FM Radio Broadcasting Data System

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lindon105
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FM Radio Broadcasting Data System

Post by lindon105 » Sun Aug 12, 2018 1:32 pm

3 local stations have RBDS. I receive RBDS information from 2, but not the 3rd. Why is that? Does the 3rd have a weaker signal than the other 2? Is there a way to measure RBDS signal strength?

TPT
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Re: FM Radio Broadcasting Data System

Post by TPT » Sun Aug 12, 2018 3:29 pm

Most likely weak signal--or possibly you are in an area with a lot of multipath (reflections off buildings/hills). What are you listening on? If you get a display on your car radio on the other two stations, either the signal is just too weak or they have the RDS subcarrier turned off. You can always see if it is just weak signal by taking a drive towards that station's transmitter...they might just have it turned off for some reason.

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Deep Thought
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Re: FM Radio Broadcasting Data System

Post by Deep Thought » Sun Aug 12, 2018 4:51 pm

Not everyone runs RDBS. It's an audio subcarrier and has no "signal strength".
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lindon105
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Re: FM Radio Broadcasting Data System

Post by lindon105 » Sun Aug 12, 2018 5:18 pm

My in house radios are a Sangean and a Roberts. The car radio receives all 3 while parked in the garage, so it's not a case where a station has RDS turned off.

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Re: FM Radio Broadcasting Data System

Post by Deep Thought » Sun Aug 12, 2018 5:39 pm

Probably just a receiver issue then.
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DaveSt
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Re: FM Radio Broadcasting Data System

Post by DaveSt » Sun Aug 12, 2018 10:49 pm

There are a few things that can affect RBDS reception other than a weak signal or multipath. Most obviously the RBDS subcarrier level needs to be correct. That would typically around 3kHz. Too high is just as bad as too low. There are various mod monitors that can measure that directly. Then anything that degrades the signal to noise around the 57kHz RBDS carrier in the composite signal. That could be a noisy composite STL for example. In the past I have seen a combination of aggressive processing, stereo enhancement and composite clipping cause the RBDS to become unusable. Poor 15kHz filtering on older processors is also an issue.

And finally, having more than one RBDS encoder active is not going to work out well. I once worked on a station that ended up with three active. One in the processor, a second stand alone and a final one built into the transmitter. A consequence of upgrading equipment without having someone that knew what they were doing.

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Re: FM Radio Broadcasting Data System

Post by TPT » Mon Aug 13, 2018 6:38 am

3% of total modulation, not khz. Higher injection level helps--to a point--U.S. allow 5% additional modulation (to 105%) for all subcarriers.

Had an Omnia One install at a classical music station. Put it in, rough set-up using the VU on the exciter--then went for an external antenna when my mod monitor gave me strange results. Very noticeable whistle on the car radio--came to find out the SCA level was wide open on the Omnia, putting noise into the system.

Typically not the problem with most RDS generators, and since the RDS subcarrier is at 57 khz. usually if the stereo signal is degraded the RDS will be affected as well (stereo subcarrier at 38 Khz has energy up to 53 khz.)

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KPJL FM
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Re: FM Radio Broadcasting Data System

Post by KPJL FM » Mon Aug 13, 2018 7:09 am

If it's a HD station, you won't see RBDS when the HD is being decoded. You'll get the PAD data, if they have any.
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Re: FM Radio Broadcasting Data System

Post by NECRAT » Mon Aug 13, 2018 7:59 am

KPJL FM wrote:
Mon Aug 13, 2018 7:09 am
If it's a HD station, you won't see RBDS when the HD is being decoded. You'll get the PAD data, if they have any.
Depending on the model of the receiver. Some won't switch over to the PAD data until the HD is actually locked in.
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