RSP2 & NDB RECEPTION

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Paul
Posts: 90
Joined: Fri Feb 17, 2017 9:52 am

RSP2 & NDB RECEPTION

Postby Paul » Sun Aug 06, 2017 7:33 pm

Has anyone on this forum successfully received NDB morse signals using the RSP2?
if yes, I would be interested in what settings were used to achieve this.
The SDR at Twenthe university in the Netherlands receives the Bottrop NDB (BOT), appears to be on CW 403KHZ but the morse signal is only received on 403.75KHZ USB.
My setup works completely satisfactorily within it's capabilities and I am quite able to receive morse code CW signals all over the bands - but not in this part of the MF band, in which I find no lack of signals of various types, such as NAVTEX, which of course is a very powerful signal (and so received).
Tuning in to known NDB carriers in CW appears to be accomplished correctly, but no morse signals are apparent and switching to USB hasn't yet accomplished anything either.
It may, of course, be some sort of deficiency in my setup, but just what eludes me as it appears to "tick all the boxes."

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g1hbe
Posts: 228
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: RSP2 & NDB RECEPTION

Postby g1hbe » Sun Aug 06, 2017 11:26 pm

Hi Paul. I often listen to NDB's in that part of the band and I can hear quite a few of them. I find I can hear them a lot more clearly if I switch in a 500 KHz LPF. Mine is homebrew but you can buy them. I think the problem is the massive signals coming in from the MW AM band, so the LPF cuts them out and allows the RSP to work better.
Bear in mind that the beacons are transmitted as conventional double sideband AM, with the morse ID carried as 500 Hz tones. Listening in 6k AM should work, but also any of the SSB modes should work too. Listening on the narrow CW modes may mean you have to tune 'off frequency' to hear the tone.
The last thing to mention is that the SMA inputs are poor at low frequencies (high noise level) so the hi-z input is recommended.

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Andy

Paul
Posts: 90
Joined: Fri Feb 17, 2017 9:52 am

Re: RSP2 & NDB RECEPTION

Postby Paul » Mon Aug 07, 2017 6:32 am

Thanks for the response Andy - I'm a little (much) wiser after that.
I have tried both Ports A (active mini-whip) - that does seem to perform well in the range) and also a longwire to the Hi-Z Port.
Both appear to receive CW carriers well, but not a peep of the tones.
I will of course give our suggestions a good go - but perhaps without an lpf I'm "on a hiding to nothing," as you say, the band is crammed full - I have tried the built in MW/FM notch, which is effective, but my impression is that it seems to degrade "wanted" signals as well, so if they are at all tenuous, you're also on a loser.

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Paul
Posts: 90
Joined: Fri Feb 17, 2017 9:52 am

Re: RSP2 & NDB RECEPTION

Postby Paul » Mon Aug 07, 2017 7:24 am

A second thank you Andy
1. Success - finally! - AQC (AQABA) on 346.468 (USB)
2. I now know the "shape" of a NDB signal, which of course is most helpful
3. The mini-whip worked better, so I'll see if the Hi-Z input can be improved.
It's taken me quite a long time to get to here...and wouldn't have without you help.

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g1hbe
Posts: 228
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: RSP2 & NDB RECEPTION

Postby g1hbe » Mon Aug 07, 2017 6:45 pm

That's great, Paul. It's quite fascinating to listen down there and even more interesting when you start really plumbing the depths below 100KHz. BTW, I use a Wellbrook 1530 loop antenna as the noise level around here is monumental and trying to hear anything at low frequencies on a conventional wire aerial is useless. The Wellbrook cuts the noise like you wouldn't believe, and as it is a wideband design there is no tuning to do, meaning it can be mounted outside (perhaps on a cheap rotator) as you don't have to reach it.
The 60 Khz signal from MSF is virtually inaudible on my various wires, but as soon as I select the loop up it pops at good strength. There are lots of other time-signals to hear and some tele-control stuff too.
My 'acid test' for homebrew loop antennas is whether they can hear the stuff down around 22 KHz. The Wellbrook is just about losing it at this frequency (not surprising as it is specified only down to 50 KHz I think). Even trying to equal this performance with homebrew loops takes some doing. It's all good fun, but noise is the enemy!
Good luck with it, I'd definitely recommend a set of filters for your RSP. Like all wideband SDR's, it has to use wide front-end filtering or the waterfall display won't show much.

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Andy

JMG
Posts: 17
Joined: Thu Mar 26, 2015 9:58 pm

Re: RSP2 & NDB RECEPTION

Postby JMG » Wed Aug 09, 2017 8:25 am

You may take a look at the navy-signals at 20kHz. The narrowband signals (B=200Hz) have a world wide coverage. This will give you an idea on how good your antenna system is.
And you can compare your signal to an excellent receiving system at the Netherlands: http://websdr.ewi.utwente.nl:8901/
At my place (southern part of Germany) I can receive the signals with a SNR (SDRuno indication) of well above 20dB. And it is only SNR which is the determining factor, NOT signal power!
My antenna system: a plain VHF discone. No LNA, no filters etc.

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Paul
Posts: 90
Joined: Fri Feb 17, 2017 9:52 am

Re: RSP2 & NDB RECEPTION

Postby Paul » Wed Aug 09, 2017 11:08 am

Thanks for your interest JMG
Something more to look at - but to be honest, I'm still "building" my current setup and although for general purposes, it's working pretty well, there is certainly plenty of scope for improvement.
Wellbrooks are certainly interesting and I may have a go at building one, time and ability permitting (or get some one I know who could).
Just as an aside, my last employment (before retiring) was for three years in Nuernberg.
I had lived in Germany before, but absolutely loved that area.

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