NDB reception

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Paul
Posts: 78
Joined: Fri Feb 17, 2017 9:52 am

NDB reception

Postby Paul » Mon Jul 24, 2017 8:01 pm

I am about to display my ignorance yet again - Whilst I receive excellent quality cw/morse code signals all over the HF bands and have two antennae connected to Port A (Active mini-whip) and long-wire to the Hi-Z port pf an RSP-2, that perform well in the 190khz and upwards range, I have been unable to find any (even after having resorted to listed beacon frequencies).
Although it is not my primary area of interest, I would be grateful to anyone who could offer a suggestion as to why this may be the case.

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Mike2459
Posts: 13
Joined: Mon Jul 24, 2017 8:24 pm

Re: NDB reception

Postby Mike2459 » Mon Jul 24, 2017 8:36 pm

It's been a long time since I've listened to NDBs, but perhaps I can help. If there are any within a 50km radius of your location they should be readable 24 hours a day. Otherwise listen after dark. Using sideband or cw mode will help pick the carrier out of the noise, as it can detect signals that are inaudible in AM mode.
Last edited by Mike2459 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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g1hbe
Posts: 216
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: NDB reception

Postby g1hbe » Mon Jul 24, 2017 11:15 pm

Hi Paul. I occasionally listen around the beacon band and there are certainly beacons to be heard. There may be a couple of reasons why you aren't hearing much: First of all, neither of the SMA ports works well at LF (especially port B, which has a very poor LF response due to the bias-T circuitry), and this is covered in the user guide. The Hi-z port works very well from 10 KHz to 30 MHz and I see you are also using this port.
I wonder if you have a high noise level? My noise level has recently taken a turn for the worse and even my Wellbrook loop sometimes struggles to hear the beacons because of it. Noise from TV's, computers, phone chargers and anything that uses a SMPS is always worse at the LF end of the spectrum.
How is your wire antenna connected to the Hi-z port? Does the wire come straight into the shack or do you have some kind of coax feeder? If it comes straight in, that may be the problem, as the wire will pick up all the rubbish generated by the stuff in your home. It's also worth checking that you have wired the Hi-z connector as shown in the diagram. Sorry, I can't recall which user guide/cookbook the diagram is in!
Finally, in my experience mini-whips are just as bad as wires when it comes to picking up local noise, which is why I chose the Wellbrook loop. Nine times out of ten, it makes a signal audible when a wire (or my homebrew mini whip) just sees noise.

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Andy

Paul
Posts: 78
Joined: Fri Feb 17, 2017 9:52 am

Re: NDB reception

Postby Paul » Tue Jul 25, 2017 7:07 am

Hi Mike/Andy
Thanks for your responses - I am in a rural location and apart from some "frying" that I believe emanates from overhead three-phase power lines, probably about 50M from my qth, things aren't that bad (I think) and unless ndb's are particularly weak signals, I would have expected to be able to find at least one.
Perhaps my setup isn't as good as I think or would wish it to be, but in general everything seems to work pretty well.
Just for the record, the mini-whip on port A can equal or often exceed the 20M longwire on occasion as conditions vary.
Port B is a h/v/uhf discone, primarily used for v/uhf, but does perform fairly reasonably on HF, with the anticipated roll-off around 3-4MHz.
The longwire is orientated NNW/SSE (my best option) and attached according to the detailed instructions of the supplier and SDRPlay directly to the Hi-z terminal, being brought in via a >5M length of coax.
I did experiment with a 9:1 balun but wasn't sold on it.

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g1hbe
Posts: 216
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: NDB reception

Postby g1hbe » Tue Jul 25, 2017 8:33 am

Well it's a bit of a mystery! Do you get good sigs from the LW broadcasters? I'm clutching at straws now, but despite your rural location, it is worth looking at what SDRUNo reports as your background noise level. When my local noises are not on in the daytime, I get around -110 to -120 dBM at LF on the Wellbrook, but at least 20dB worse than this on my random wire and on the active mini-whip. This almost completely buries the beacons.
Just one final question, and I hope you won't feel insulted by it. Are all other signals on their expected frequencies? I ask this because a new user on one of the forums was bemoaning 'no signals and images all over the place', and to cut a long story short he had inadvertantly reversed the I and Q channels, putting everything out, plonking stations where they shouldn't be and silence where they should!
Sorry to have to ask, but sometimes it's easy to overlook these things.
The only other thing that springs to mind is de-sensitisation from big sigs in the MW band. Do you have any huge MW sigs there? The LF filter on the RSP2 reaches all the way up to 12 MHz, so everything gets in! It's also worth looking at the LNA gain level and reducing it (or increasing the 'gain reduction' setting).

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Andy

Paul
Posts: 78
Joined: Fri Feb 17, 2017 9:52 am

Re: NDB reception

Postby Paul » Tue Jul 25, 2017 3:27 pm

Thanks for the last Andy
I will persevere - all taken aboard - and no you would have to work harder than that to make me feel insulted...
I'm always grateful for any constructive comment.Best Wishes
Paul

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