What bandwidth is needed for RDS - revisited?

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daveB
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What bandwidth is needed for RDS - revisited?

Post by daveB »

I know it has been discussed before - and in my opinion 150 kHz should have been more than enough for weaker signals.

BUT - by accident SDR# had defaulted to 250kHz and when I reset it to 150 kHz it failed to give me RDS on a weak clear signal from KissKiss (Italy).

After multiple checks at different bandwidths I've had to revise my opinion. A weak signal needs maximum bandwidth. In this particular case 180kHz decoded the RDS, 160 KHz was marginal and 150 kHz was no good. (Strong local sigals will give RDS with 100 kHz b/w).

Of course in a crowded band and strong openings 180 kHz or more will drag in adjacent channel problems. So I'm going to stick to 150 kHz (or 140 kHz), but if conditions permit try and squeeze the last bit out of it by widening the bandwidth.

And not forgetting to offeset 10-20kHz away from a strong interfering station - which can produce RDS almost miraculously.

The same thing doesn't really apply to analogue filters which have a much gentler roll off, whereas digital filters drop off like a cliff.
Location: Sittingbourne, Kent JO01ji
SDRPlay, AirSpyMini, RTL dongles, ST311, Yamaha TX930. 5 ele yagi 20ft agl - 70 deg. FM5 - 80 deg, 5.1 Yagi 16ft agl - 120 degFM5 -180 deg. Vert 3-ele Moxon - 80 deg. Shielded magnetic loop 0.1-200 MHz - 10 ft agl

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jotagarzon
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Re: What bandwidth is needed for RDS - revisited?

Post by jotagarzon »

Hi Dave,
Must be something else. I mean that with a well tuned signal and same bandwidth, there are stations showing full RDS data in miliseconds and others still 'thinking' after 30 seconds. Sometimes I have succeed with 100-110 kHz bandwidth and others got just ramdom symbols with 175 kHz. Perhaps the way they adjust subcarrier levels does it affect the RDS reading? (not just this, of course).

But offest 10-20 kHz is always a good trick, that's true!

Saludos

Jorge
Jorge Garzón. EB7EFA / EA1036 SWL
IN83ag Cantabria (Spain) / 43°15'N • 3°56'W
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Rx: RSP1A/AirSpy HF+/Lowe HF 150/Sony SA3-ES-EE
Ant.: Fanfare FM-2G/Wellbrook 1530LN/5el SKT Yagi
Blog: http://iberiadx.wordpress.com

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Patrick73
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Re: What bandwidth is needed for RDS - revisited?

Post by Patrick73 »

Il also depends on the level of modulation.
A low / very low very level will allow decoding at 110-120 kHz BW (especially with a talk program).

The settings on the RDS encoder itself are also to be taken into account.
Patrick
Main interests : NDB, MW & FM DX'ing
REU Editor http://www.classaxe.com/dx/ndb/reu

satnipper
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Re: What bandwidth is needed for RDS - revisited?

Post by satnipper »

The RDS subcarrier is at 57 kHz. If you have a larger bandwidth then you also have more noise I would have thought.

Nick Gilly
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Re: What bandwidth is needed for RDS - revisited?

Post by Nick Gilly »

I get satisfactory RDS decoding using the 114 kHz bandwidth on the RBRX Encore, so I tend to use that as the default when tuning around for DX. It can even resolve RDS from BBC Radio 3 and 4 from Rowridge at 56 kHz.
Good DX.

Nick, Whitchurch, Hampshire.

BW Broadcast RBRX Encore, Kenwood L-1000T, Yamaha T-2, Denon TU-800L, Kenwood KT-1100SD (modified), Yamaha T-85, Sony XDR-F1HD tuners, horizontal Körner 9.2 beam (Antennenland version), Yaesu G-450C rotator

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Julian Hardstone
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Re: What bandwidth is needed for RDS - revisited?

Post by Julian Hardstone »

Multipath signals are a greater problem for RDS than signal level or qrm, so you may get an improvement by offsetting the beam bearing

daveB
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Re: What bandwidth is needed for RDS - revisited?

Post by daveB »

Il also depends on the level of modulation.
A low / very low very level will allow decoding at 110-120 kHz BW (especially with a talk program).
Which should means when the audio goes quiet in a pause you should more likely get RDS decoding?

It also depends on what % of power is assigned to the RDS sub-carrier. From what I've read the level should be about 10% of the total power. Now I have a pirate station on 91.7 PI: 6856 PS: FRONT FM who have the power to the RDSsub-carrier so high I get RDS decoding when the signal is almost at noise level - I am not joking.

My rule of thumb id that if the S/N ratio is 16dB or more you should be able to see RDS - this station is down at 7-8 dB (on SDR#) and still giving full RDS at 50-60% ber on RDSSpy - and on SDR#! This is at 150 kHz b/w. It will produce a pi code at 110KHz. Above 180 kHz and below 130 kHz ber goes up.

I've noted stations from some countries come through at a couple of dB worse SNR nd others need a stronger signal. I'm only referring to signals clear of interference.
Location: Sittingbourne, Kent JO01ji
SDRPlay, AirSpyMini, RTL dongles, ST311, Yamaha TX930. 5 ele yagi 20ft agl - 70 deg. FM5 - 80 deg, 5.1 Yagi 16ft agl - 120 degFM5 -180 deg. Vert 3-ele Moxon - 80 deg. Shielded magnetic loop 0.1-200 MHz - 10 ft agl

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