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Band II FM signal and audio level

 
Alex728
(@alex728)
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This seems like a bit of a daft query and probably something I *should* know after all these years, but I'm trying to help improve audio quality at Felixstowe Radio (I volunteer at both this station and ICRFM at Ipswich)

We had to move the soundprocessing to the TX site as the studio got burgled and someone tried to nick it (but left the unit behind) so all the audio levels need to be correctly balanced again (the studio to transmitter link is via an Internet stream). I managed to help the lad who also does the engineering to do this by ear listening in the Felixstowe high school car park - because of Covid19 and my day job employers (a healthcare organisation) instructing me to avoid high risk areas I couldn't visit the TX site along with him (its in the main building of the high school!)

The Band II signal isn't quite strong enough to reach my house in SW Ipswich so I need to drive closer to Felixstowe to get good reception.

As I cross the Orwell Bridge and proceed closer towards Felixstowe, not only does the signal improve (as expected) but there is quite a large jump in the audio level on my car radio - unlike ICRFM where as I drive away from the other high school in Ipswich where the TX is the signal fades out but the audio level remains relatively constant.

Both stations use the same Behringer soundprocessing unit with the same settings.

What would cause this? I suspect the programme audio level to the Felixstowe transmitter (even after soundprocessing) is lower than it should be (so the noise is having more of an effect?)

I don't remember noticing this as much when I was younger and lived in Caversham, Reading but would listen to many London radio stations such as Capital and BBC Radio London/GLR as well as the occasional pirate station from west London (although this was usually in mono on a 1970s era JVC receiver), nor on the various stations I was a DJ on in the 90s..

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Topic starter Posted : 08/10/2020 12:01 am
irob2345
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Do you have access to a spectrum analyser (RF, not audio) that covers Band II?

Are you transmitting in stereo?

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Posted : 08/10/2020 4:58 am
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Doz
 Doz
(@doz)
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I've noticed a similar effect with my current car radio. When the signal level drops, and the stereo decoder gives up, the mono reception is very much quieter than the stereo. It's odd, as the unit has DAB too, and if, for example I have BBC Radio 4 on, and it loses DAB reception, it switches almost seamlessly to VHF FM, and there's no change in audio level until it loses stereo, which frequently happens on a journey to my parents. 

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Posted : 08/10/2020 9:26 am
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Alex728
(@alex728)
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@irob2345 I do, and the transmissions are stereo - it does also sound like what @doz mentions about the stereo decoder cutting in (I guess in my mind I'm still expecting to see a red LED on the car radio for whether the pilot tone has been received ? )

This week the young lad was able to go up to the site with another chap who has worked in broadcast engineering and is semi retired and they corrected some wiring errors, so things are starting to sound better (it will take a few visits to sort this out, made more complicated by having to work blind)

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Topic starter Posted : 08/10/2020 11:44 pm
irob2345
(@irob2345)
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Yes, I was thinking that with the SA you could look at the sidebands to confirm your deviation is the maximum you are allowed.

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Posted : 09/10/2020 12:23 am
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