires together - one being the output and the other the input - that will be likely a lossy coupling.

Now as far as FM preference - I think the preference is more about the distribution, transmission, antenna and tuner acting as a rather lossy, convoluted but nice sounding digital reconstruction filter, with I suspect the biggest aspects of the SQ being determined by the tuner itself.

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Yes but even then isn’t it digitized on the way?

Hi Lindsay, yes as I posted yesterday, te radio broadcast distribution path is entirely digital up to the terrestrial (airwaves) stage over 14 bit NICAM3.
S-i-S’s post this morning has more detail


The boxes intended for automotive use loop into the aerial feed to the head unit and enable connection of phones et al to units without aux in or Bluetooth - but at ~£20 I couldn’t hazard a guess at how good they are.

Unless someone gifts me a NAT05 I think I’ll stick with the internet feed… :wink:

Isn’t the Nicam3 FM signal digital not analogue?

Yes,but it’s done with no bit-reducing perceptual audio coding.

Isn’t it 14-bit digital which is not a high level (lower than mp3)?

Don’t most people also think, wrongly, that FM is analogue?

fully agree. we must be audio brothers!

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I am so JEALOUS of your DBL btw.

Thank you, yes they are marvelous.Someday I will buy a NAT01 again :sparkles:

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I would recommend to compare a FM tuner to your streamer,I think you will be amazed.
FM is analogue.

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Well all sound is analogue, but I think we’ve established that BBC radio is digitised before transmission. Perhaps you have access to other channels that don’t do this?

Transmission is the key.

IME FM radio - listen to Beeb R3 am and at 5pm daily - it just has a slightly more mellow sound compared to iRadio.
Realistically there is little to choose.
I have long been a radio listener going back…well a long time.
FM radio does at least broadcast to time - sometimes the digital streams can be quite delayed, which I find strange if more than one unit is playing.
Coincidentally, just taken the plunge on a Nat02 to join my Nat01 - fed by G17.


Please explain…

No bit-reducing perceptual audio coding and analogue FM transmission is better than streaming.

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