NDB reception

[Paul]

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.

[Mike2459]

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.

[g1hbe]

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.

[Paul]

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.

[g1hbe]

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).

[Paul]

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

[Paul]

Hi Andy
Thanks for all the useful advice re NDB reception.
Did a bit of antenna "fettleing," replacing the RAS0Ms mini-whip on port A with another version from the Ukraine (I doubt my ability to make my own) and using it on Port A, I am now able to get pretty good NDB reception (mainly using your preferred AM mode for most) in the 320 - 430 KHZ area.
Generally receiving beacons out to about 200NM from my QTH, with the single exception of Horta in the Azores.
Apart from finding this little antenna a great deal more sensitive in this area, your advice was invaluable.
I recognise that using the HI-Z port would be a better option, but I've dedicated that to the simple end-fed long-wire, which works well, so there I'll leave it (I think).
It was an interesting exercise and ultimately satisfying, but I'll try not to get "hooked."

[GM4FDM]

Perhaps there are less NDBs about than there used to be - I suppose a great deal depends on your location??

[13dka]

Glad you get reception "down there" now. However, while a miniwhip-style antenna gives surprisingly good results even "down there", a simple wire loop will beat it on many occasions.

Here's a comparison of VLF and NDB reception with a dipole vs. a loop of the same wire length. Actually it's the very same antenna, which is a rather odd contraption I made (by accident) specifically for the RSP, meant to give both good SNR, good wideband capabilities and some built-in attenuation to keep the RSP overloading in check. It's basically a 2x10m dipole with a deliberately not matching balun (the infamous NooElec 9:1 balun) used on both sides of the coax. Putting that thing at the very same spot (in some trees in my case) into a delta (or whatever kind of) loop configuration by simply connecting the wire ends is fundamentally changing its properties of course, to the benefit of low frequency reception.

Here are some animated GIFs to demonstrate:

VLF_crappole_vs_craploop.gif (163.95 KiB) Viewed 81038 times

This shows the impact of the configuration on VLF reception. As you can see, the difference is quite noticeable, spurious signals tend to disappear and actual on-frequency signals get a much better SNR. You can clearly see (and hear of course) the 60 and 77kHz time signals, that were much in the noise before in the dipole configuration.

Here's the NDB band:

NDB_crappole_vs_craploop.gif (212.67 KiB) Viewed 81038 times

The difference is obviously even more pronounced here. The NDB band more or less doesn't exist in the dipole configuration, in the loop configuration I get some additional muck but also a lot of NDBs. Here's what the band typically looks like then:

NDB_Love2.jpg (224.57 KiB) Viewed 81038 times

As you can see, there's quite a lot of them to see clearly, and a lot more of them to pick up in much noise using narrow CW filters and a lot of patience (since they're often fading in and out slowly, interfering with others on a nearby frequency and so on). To my own surprise, I found hunting NDBs a fun challenge, at least for a few days and I'll most likely do it again!

Here's a typical log of 3 days of NDB hunting, they're from all over Europe:

Code: Select all

517	JBR	Jaszbereny (Budapest)	HU		1069km
514	GO	Amari Airbase		EST		1093km
492	TBV	Trebova			CZ		 723km
490	WAK	Vakarel			BG		1684km
488	ILM	Illesheim  		D		 528km
485	IA	Indija      		SRB (Belgrad)	1330km
484	HOF	Hof			D		 473km
478	MF	Larionovo		RUS		1854km*
468	FTZ	Fritzlar     		D		 335km
458	LP	?
452	ANS	Ansbach			D		 550km
448	HLV	Holesov			CZ		 803km
448	LQ	Landsberg		D		 698km
438	KO	Kozala			CRO		1057km
434	MV	Melun-Villar.		F		 755km
433	VNS	Castor Platform		ESP		1650km
433	CRE	Cres			CRO		1095km
432	PK	Pardubice		CZ		 656km
431	KBA	Karlsruhe	              	D		 571km
430	SN	St. Yan			F		 924km
429	LOS	Losinj			CRO		1123km
428	MUS	Nice Cote d'Azur     	F		1165km
428	CTX	Chateauroux		F		 958km
427	RY	Royan			F		1179km
426.5	MIQ	Mike Ingolstadt		D		 623km
426	GBG	Gleichenberg		A		 948km
424	PIS	Pisarovina		CRO		1074km
424	PHG	Phalsbourg		F		 606km
423	ZO	Nis			SRB		1532km
423	FE	Odense			DK
421	BL	Borlange	                            S		 809km
421	MF	Halmstad	              	S		 379km
419	EMT	Epinal			F		 683km
419	RD	Vasteras	              	S		 767km
418	MK	Mark Calais		F		 590km
417	AX	Auxerre Branches    	F		 792km
417	AH 	Angelholm		S		 346km
416	BCS	Bacchus			S		1052km
415	OL	Linkoping Saab		S		 633km
415	RTB	Rothenbach		D		 542km
414	HD	Hestad			NOR		 818km
414	BRI	Bristol			GB		 824km
414	BOA	Bologna			I		1069km
412	SE	Strasbourg		F		 622km
410	ETN	Etain			F		 590km
409	SG	Satenas			S		 534km
406.5	BOT	Bottrop			D
404	Y	Kemi			FIN		1378km
404	LW	Luxembourg		LX
404	MRV	Merville    		F		 572km
403	OJ	Jonkoping		S		 523km
402	LX	Ekilstuna   		S		 745km
401	COD	Codogno			I		 999km
400.5	EJ	Esbjerg			DK
400	EN	Orebro			S		 690km
400	ONO	Oostende	              	BEL		 514km
396	YG	Enge			NOR		1386km
395	GE	Billund			DK
394	NB	Bromma (Stockholm)	S		 801km
394	NV	Nevers			F		 890km
392.5	TOP	Torino			I
392	RAN	Lappeenranta		FIN
388	BR	Lyon			F		 973km
388	COR	Corner (Stockholm)	S
388	KRU	Kruunu			FIN		1412km
387	SLT	Sylt (aua)		D
387	SLV	Spa			BEL		 453km
387	ING	Saint-Inglevert		BEL		 601km
386	O	Kardla			EST		1005km
386	LNE	Linate			I		 966km
384	TY	Torsby			S		 712km
383.5	GUL	Gulpen			NL
383	ERK	Erken			S		 865km
382	SBG	Salzburg   		A		 762km
381	RG	Rygge			NOR		 596km
380	FLR	Trondheim		NOR		1038km	
380	HO	Colmar/Houssen		F		 681km
379	VEN	Venezia			I		 999km
379	EB	Saint Etienne/Boutheon	F		1018km
378	RSY	Rennesøy (Stavanger)	NOR		 583km
378	OS	Sundsvall	              	S		1041km
377	KN	Norkoping		S		 670km
377	SM	Siljan/Mora		S		 576km
377	ORI	Orio Al Serio		I		 942km
376	HAN	Hahn			D		 478km
376	HP	Esbjerg			DK
375	RB	Orebro			S		 690km
375	GLA	Gland			CH		 876km
375	CV	Calvi/Corsica		F		1286km
374.5	ANC	Ancona			I		1218km
374	BGC	Bergerac   		F		1194km
373	NW	Maastricht		NL		 423km
371	HAA	Hamar			NOR		 753km
371	ODR	Odderoy			NOR		 448km
371	LEV	Levaldigi  		I		1070km
370.5	LB	Angelholm		S		 346km
370	PSA	Spessart   		D
370	BSV	Besancon		              F		 792km
369	NL	Landvetter		S		 446km
369	ELU	Luxembourg		LX		 515km
368	RK	Roskilde	              	DK
367	BYC	Bueckeburg		D
367	VAT	Vatry			F		 671km
366	UTH	Uthaug			NOR		1067km
366	KM	Kalmar			S		 551km
365	VS	Vesilahti	               	FIN		1181km
365	LJ	Koeln/Bonn		D
364	NW	Stockholm		S		 805km
363	PI	Poitiers    		F		1032km
363	OEM	Kristianstad		S		 398km
362	BVK	Baatvik			NOR		 984km
362	NN	Ekilstuna		              S		 745km
361	NB	Bordeaux  		F		1235km
361	MAK	Mackel			BEL		 502km
360	ASK	Bergen Askoy		NOR		 739km
360	SR	Ensheim			D		 483km
360	ULV	Ulvingen		              NOR		1290km
359	LOR	Lorient			F		1109km
358	GRK	Grakallen		              NOR		1036km
357.5	FAL	Falconara		I		1214km
357	SME	Olbia Costa Sardinia	I		1470km
357	KD	Kolding			DK
357	VZ	Eelde			NL
356	SGO	Sagunto			ESP		1747km*
355	ONW	Antwerpen		NL		 441km
354	PAD	Paderborn		D
352.5	DD	Oostende	              	BEL		 540km
352	PLA	Pula			CRO		1090km
352	LAA	Laarbruch		D		 335km
352	PSJ	Seinajoki		              FIN		1255km
351	OV	Visby			S		 704km
351	ROT	Rotterdam		NL		 382km
349.5	SZA	Solenzara (COR)		I		1368km
349	JX	Vaxjo			S		 483km
349	TAR	Tarva/Orland		NOR		1075km
348	WA	Arlanda			S		 823km
347	CVT	Chalons			F		 654km
346	AU	Stauning	                  	DK
346	WLU	Luxemburg		LX		 515km
346	LHO	Le Havre		              F		 791km
345.5	CF	Caslav			CZ		 648km
345	BN	Birkeland	              	NOR		 468km
343	KUS	Kaunas			LIT		 973km
342	SL	Landvetter		S
342	LL	Leirin			NOR		 766km
341	NKS	Karlstad    		S		 648km
341	IS	Ajaccio	(Corsica)	              F		1358km
339.5	SD	?
338	OA	Jonkoping		S		 523km
337	MY	Myggenes		FO		1261km
337	LHR	Lahr			D		 648km
336	LT	Halmstad	              	S		 379km
335	BER	Bern			CH		 805km
334	POY	Paris Orly		F		 750km
333	LE	Vasteras   		S		 767km
332	NV	Nieuwkoop		NL
332	VOG	Voghera			I		1016km
331	TUR	Tours			F		 943km
330	SO	Eelde		             	NL
330	SKS	Karlstad	              	S		 648km
330	OB	Bratislava		SLO		 879km
329	NMS	Namsos			NOR		1158km
329	VX	Vaxjo			S		 483km
329	SB	Sonderborg		DK
327	LNZ	Linz			A		 749km
326	LM	Le Mans			F		 909km
325	PG	Trollhättan		S		 508km
324	ON	Norkoping		S		 670km
324	DP	Diepholz	              	D
323	ONC	Charleroi  		BEL		 511km
322	OU	Stockholm		S		 805km
321	VO	Val D'Or		              F		 653km
320	VE	Chabeuil	              	F		1063km
319	VAR	Varhaug			NOR		 536km
318	LP	Ronneby			S		 469km
318	RW	Tegel West		D
318	CP	Parduc			HU		 974km
317	OZ	Kardla			EST		1005km
316	TNJ	Tounj			CRO		1091km
316	IN	Sonderborg		DK
314	HOL	Villacoublay		F		 752km
314	OZ	Brussels Natl		BEL		 475km
311	LMA	Lima (DUS)		D
309	DO	Dole Tavaux		F		 824km
307	DIK	Diekirch		              LX		 505km
306.5	AV	Avord			F		 902km
300.5	CMP	Compagnano		I		1269km
300	SC	Linkoping		S		 633km
299.5	KN	Svolvaer	              	NOR		1596km
293	OB	Brussels    		BEL		 475km
290	ONL	Bieset			BEL		 450km
285	LCF	?			S
284	FSB	Fassberg	              	D

(Grr, seems there's no way to keep a tab-formatted list aligned.)

As you can see, the most distant ones are 1700-1800km away and I've seen logs with even bigger distances, and I can feel a bit of that urge to improve my rig to get even more distant NDBs myself. It think that is the magic of NDB hunting, you have very weak signals from fixed and known locations on published frequencies that sit there and transmit all night, giving you the ideal counterpart for improving your stuff to receive them and improving your skills to search and identify them, which can be quite some detective work. Utterly nerdy fun.

Perhaps there are less NDBs about than there used to be - I suppose a great deal depends on your location??

Well yes, some NDBs have been turned off in the past 10 years but surprisingly it seems VORs are more affected by cost reduction attempts than NDBs, which may have to do with the higher maintenance efforts and the fact that many NDBs are still important waypoints on ILS approaches (such as marking the Initial Approach Fix etc.). Most NDBs I still get are located on or near an airport, rather than "enroute"-style beacons. This does matter in that the co-located beacons usually have much less power output.

But location is important too of course, as well as antenna orientation (which is probably less of an issue with a miniwhip tho).

[CaptainNemo]

@13dka
very impressive
can you post some details about your loop? horizontal I suppose...
(I have already tried a loop but with no success)
thanks in advance
gio